Oud 07-02-2002, 16:15
legatus
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INTELLIGENT DESIGN: http://www.arn.org/id_faq.htm

Design theory—also called design or the design argument—is the view that nature shows tangible signs of having been designed by a preexisting intelligence. It has been around, in one form or another, since the time of ancient Greece.

The most famous version of the design argument can be found in the work of theologian William Paley, who in 1802 proposed his "watchmaker" thesis. His reasoning went like this:

In crossing a heath, suppose I pitched my foot against a stone, and were asked how the stone came to be there; I might possibly answer, that, for anything I knew to the contrary, it had lain there for ever. ... But suppose I had found a watch upon the ground, and it should be inquired how the watch happened to be in that place; I should hardly think the answer which I had before given [would be sufficient].

To the contrary, the fine coordination of all its parts would force us to conclude that

… the watch must have had a maker: that there must have existed, at some time, and at some place or other, an artificer or artificers, who formed it for the purpose which we find it actually to answer; who comprehended its construction, and designed its use.

Paley argued that we can draw the same conclusion about many natural objects, such as the eye. Just as a watch’s parts are all perfectly adapted for the purpose of telling time, the parts of an eye are all perfectly adapted for the purpose of seeing. In each case, Paley argued, we discern the marks of an intelligent designer.
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Oud 07-02-2002, 16:20
legatus
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Biological Evidences:

Darwin himself realized that there were certain types of biological structures which Darwinian evolution simply couldn't create. Darwinian evolution works by a process called the mutation-selection mechanism. Purely random mutations in the DNA create new types of organisms, and those organisms which are better at surviving and reproducing tend to leave more offspring. Over time, populations of organisms change as those which are best suited to the environment get "selected" (i.e. they survive and reproduce better). The catch to all of this is that changes must occur at a very slow pace, one little mutation at a time. Also, biological systems produced by evolution must be functional (i.e. confer some benefit to the organism) at every little step along their evolutionary path. For this reason, Darwin said:

"If it could be demonstrated that any complex organ existed which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down."

(Charles Darwin, Origin of Species)
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Oud 07-02-2002, 16:21
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Molecular biologist Michael Behe recently noted in his book, "Darwin's Black Box", that there are a host of biochemical systems which function much like machines. These machines work only if all the necessary parts are present for if one part is removed, the entire machine breaks down. These systems defy an evolutionary origin, because they cannot be built up in a step-by-step manner. Examples Behe gives include the bacterial flagellum, the blood clotting mechanism, and the biochemical processes behind vision. Reverse-engineering of these and other biological structures shows that evolutionary processes weren't at work in creating them.

William Dembski, in "The Design Inference" and "No Free Lunch" shows that Darwinian processes cannot explain much of biological complexity. Biological organisms--both at the macro and micro level--exhibit this sort of "irreducible complexity" and "specified, complex information. These properties of biological systems cannot be explained by evolution.

http://www-acs.ucsd.edu/~idea/evolutionfaq.htm
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Oud 07-02-2002, 16:24
legatus
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Zoals ik het al jaren niet kan slikken. De mens een produkt van pure evolutie?
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Oud 07-02-2002, 16:46
Joël
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Citaat:
legatus schreef:
De mens een produkt van pure evolutie?
Ik dacht dus van niet... Dat ene boek van die M. Behe, "Darwin's Black Box", heb ik hier ook liggen, en stukken van gelezen. Maar ja, ik ben ook maar een onwetend mensje zonder verstand van bio, dus 't is natuurlijk gewoon een mening, hè?
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Oud 07-02-2002, 16:47
Demon of Fire
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Bewijs voor de evolutietheorie.

[b]In the October 11th (1990) issue of Nature, Meyer et.al. present of paper aimed at establishing if the cichlid fish species of Lake Victoria (Africa) are monophyletic or polyphyletic. (If they all share a recent common ancestor in that lake or came from separate lineages that invaded the lake). In their paper they sequenced a 363 bp part of the cytochrome b gene and a 440 bp segment of mitochondrial DNA from what is called the control region. They sequenced these genes from several species of fish in the lake and a few species from relatively nearby lakes.

What they found was the sequences in the Lake Victoria species of fish were all very similar, but they were different from the sequences of fish in nearby lakes. All the sequences are listed in the paper.

They came to the conclusion that this indicated the cichlid species of Lake Victoria all derive from a recent common ancestor in the lake. They estimate the time of divergence at about 200,000 years ago based on a model that assumes mutations are relatively constant over time. (The lake, incidentally, had been independently dated to be 250,000 - 275,000 years old)

The News and Views section of that issue has an overview of the paper written by John Avise. Also, the cover photo of this issue consists of a picture of several of these fish.

Reference

Meyer, et. al., 1990, Monophyletic origin of Lake Victoria cichlid fishes suggested by mitochondrial DNA sequences, Nature 347: 550-553

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Introduction to speciation theory

This is part two in my series of postings on studies of an evolutionary nature. As I said in part one, I have two goals in for this series. One, to show that evolution is an accepted branch of mainstream science. And two, that contrary to the continual assertions of creationists, there is an overwhelming amount of data in favor of the theory of evolution. Again, note that no single post is intended as a stand alone proof. This post is divided into two section, an introduction (the part you are reading) to provide a bit of background, and the actual summary of the paper discussed.

Speciation occurs when two (or more possibly) subsets of a formerly interbreeding population become reproductively isolated. For many years, speciation theorists thought that virtually all speciation occured when the two subsets of the population where separated by geographical boundaries. (ie, the species became split by a river, mountain range or a small group migrated out of the main region inhabited by the species.) Reproductive isolation followed physical isolation as the two, now separate lineages, diverged. This could occur for many reasons, for example mating rituals grew different or chromosome numbers changed etc. etc. In any case the end result would be that the two lineages could no longer interbreed if they encountered each other. (Incidentally this type of speciation is called allopatric speciation).

A second type of speciation, sympatric speciation, occurs when two lineages of a formerly interbreeding population diverge to the point of reproductive isolation while still residing in the same locale. This was first demonstrated to occur by Guy Bush working on the Apple maggot fly Rhagoletis pomenella.

The paper I will outline here is one found in the August 9, 1990 issue of Nature. I will continue this discussion in my next post.

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Isolation mediated by microorganisms

In the paper outlined here (Breeuwer and Werren, 1990) the authors examine two species of wasps living sympatrically (in the same area).

Wasps (like ants, bees and termites) are haplodiploid organisms. In these organisms, females develop from fertilized eggs (so there is a male and a female contribution to the genome (i.e. sperm and egg)) while males develop from unfertilized eggs (so there is no male contribution to the male genome).

The authors of the paper experimented with two species of wasps, N. vitripennis and N. giraluti. They noticed that when they crossed individuals from different species, only males were produced. In other words, fertilization was not occuring. They found out that this was the result of microorganisms in the cytoplasm of the gametes destroying the males chromosomes from his sperm.

Microorganisms had been seen in the cytoplasm of the eggs of these species, but this alone did not prove that they were the cause of the reproductive isolation. So what they did was feed some wasps food that contained tetracycline, which kills microorganisms, and cross the wasps again. What they found was, in crosses in which all the microorganisms had been killed, the two species produced both male and female offspring. In crosses where the parents gametes still harbored the microorganisms, only males were produced in interspecific crosses. (Note that intraspecific crosses (matings in the same species) always produced male and female offspring)) Therefore they concluded that the microorganisms made it unable for the sperm from a different species of wasp to fertilize the females egg. This worked bidirectionally (N. vitripennis females to N. giraluti males and N. giraluti females to N. vitripennis males). The microorganisms did not, however, inhibit males and females of the same species from producing offspring of both sexes.

The authors then went on to speculate that microorganism induced reproductive isolation may be a quick way for sympatric speciation to occur. The paper also list some other cases of similar events occuring in other organisms.

Reference

Breeuwer and Werren, 1990, Microorganisms associated with chromosome destruction and reproductive isolation between two insect species, Nature 346: 558 - 560

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The basics of sexual selection

This is part three in my series of postings. In this post I describe a paper presented in the July 12, 1990 issue of Nature dealing with sexual selection in katydids (an insect). I am going to break this up into two articles, one to outline the underlying theory and another to describe the experiment.

The paper I will outline deals with sexual selection. It is well accepted that the most intense competition an organism faces is with members of its own species. Many species tend to have limited diets and habitat requirements, and an organism must compete with members of his own species to secure these necessities. Of primary importance, however, is procuring a mate. If an organism fails to do that it's genes are eliminated from the gene pool. (Note that in nature there is never enough food, habitat and/or mates to go around. There are always more offspring produced in a population than will be able to reproduce.)

In many (if not most) animal systems, females choose the males they wish to mate with. Conversely, males compete for access to females. For example many male birds defend a territory in order to attract females. In many mammals (ie sheep) the males (rams) engage in contests to determine which male gets to mate. Obviously the female will choose the male who wins because her sons will then have the genes for winning these contests and females will choose them. [as a sidenote this kind of "logic" on the part of females can lead to what is called "runaway sexual selection". This occurs when the traits favored by sexual selection become linked with the genes for preference of that trait. This can often push the system in such a way that traits with a lower survival value are favored because their sexual attractiveness outweighs their negative survival value. The tail of the male peacock is an oft-cited example of this - but that's another story].

But why should females be the one's who choose? Why don't females compete for access to males? To answer this question, Darwin speculated that the sex that contributed more energy to the production of the offspring would be the sex that would be able to exercise preference. His theory of sexual selection was later expanded upon by Williams and Trivers.

In most animal systems it is clearly the female who devotes the most energy to the production of offspring. The female gamete (egg) is many times larger than the male gamete (sperm). In addition, in mammals, females must carry the offspring until birth. And furthermore females of many species provide the lions share of parental investment after the offspring has been born.

In the paper I will present in the next article the authors experimentally test the hypothesis that the sex devoting the most energy to the production of offspring will be the sex that exerts a choice amongst mates.

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Experimental reversal of parental investment

In their paper, the authors (Gwynne and Simmons, 1990) experiment on a katydid of, as yet, unnamed species and genus. This species of katydid was observed to be highly variable in male contribution to parental investment. In these insects, the males transfers a spermatophore to the female after copulation. The spermatophore contains the ampulla, which contains the sperm, and the spermatophylax, which the female eats. The spermatophylax has been demonstrated to increase both the number and fitness of offspring sired by the male (it is a source of nutrition to the female).

In their experiment the authors set up two cages. In cage one (the control) the katydids were allowed to feed on the pollen of their host plants. In cage two the katydids were allowed to feed on the pollen, but were also provided a nutritional supplement (the experimental cage). Therefore, in the control cage (with limited food) the value of the males spermatophore is much greater to the female. Females were introduced to both cages and their behavior was observed.

In the control cage (with limited food) the males exerted a mating preference and females competed for mating opportunities with males. This is because, with a scarcity of food, the male spermatophore became a valuable asset.

In the experimental cage, the females exerted the mating preference because with an abundance of food, the male spermatophore was not such a valuable asset. In this way the authors showed that (in katydids at least) the parental investment is the determining factor in courtship roles (i.e. which sex exerts the mating preference)

Reference

Gwynne and Simmons, 1990, Experimental reversal of courtship roles in an insect, Nature 346: 172 - 174

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Whale with legs

This is my fourth posting in my "evidence for evolution" series. This will be a short one. It's a short, gee-whiz paper from Science. In my next post (tomorrow, maybe) I'll explain a paper in Nature in which the authors sequenced DNA from a 17-20 MY old magnolia leaf. I'll tell what they found (it's cool) and how they did it (also cool).

In the July 13, 1990 issue of science, Gingerich et. al. report on an interesting fossil found in Egypt. It is a whale with feet. The skeleton is of the species Basilosaurus isis. This whale lived in the Eocene period (in Egypt (then under water obviously)).

Current cetacea (whales), as you are no doubt aware, do not have external hind limbs. But whales, which are mammals, evolved from terrestrial mammals. This fossil, therefore, is a link between the two. The skeleton they show is long (16 m) and serpentine. The authors believe this whale hunted in shallow mangrove or seagrass habitat. It's hind limb has a short femur and a slightly shorter fibula and tibia. It has no thumb and a greatly reduced second digit. The other three fingers are quite long (relatively). In short, another variation of the basic mammalian leg.

The authors speculate that the limbs were tucked in close to the body while the whale was swimming (and the topography of the bones suggest that they are correct). Furthermore, they go on to speculate that the limbs served as a copulatory guide for the whale.

The one thing I didn't like about the paper was a lack of actual photographs of the specimen. They gave graphs and schematic diagrams of all the salient features, but no photos. I would think that in a paper of this nature, a picture would have been worth a thousand words. Maybe they are working on the reconstruction and want to complete it before display.

Reference

Gingerich, et. el., 1990, Hind Limbs of Eocene Basilosaurus: Evidence of Feet in Whales, Science 249: 154-156

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Introduction to polymerase chain reaction (PCR)

This is my fifth posting in my "evidence for evolution" series. In this post I will explain a paper in the April 12, 1990 issue of Nature in which the authors sequence a 17-20 million (yes, thats million) year old DNA sequence from the chloroplast of a fossilized Magnolia plant. I will use this post to make two points (besides the usual). One, to explain the significance of their actual results. And two, to introduce you to a new molecular biological technique that has opened up a vast horizon of possible molecular evolutionary studies. The technique is called polymerase chain reaction (or PCR for short). This first article describes the technique. The second article will describe it's application. This article assumes some knowledge of basic molecular biology. I give a reference for a more detailed discussion near the end.

PCR is a technique that allows a researcher to pick a region of DNA from a very small sample and amplify it to some usable quantity. It works by iterating cycles in which only the region of interest is amplified.

At the beginning of a cycle the DNA is double stranded (I'll call the strands the + and - strands). The DNA is then heated and the strands come apart. Then the DNA is cooled. As it cools, primers bind the DNA. These primers are short oligonucleotides chosen by the experimenter and added to the DNA mixture at the beginning. They flank the region to be amplified. One binds to the + strand and the other binds to the - strand. Their 3' ends both face the region to be amplified (remember DNA is synthesized in the 5' to 3' direction) so that polymerization can only occur in that region. A DNA polymerase then begins adding nucleotides to the 3' end of both primers, synthesizing a new - and + strand of the region of interest. Next, the reaction mix, (which includes the DNA sample, the primers, single nucleotides and the polymerase) is again heated and then cooled. This is repeated many times.

The result is the following. In the first cycle the + and - strand serve as a template and a new - and + (respectively) copy of the area of interest is made. When the cycle is repeated the primers now have more sites to bind to, the original sample DNA sites and the newly synthesized DNA sites. As the cycles continue, the number of possible primer binding sites doubles each time. Therefore in a short amount of time a negligible amount of DNA can be amplified to a workable quantity. This is because the amount of templates is geometrically increasing each cycle.

This is extremely hard to portray in words. A diagram of this technique makes things crystal clear. Many biologists I know, including myself, when first exposed to the idea of PCR said, "Why the hell didn't I think of that?". It is a very powerful and elegant technique. For a good, accessable overview (with the pictures to ram the idea home) see the April, 1990 issue of Scientific American (p 56, The Unusual Origin of the Polymerase Chain Reaction).

One further thing is worth mentioning. When you heat the DNA, everything else in the reaction mix is going to be heated along with it. At the temperature DNA denatures (strands separate) proteins from most organisms (like DNA polymerases) also come apart. This presents a problem. Either the researcher would have to add new polymerase each cycle, or a heat stable polymerase would have to be found. In fact, a heat stable polymerase has been found and is used for PCR. The polymerase is called Taq polymerase. It is call Taq because it comes from the organism Thermus aquaticus, a bacteria that lives in thermal vents in the ocean. Since the organism lives in water averaging close to boiling, it's DNA polymerase is stable at these high temps. And, therefore the Taq polymerase can be added to the reaction mix at the beginning and will remain active throughout all the cycles.

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DNA sequenced from 17-20 MY old magnolia

In the paper I explain here, the authors (Golenberg et. al., 1990) sequenced an 820 bp region (the rbcL gene) from the chloroplast DNA of a compression fossil of a magnolia.

[A brief explanation of chloroplasts (and their DNA): Chloroplasts are organelles found in the cells of plants. They are the site of photosynthesis. These organelles are autonomously replicating (i.e. there replication is not tied to the cell cycle.) They contain their own genome, a single, circular "chromosome". DNA sequences of their "genomes" and their autonomous nature led Lynn Margulis to speculate that chloroplasts were once free living organisms that later became endosymbionts in other cells. She also thinks this explains the presence of mitochondrian in cells (as well as basal bodies). This is now generally accepted. But, that's another story]

The fossil leaf they extracted the DNA was from a compression fossil formed when the leaf sank to the bottom of a lake. The conditions were very anoxic (lacking in oxygen) and as a result the fossil was in very good condition. In the News and Views section of the same journal they show a photo of the fossil; the leaf was still green! And, as you will see, it still contained DNA. They authors mention that many well preserved compression fossils were recovered. These fossils were from organisms living in the Miocene, 17 - 20 million years ago!

Anyway, the authors extracted what DNA they could from the fossil and amplified the rbcL gene via PCR. The primers they used were 30 bp oligonucleotides synthesized to match the sequence of Zea Mays (corn). Since rbcL codes for a necessary protein, ribulose-1,5-bisphosphate carboxylase, they expected the sequence to be conserved enough for the primers to bind. It was. They also ran some tests to insure the sequence they got was actually from the fossil and not an outside contaminant. It was.

The sequence of the fossil and two extant species of magnolia are given along with one other plant species. The fossil magnolia, given the species name Magnolia latahensis, yielded a sequence similar, but distinct from the extant species of magnolia. The magnolia sequences (fossil and extant) formed a cluster distinct from sequences of closely related species (tulips and petunias for example).

The authors conclude that the sequence they got was from the fossil and that the fossil was from a now extinct species of Magnolia.

The power of this technique (PCR) suggests many applications for evolutionary biologists. Any organism in which the tissue is intact can potentially yield enough DNA to sequence. (This includes insects in amber, wooly mammoths and museum specimens) This knowledge can be used to resolve phylogenies of extinct organisms. Also, if enough samples are available, one could estimate the genetic diversity of past populations of organisms and how it changed through time. There has already been a paper of this nature in Journal of Molecular Evolution. In that paper the researcher traced the genetic diversity of Kangaroo Rats of California. Someone in my lab is doing the same thing on an endangered species of beetle here in Massachusetts. She is getting the DNA from pinned museum specimens that go back over one hundred years.

Reference

Golenberg, et.al., 1990, Chloroplast DNA sequence from a Miocene Magnolia species, Nature 344: 656 - 658

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Sexual selection 2

In this post I present two models of sexual selection and a paper that tests one of the predictions of both models. The first article in the post will be an exposition of the theory and the second article will be a discussion of the paper.

Darwin, and others, noticed that in many species males developed prominent secondary sexual characteristics. A few oft cited examples are the peacocks tail, coloring and patterns in male birds in general, voice calls in frogs and flashes in fireflies. Many/most of these traits are a liability from the standpoint of survival, mainly because an ostentatious display to attract females is also going to catch to the eyes/ears/nose/whatever of predators. How then could natural selection favor these traits? Well, as I pointed out in a previous post, the sexual attractiveness of these traits outweighs the liability incurred for survival. A male who lives a short time, but produces many offspring is much more successful than a long lived one that produces few. His genes will eventually dominate the gene pool of his species.

There are two competing theories as to why females are attracted to male displays. One model, the "good genes" model, states that the display indicates some component of male fitness. A "good genes" advocate would say that bright coloring in male birds indicates a lack of parasites. The females are cueing on some signal, in this example color, that is correlated with some other important trait (ex. parasite load).

The second model, proposed by Fisher, is called the "runaway sexual selection" model. In his model he proposes that females develop a preference for some male trait (without regards to fitness) and then mate with these males. The offspring of these matings will therefore have the genes for both the trait and the preference for the trait. Note, these genes would be expressed in the males and females respectively. As a result the process snowballs out of control until natural selection brings it into check. An example to clarify.

Suppose, due to some quirk of brain chemistry, female birds of one species prefer males with longer than average tail feathers. Males in the population with longer than average feather will therefore produce more offspring than the short feathered males. So in the next generation, the average tail feather length will increase. As the generations progress, tail feather length will increase becuase females prefer not a specific length tail, but tails a little longer than average. Eventually tail feather length will increase to the point were the liability to survival is matched by the sexual attractiveness of the trait and an equilibrium will be established. Note that in many exotic birds male plumage is often very showy and many species do in fact have males with greatly elongated feathers. In some cases these feathers are shed after the breeding season.

In both of these models, which are not mutually exclusive, it is predicted that female mating preference will be correlated with the male trait. In the first case because the trait is a signal for some other, underlying beneficial trait. In the second case because the the genes for the trait and preference for the trait are, or become linked.

In the paper I will present, the authors test this prediction. Their paper is not an attempt to discriminate between these two models. If the common prediction of both of these models turned out to be false, then both the models would have to be given the boot. That is the justification for the study.

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Trait correlates with preference

In the paper I discuss here, the authors (Houde and Endler,1990) conduct experiments on the guppy Poecilia reticulata. They collected these fish from 7 different streams that harbor these species. Each stream differed in the color pattern of male fish residing there. Male guppies had orange coloring covering from between 5% to 17% of their body, depending on which stream they came from.

They experimented by placing 6 males and 6 females in a tank and measuring the sexual attractiveness of the males. This was calculated as percentage of male displays that elicited a response from the female. In each separate experiment all the males were from one locale and all the females were from the same or another locale. They tested most, but not all, of the possible combinations of male/females.

They found that, female guppies from streams where males had large amounts of orange coloring strongly prefered male guppies with large amounts of orange to males with less orange. In populations where males had low amounts of orange coloring the females had no real preference with respect to coloring. The preference exhibited by females in the first sentence was, of course, statistically significant.

They interpreted this as, in the populations where coloring is prominent, evolution of female preference is correlated with the evolution of the male trait. In the populations where coloring is less prominent, there is no association between the male trait and the female preference.

The authors also mention a few factors that may confuse the issue. It had previously been shown that females in lightly predated waters favored brightly colored males more than females in heavily predated water.

In addition, a similar experiment by Kodrick and Brown had shown that females always prefered prominently colored males. They point out however, that these fish were from highly inbred lab stocks whereas Houde and Endler used fish recently sampled from nature (all the fish were less than three generations removed from the wild).

To conclude, the authors reach the conclusion that female preference and male trait are correlated in populations where the male trait is prominent. This was a prediction of both the "good genes" and the "runaway sexual selection" model.

Reference

Houde and Endler, 1990, Correlated Evolution of Female Mating Preferences and Male Color Pattern in the Guppy Poecilia reticulata, Science 248: 1405 - 1408

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Sperm competition in 13 lined ground squirrels

Here's number seven in my series. It's about sperm competition and male mate choice in 13 lined ground squirrels. As I have said before, each post is just the summary of some current paper published in a mainstream peer reviewed journal. This shows that evolutionary biology is a valid. productive branch of science and is recognized as such by the scientific community as a whole. No article is meant as a capsule proof of evolution.

In most species, females choose the males they wish to mate with. This is not the case in the thirteen lined ground squirrel, Spermophilus tridecemlineatus. In this system, oestrous females mate with any male that approaches them. On average a female will have two matings. The first male to mate will sire more of the offspring than the second (this is due to sperm competition). The ratio of first male offspring to second male offspring is modulated by two factors: delay between matings and duration of second mating. The longer the delay between the first and second mating, the less offspring the second male will sire. He can increase this number, however, by increasing copulatory time.

So, when a male arrives at a female who is already being courted he has two choices. (note, the first male on the scene is always the first to mate) He can wait until the first male leaves, or attempt to find a new female (hopefully an unmated one). As it turns out, females are scarce enough that it usually pays for the second male to wait. Siring fewer offspring is preferable to not finding a mate and siring none. However, males had been observed in the field rejecting certain females (ones who had mated awhile earlier) and searching for a new mate rather than going for the sure copulation.

The authors worked out a mathematical model (a fairly simple one) that showed, after a long enough time has passed since the first mating, the second male is going to sire a negligible amount of the female litter (due to sperm competition, remember the first male sires more and the proportion gets larger as time goes on). In this case the probability (although low) of producing offspring from an unmated female that he still has to go locate is greater than the probability of producing offspring from the female he has located. (Actually it's a bit more complicated than this, but this simplifies the picture without (IMHO) distorting it) The author calculated that the critical time to be 3.8 hours, after that a male should reject a previously mated female.

The authors then observed the squirrels mating and observed that second matings did, in fact, decrease in time. They also found that, on average, males would reject a previously mated female if she had mated 3.82 hours earlier.

The authors concluded that, since the behavior of squirrels closely matched their predictions. And, since their predictions were formulated based on sperm competition; sperm competition is most likely the factor determining male acceptance/rejection of mated females in 13 lined ground squirrels.

Reference

Schwagmeyer and Parker, 1990, Male mate choice as predicted by sperm competition in thirteen lined ground squirrels, Nature 348: 62 - 64

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How do squirrels "know" 3.8 is the magic number?

In regards to my previous squirrel post (actually two), the thought just crossed my mind that some people might get the wrong idea (or heaven forbid want to ridicule evolution by making a straw man of what I said) about how male ground squirrels "know" to reject previously mated females.

First off I would like to make it quite clear that the squirrels do not need to be trained in math to determine this. They don't avoid previously mated females after 3.8 hours because they understand the underlying mathematical model, but because natural selection favors males who "know" 3.8 is the magic number. Allow me to elaborate.

If a male happens upon a female who had mated, oh lets say 2.4 hours previously, decides to go looking for a new mate, (on average) he would sire less offspring than if he would have waited. Likewise, if a male waits 5 hours after the first mating for his chance, he will (on average) produce less offspring than had he wandered off to search for a new mate. However, males who, for whatever reason, go searching for mates after 3.8 hours will on average produce more offspring than males who wait any other amount of time. And as time goes on their offspring (who "know" to start searching after 3.8 hours) will come to make up a larger and larger percentage of the gene pool. Natural selection will favor males who search for a new mate when the female they find has mated 3.8 hours or more ago.

So males don't need to run around with calculators to figure out how long to wait, the answer has been passed on to them by their male ancestors who, by chance, hit upon the right length of time.

One last question could be asked. How do males know if and how long ago the female mated? I don't know the answer to this. Any thirteen lined squirrel experts out there? It could be any number of things. Even a rough estimate could be beneficial to the male.

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Swordfish and female preference

In one of my earlier posts in this series, I presented two (non mutually exclusive) models of sexual selection. Those were the "good genes" model and the "runaway sexual selection" model. Well, there is actually a third model out there also (which does not exclude the others). I'm not aware of any name for it, I'll just call it the "existing female preference" model. According to this model, females have a built in preference for a certain type of male, even if that type of male does not exist.

The paper I summarize here is in the Nov 9, 1990 issue of Science. In the article, the author claims that, in swordfish, the female preference for males with swords existed before males had swords.

Within the genus Xiphophorus there are swordless platyfish and swordtails. The swordless state is considered to be ancestral. Basolo (the author) experimented with females of the species X. maculatus. Males of this species are swordless. He placed a female in the center of an aquarium that was sectioned into three areas. On one side, he placed a normal male. On the other he placed a male with an artificial sword attached. She noted that the female prefered (stayed on that side of tank and offered mating displays) the male with the artificial sword. The experiment was redone and males switched sides (to control for side bias). The result was the same, the female prefered the male with the sword to the swordless male.

The author further experimented to determine if it was the sword itself the female was cueing on. To do this she repeated the above experiment except in this case both males had artificial swords. One sword was colored, the other was opaque (clear plastic). In this case the female prefered the male with the colored sword. The control (for side preference) was also run. In addition, the author removed the swords and switched them between males and ran the tests (and controls) again. The results were once again, the same. The female prefered the male with the visible sword.

So, the data she collected were. [small aside, yes the word "data" is plural. "Datum" is the singular. Computer types simply misused the term often enough that it has become accepted in computer literature]

Females (from this species that had never seen males with swords) prefered males with swords.
The females were not cueing on some side effect of the sword. (The clear vs. colored sword showed this. One possible side effect the female could have cued on was a unique swimming motion induced by the presence of the sword)
The female (in the colored vs. clear sword experiment) was not cueing on some other trait of the two males. (The switching swords experiment showed this. When the swords were switched, her preference switched.)
The author then concluded that the females in this genus have a pre-existing preference for males with swords. It is not surprising then that many species in the genus have swords, males have exploited this bias. What may be surprising to some is that some species don't have swords. This (IMHO) illustrates a pervasive misunderstanding that most people (and sadly many biologists) have about evolution. Evolution is not goal oriented. In this case there is no "selection pressure" for males to develop swords. They are not being pushed to develop swords. If, by chance, one males fins by chance happen to be longer than the other males in his population, he will enjoy greater reproductive success (because he is more "swordlike" than the others). This could continue until enough mutations have been selected for that males in this species have swords. But (and this is a very important but) there is no mechanism that is directing this to happen. In other words, there is no pressure on the males to develop swords. It's a fairly subtle point that is hard for many in our culture to accept. We live in a culture that likes to view things in terms of progress or heading towards a goal. Evolution is neither progress nor goal oriented.
Reference

Basolo, 1990, Female preference predates the evolution of the sword in swordtail fish, Science 250: 808 - 810

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Genetic drift and Mullers ratchet

Here's a switch, I'll try posting something productive instead of flaming people. I'll discuss here a paper in a recent issue of Nature. The author, Lin Chao, examined the RNA virus phi 6 to see if Muller ratchet was operating. I'll post this in two parts. In part one I'll explain what Mullers ratchet and genetic drift is. In part two I'll summarize the paper and explain it's significance.

H.J. Muller proposed, in 1964, one reason why sex may be beneficial to organisms. In a strictly asexual lineage, recombination is not possible (in sexual lineages it, of course, is). Thus, any mutation that occurs in an asexual lineage can only be corrected in one of two manners. The back mutation can occur or a compensating mutation can occur. Since mutations occur at random, the probability that the next mutation occuring in the lineage is the back mutation is low. Thus, each new mutation the lineage absorbs is likely to be a unique mutation. And, since mutations are most often deleterious; an asexual lineage is expected to decrease continually in fitness. Compensating mutations are also highly unlikely. This continual decrease in fitness, driven by mutations, is called Mullers ratchet. The term comes from the idea that each mutation moves the "ratchet" one notch forward and it cannot be moved back.

Sexual lineages have one other option to overcome mutations, recombination. If a gene is mutated in a sexual organism, recombination can occur with it's mate's homologous gene. Thus the offspring will have a nonmutated gene. If a sexual population has several different mutations in various genes in it's gene pool; it is possible through recombination to reconstruct an unmutated progeny. Recombination is several orders of magnitude more common than mutation, so it can easily "take care of" mutations as they arise. Some (most?) biologists think this is why sex evolved (and continues to this day). It eliminates the operation of Mullers ratchet (because organisms can shuffle all the "good genes" in the gene pool into one organism).

In order to understand the paper I will outline in my 2nd post, one must understand one more concept, genetic drift. I'll only explain this briefly.

Genetic drift is caused by a binomial sampling error of the gene pool. In a finite population (as all biological populations are) the gametes contributing to the next generation are a sample of the alleles in the gene pool. As anyone who has any grasp of statistics can tell you; the smaller a sample, the less likely you are to get an accurate description of the population. So, in populations that undergo a bottleneck (a severe reduction in numbers), the sample of alleles going to the next generation is a small sample of the population gene pool. Thus, the frequency of each allele in the following generation will be different in the next generation due solely to chance (binomial sampling error to be specific). [Note: this is assuming natural selection is not operating on the allele in question. Natural selection also changes allele frequencies.] The greater the bottleneck, the more severe the sampling error, or genetic drift, is. [Drift occurs to some degree in all population whether they are bottlenecked or not. The smaller the population, the greater effect drift as.]

Drift relates to Mullers ratchet in the following manner. When a mutation occurs in an asexual lineage, only one organism has the mutation. The rest of the organisms are unmutated. If the mutation is only slightly deleterious, it can increase via drift and eventually the unmutated version of the gene can be lossed. When this occurs, the ratchet has clicked a notch and can't be reversed. (The unmutated gene is lost from the population barring a back or compensatory mutation) Of course, to strictly asexual lineages, there is no such thing as a population. Each organism is it's own species. But, there are precious few strictly asexual organisms in the world. Most asexual lineages find some way to "mix and match" genes with those like them, and (as Deaddog could attest) those not really all that much like them. So, in that case, the population of organisms is meaningful.

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Mullers ratchet in an RNA virus

In this paper Lin Chao propagated 20 lineages of the RNA virus, phi 6. This virus was chosen for two reasons. One, it is asexual. (Actually, it has three distinct regions that can be recombined, but recombination can not occur within these regions.) And two, it has a mutation rate several orders of magnitude higher than similar DNA viruses. (In addition, DNA viruses reproduce sexually.) All 20 lineages derived from a single parent virus.

In each lineage he subjected the virus to 40 growth cycles. Each cycle consisted of picking a single virus and growing up a population of 8*10^9 viruses from it. So, the virus was subjected to 40 bottlenecks to intensify drift. If the single virus chosen contained a mutation, the mutation could not be rectified. The ratchet had clicked a notch. (Intensifying drift corrected for the fact that a small amount of recombination is possible in this virus as I mentioned before.)

At the end of the forty cycles he measured the fitness of each of the 20 lineages (compared to the original parent virus). (Fitness of each lineage was measured three times.) He found that each of the 20 lineages differed markedly in fitness. One lineage increased in fitness by 6%, all others decreased in fitness. One lineage decreased to 28% of the parents fitness. The average of the lineages was 78% as fit as the parent (the 95% confidence interval did not include 1 (fitness of parent virus)).

The author concluded that the (highly significant/ P=0.0001) decrease in fitness was due to Mullers ratchet. Each lineage continued to absorb mutations it could not repair. Of course the 6% increase in fitness was an interesting result. No real satisfying explanation of that was given. (If Mullers ratchet was assumed to be operating in the past, however, one possibility immediately springs to mind.)

The paper is (IMHO) important because Mullers ratchet looks good on paper, but it had only been demonstrated once before (in ciliates. Incidentally, allowing them then to have sex stopped the ratchet.). Given that it is one of major reasons sex is thought to have evolved, it's nice to have some empirical evidence that the phenomena actually exists.

Reference

Chao, 1990, Fitness of an RNA virus decreased by Muller's ratchet, Nature 348: 454 - 455

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Human evolution

Larry and I recently had a flamewar, er... scientific discussion about evolution in humans. I just saw a paper concerning human evolution in PNAS (Proceedings of the National Academy of Sciences) and thought I would summarize it. This bears only tangentially on that discussion.

The authors of this paper (a bunch of people from Cavilli- Sforza's lab) set out to draw a phylogeny of 5 human populations and determine whether the differences in the populations were due to natural selection or genetic drift. They gathered data on 100 genetic polymorphisms from people from these 5 groups: two groups of African pygmies, Europeans, Chinese and Melanesians. A polymorphism is a trait (in this case a gene sequence) that is variable in a population. For example, eye color in humans is a polymorphisms.

Phylogenies are drawn by comparing gene sequences and assuming that sequences more similar to each other are more closely related than sequences less similar to each other. [For a brief intro into the theory behind this see Li and Graur, 1991, Fundamentals of Molecular Evolution, Sinauer. There's a little more to it than I'm letting on. However, phylogeny construction is (IMHO) so unbearably boring I don't want to get into the details here.] They arrive at a tree that shows the African populations branching off from the others about 100,000 years ago. (Estimating time of divergence assumes a constant rate of mutation - the relationship of the sequences do not. IMHO, it is not a great idea to automatically assume mutation rates are constant.) Next the Melanesian stock split off from the European/Chinese lineage. Then the Europeans and Chinese split. Finally (in the other half of the tree) the two African stocks separated.

This tree, however, has serious problems. I won't get into them but basically there are a series of checks you can run to see if the tree the computer spits out is reasonable. This tree wasn't. For one thing the tree required Europeans to have an incredibly slow rate of evolution compared to the other populations. The authors find this unlikely although they add (are you out there Larry?) that the population explosion due to the agricultural revolution may have frozen drift and slowed evolution in Europeans by 20-25%.

Using some historical evidence the authors make the assumption that the European stock was an admixture of two other lineages. They then feed the numbers back into the computer and get the following tree. The first split is again the African/others bifurcation. Next the Chinese and the Melanesians split off. Then the European population is formed as a hybrid of the Chinese and as yet undifferentiated African stock. Finally the two African stocks diverge. The authors conclude this tree is more reasonable.

Next they tried to determine if the distribution of polymorphisms is due to drift or selection. They did this by calculating the Fst value for each polymorphism. Fst values are a measure of the variation in a subpopulation with respect to variation in the pooled population. (For details about Fst see Hartl and Clark, 1989, Principles of Population Genetics, Sinaeur.) They determined a distribution of Fst based solely on a model of drift and compared that to the numbers they calculated. They rejected the null (P=0.0023). There were too many high and low Fst values (and not enough in the middle, therefore) to be consistent with drift alone. Extraordinarily high values of Fst indicate disruptive selection. Very low values indicate stabilizing selection.

So basically the authors constructed a phylogeny of 5 human groups they felt was reasonable and determined that some of the differences in the gene pools of these groups was due to natural selection. I thought the paper was pretty good although sketchy in some portions. In any case, a reasonable preliminary data set and interpretation.

Reference

Bowcock, et. al., 1991, Drift, admixture and selection in human evolution: A study with DNA polymorphisms. PNAS 88: 893-843

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Double endosymbionts

Chloroplasts and mitochondria are organelles within eukaryotic cells (cells of organisms other than bacteria, which do not have organelles). These organelles have their own genetic material. It has been shown previously that organellar DNA is much more similar to bacteria than to nuclear DNA from eukaryotes. This, and other evidence, led scientists to the now widely held belief that these organelles were once free-living prokaryotic cells that began living in proto-eukaryotic cells and eventually the two types of cells required each others presence for existence. They were obligate endosymbionts. It's worth noting that organelles still reproduce autonomously within eukaryotic cells.

Recently, a paper in Nature provided evidence for a double endosymbiotic event in cryptomonad algae. Several lines of evidence led researchers to conclude this double event had taken place. First, most chloroplasts are double-membraned (one membrane from the protoeukaryotic cell, one from the endosymbiont bacteria). Chloroplasts from cryptomonad algae have more than two membranes. Also, these chloroplasts contain what is called a nucleomorph, a DNA containing structure thought to be the vestige of a eukaryotic nucleus. (Prokaryotes and organelles don't have a membrane bound nucleus, their DNA just "floats free".)

The clincher came when the researchers amplified up regions of the 18S rRNA gene (using PCR). They found two different length sequences that they called Nu and Nm. Nu they believe to be from the nuclear DNA of the algae and Nm from the nucleomorph (they are still trying to get rigorous proof of this.) The two sequences were very divergent. The Nu was similar to nuclear DNA from amoeboid protozoans and the Nm sequence is similar to red algae. The authors conclude that cryptomonad algae is a chimera of two endosymbiotic events. First a endosymbiotic event in which red algae was formed, then this eukaryotic red algae being taken into a protozoan creating the crytomonad algae.

Reference

Douglas, et. al., 1991, Cryptomonad algae are evolutionary chimaeras of two phylogenetically distinct unicellular eukaryotes, Nature 350: 148-150

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Some data from the rockhunters

Hey everyone! Here's post number nine in my series. In this one (which should be short) I summarize a couple of paleontological papers. Since I'm not a rockhunter myself, I won't give too much detail.

The first paper is a report from Science by Jeram, et. al. In it they describe fossils of land animals from the Silurian. They found an arachnid (spider) and two centipedes. The kicker of the paper was that land was not supposed to be colonized by animals by the Silurian. But, finding predatory arthropods indicates a stable ecosystem containing animals much sooner than expected. [Aside to the good guys; isn't it nice to have a theory that is enriched, rather than embarrassed, by new data] This finding even made it's way to the popular press, my mom sent me a newspaper clipping (probably KC Star - I can't remember) about it.

The second paper appeared in Nature and was authored by Pilbeam et. al. In this paper they describe two recently found Sivapithecus humeri and they discuss the hypothesis that it was closely related to the genus Pongo. The upshot of the paper is, previous skull specimens of Sivapithecus indicated that it was probably closely related to Pongo, however, the newly found humeri are not at all similar to Pongo The authors conclude that the data is not sufficient to make a decision at this time.

If you want the full, gory, jargon-laden description, plus the photos of these fossils check out the refs. There is also an article about evolution of arthropods in that same issue of Science, but it's not really that interesting (to me at least).

References

Jeram, et. al., 1990, Land Animals in the Silurian: Arachnids and Myriapods from Shropshire, England, Science 250: 658 - 660

Pilbeam, et. al., 1990, New Sivapithecus humeri from Pakistan and the relationship of Sivapithecus and Pongo, Nature 348: 237 - 238

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Corn, caterpillars and wasps

Well, I haven't heard any creationists on this board claim recently that there is no evidence for evolution, but I'll keep this series going since all the mail I've got concerning it has been favorable. I'll summarize here a paper from the most recent issue of Science.

In this paper, Turlings, et. al. investigate the interactions of corn plants, caterpillars and parasitic wasps. The wasps parasitize the caterpillars that, in turn, eat corn. The authors found that corn, when eaten by caterpillars, releases chemicals (terpenoid volatiles) that attracts wasps.

To determine what stimulus caused the release of these chemicals Turlings tested the following leaf types with respect to their ability to attract wasps: 1) leaves that caterpillars had eaten 2) leaves that were mechanically damaged (cut w/ razor blade) 3) leaves with caterpillar saliva on them. Note that the first type of leaf would have both mechanical damage and caterpillar saliva on it. It had been previously established that wasps were attracted by terpenoids.

The authors found that the first type of leaf (caterpillar chewed) attracted the most wasps. They concluded that a combination of damage and saliva were required to efficiently attract wasps.

In addition to measuring wasp attraction, they analyzed the chemicals released by the corn by gas chromotography. This was to insure that terpenoids were indeed being released. They were, so Turlings concluded it was the terpenoids that was attracting the wasps (and these terpenoids were only produced in response to caterpillar damage).

It had previously been shown that plants produce chemicals to ward off grazers. Most of these chemicals, however, work in a straightforward fashion. Bug eats chemical; bug dies. This is one of the first papers to demonstrate a chemical defense that works in a more roundabout way. Bug eats plant. Plant releases wasp attracting chemical. Wasp eats bug.

The authors do not discount the possibility that the terpenoids may also harm the caterpillars in some direct way. But, the primary value of the terpenoids to the corn is its ability to attract a predator of the caterpillar. There is more to the paper, but I just wanted to hit the highlights.

In the recent Nature there are a couple of very interesting articles (about wrens). I'll try to get around to summarizing them this week sometime.

If you are wondering what this has to do with evolution ask yourself this question, how did this system arrive at this point? Remember Steve Timm claimed that creationists (some? most? all?) believe that before "the fall" there were no predators.

It is easy to construct a plausible way for this system to reach the point it is now at given evolutionary theory. I don't see how you can given a creationist scenario. Both the corn and wasps must change in the interim between the supposed fall and present time. Creationism provides no mechanism for change.

Reference

Turlings, et. al., Exploitation of Herbivore-Induced Plant Odors by Host-Seeking Parasitic Wasps, Science 250: 1251 - 1252

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Observed speciation

Kathleen Hunt(jespah@milton.u.washington.edu) writes:


6) "Though evolution has been studied for years, scientists have never observed a single species evolving". So what? Evolution has been studied for just over a hundred years. Speciation takes *LONGER* than just over a hundred years. If you just study evolution for about a hundred years, all you would expect to see is microevolution within species, and perhaps the splitting off of subspecies who might be on the road to speciation. Scientists *have* observed both of these events.
Creationists seem to want to define species evolving solely in terms of speciation. Microevolutionary change doesn't seem to fit their bill as evolution. In fact I just responded via email today to some guy who didn't understand how the English moths had anything to do with evolution. (To be fair, I'm not sure if he was a creationist or just didn't get my point.) As Kathleen pointed out, evolution has been observed (microevolutionary changes and the beginnings of speciation). Most creationists (as well as many evolutionists, perhaps) would be surprised to know that speciation has been observed!
In the genus Tragopogon (a plant genus consisting mostly of diploids), two new species (T. mirus and T. miscellus) have evolved. This occured within the past 50-60 years. The new species are allopolyploid descendents of two separate diploid parent species.

Here's how it happened. The new species were formed when one diploid species fertilized a different diploid species and produced a tetraploid offspring. This tetraploid offspring could not fertilize or be fertilized by either of it's two parent species types. It is reproductively isolated, the definition of a species (well, the most common definition, at least.) The paper I have corresponding to this are great. One new species, T. mirus has arisen at least three separate times.

So, speciation has been observed in case they bring up that again. In fact, it happened instantly in this case. Plants are amazingly plastic in regards to genetics, so it really isn't all that surprizing that the first (as far as I know) observed speciation event would be something like this in plants.

References

Soltis and Soltis, 1989, [the title is mangled on my photocopy], Amer. J. Bot. 76(8): 1119 - 1124

Roose and Gottlieb, 1976, Genetic and Biochemical Consequences of Polyploidy in Tragopogon, Evolution 30: 818 - 830

(The Soltis paper looks at chloroplast DNA, the Roose paper examines allozyme data. Both are, IMHO, fairly decent papers.)

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Exons and "The Curly Shuffle"

I've mentioned the term exon shuffling in several of my posts, so I might as well get around to explaining what the hell I'm talking about. This is especially true since there is a paper in this weeks Science about the "Exon Universe" that will be the second part of this article. In this introduction to the paper, I'll explain a little about gene structure and what exon shuffling is. (Keep in mind that DNA codes for RNA which codes for protein)

The bacteria E. Coli was used in most of the very first molecular genetics experiments. When the first genes were sequenced from it, it was found that all the information for the protein lay in one continuous stretch (an open reading frame (ORF)). It came as a bit of a surprise when the first eukaryotic genes were sequenced and this was not the case. It seemed typical eukaryotic genes contained several open reading frames of DNA interrupted by sequences of DNA that did not code for anything. The coding regions were dubbed exons and the intervening sequences were dubbed introns.

It was soon found out that exons commonly coded for a functional domain or subunit of a protein. In other words, that introns often separated useful "building blocks" of proteins. Of course this led to speculation that, perhaps exons could be duplicated, deleted or "mixed and matched" from an existing gene to create a whole new gene with a new function. If a whole gene was duplicated for instance (this is fairly common), one gene could continue doing its job while the other is free to evolve a new function by swapping exons with other duplicated genes. This is what exon shuffling refers to.

Of course, this would be a great way to gain new useful genes and their corresponding proteins in a hurry. And, it wasn't too long before exon shuffling was confirmed to have happened. Two genes, low density lipoprotein (LDL) receptor gene and the epidermal growth factor (EGF) were shown to be mosaic genes. Although they were functionally unrelated, they shared a few common exons.

It may seem a bit farfetched to those who don't know much about molecular genetics that exons could just whiz all over the genome and conveniently plunk down in a useful place. In fact there are plenty of mechanisms for moving DNA from one part of the genome to another. I'll mention a couple.

One is gene conversion. This is a phenomena by which one stretch of DNA "erases" another stretch and copies itself in it's place. The mechanism is well known, but I don't have time to explain it. Any molecular bio text will have that info.

Another is transposition. This is when a stretch of DNA simply excises itself from one part of genome and moves itself to another. Transposons are pieces of DNA that do this. Many biologists (including myself) tend to think of them as molecular parasites. They don't do any good to the cell or organism. But since they move around the genome so much, it's hard to get rid of them. Transposons carry a few genes with them, usually only the genes required for their own movement.

If two transposons surround a stretch of DNA, they can carry that stretch of DNA along next time they both move if they move as one big unit.

These processes aren't directed or cognizant in any way, so an exon doesn't know to get shuffled to the right place. In fact, often an exon (or transposon) will plop down in the middle of a functional gene. The result is one dead organism. But, occasionally a good rearrangement will take place. It's a hit or miss phenomena.

So, theres an explanation of exon shuffling and a bit of info as to how it could happen. Tomorrow, I'll try to post a summary of the paper in Science.

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The universe of exons

O.K., here's a summary of the paper. It's not that long really, but very dense. I'll summarize the high points and just warn you that I'm leaving out some stuff.

The paper is called "How Big is the Universe of Exons". Recall that an exon typically encodes on functional domain of a protein (for example a DNA binding domain). Duplicate genes can "swap" introns and quickly evolve new proteins. A homologous DNA binding exon, for example, might be found in many entirely unrelated gene, indicating it was imported intact from another gene. This "prefab" construction of genes is called exon shuffling.

The authors of the paper made the following assumption in the beginning of the study. Since introns (the sequences that intersperse between exons) are found in all eukaryote taxa and they typically are in the same place in homologous proteins, the intron/exon structure of genes must be ancestral. The competing point of view is that introns are rather new and spread through all taxa as transposon-like elements. Some intron placement lends credence to this view, but, IMHO, most introns were probably present in the progeonote (latest common ancestor to all living organisms). Some introns invaded later. As an aside I will mention that bacteria do not contain introns, some biologists take this to mean that they "dropped" their introns to streamline their genomes. Others take this as proof that introns invaded after the divergence of prokaryotes and eukaryotes. For what it's worth, I favor the first hypothesis.

The authors then set out to calculate how many exons would it take to account for all the proteins we have in all organisms today. This assumes modern day proteins did not each evolve slowly but were assembled by throwing together domains until something worked.

To do this they plugged their computer into the Genbank and EMBL databases and basically looked at every gene ever sequenced (a bit of an exaggeration). They then went through and narrowed the list of sequences down to non-homologous genes and non-homologous sequences within genes. For example, if the alcohol dehydrogenase sequence from one species was used, the sequences from other species were thrown out. Likewise, if a gene had more than one domain that was identical (not uncommon) the "extra" domains were deleted. All this was done in an attempt to eliminate duplicate exons from known homologous sources. (Note: all sequences were first "transcribed" from DNA sequences to amino acid sequences via the universal genetic code - this was done by computer)

Much mathematical/statistical/computer simulation mayhem followed 8-) I'll supply the reference for those who want to wade through the gory details. (I'm still mulling over some of the analysis) Basically, however, what they did can be explained as followed. From the sample of genes they took out of the database, they made pairwise comparisons and checked how many identical exons they had. They used this sample number as an estimate of the total of identical exons in the population (all organisms). They concluded that between 1000 and 7000 exons were needed to create all the proteins we see today. A rather small number, all things considered. (Boy, don't you love hand waving. I think I almost broke my wrist 8-) At least now I understand the appeal of creationism ;-) )

At the end of the paper a considerable amount of time is spent examining all the possible assumptions and consequent errors that could be included in the study. They are rather numerous, but the authors do their best to deal with them. They range from the chances of forming two identical exons by chance to homologous exons diverging in amino acid sequence, but not function. Some problems would cause the estimate of total exons too small, others would cause the number to be too large.

Well, it certainly was an interesting paper; I'll give them that. And, I would guess that they are probably not off by too many orders of magnitude 8-)

Reference

Dorit et. al., 1990, How Big is the Universe of Exons, Science 250: 1377 - 1382

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Introns of ancient origins

This is number 13 in my series of postings about current research in evolution. I'll summarize two papers from a recent issue of Science, both of which basically reported the same finding. I'm kind of pressed for time today, so this will be a bare bones summary. But, as always, I'll supply the references.

First a bit of background. In eukaryotes, (basically all organisms except bacteria) genes typically are not found as a single uninterrupted reading frame. There are sequences interspersed within the coding region of genes. They are excised after the DNA is translated into RNA.
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Fossil Evidence:

Perhaps the classic argument against evolutionary theory comes from the fossilized remains of organisms found to have existed throughout time. If purely natural evolution has actually occurred in the past and all living organisms share a common ancestor then one ought to find the fossilized transitions between one form and another in the fossil record. However, it has been well known since Darwin's time that plausible "transitional fossils" rarely exist:

"... The number of intermediate varieties, which have formerly existed on the earth, (must) be truly enormous. Why then is not every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any such finely graduated organic chain; and this, perhaps, is the most obvious and gravest objection which can be urged against my theory." (Darwin, C. (1859) The Origin of Species (Reprint of the first edition) Avenel Books, Crown Publishers, New York, 1979, p. 292)

Out of tens of thousands of species known from the fossil record, only a few are claimed to be Darwin's missing transitional forms. However, a close analysis of these few fossils (commonly cited ones are Archaeopteryx (a bird), Ambulocetus (a land mammal), and Acanthostega (an amphibian)) reveal that they do not shed any light on the origin of the important features of their respective groups. Harvard paleontologist Stephen J. Gould said,

"The absence of fossil evidence for intermediary stages between major transitions in organic design, indeed our inability, even in our imagination, to construct functional intermediates in many cases, has been a persistent and nagging problem for gradualistic accounts of evolution." (Stephen J. Gould, 'Is a new and general theory of evolution emerging?' Paleobiology, vol 6(1), January 1980, pg 127)

Gould proposed a theory called "Punctuated Equilibrium" which is meant to account for the lack of transitional forms, saying we don’t find transitional forms because transitions didn’t have a chance to be fossilized. But punctuated equilibrium does not fit with the workings of genetics--too much biological complexity must be built with far too few rolls of the dice. The lack of transitional forms remains unaccounted for and is a strong evidence against evolution. See Phillip Johnson’s, "Darwin on Trial" for a good account of problems with the fossil record.
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Ik ben blij dat het phenomeen evolutie aan alle kanten rammelt.
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Paley argued that we can draw the same conclusion about many natural objects, such as the eye. Just as a watch’s parts are all perfectly adapted for the purpose of telling time, the parts of an eye are all perfectly adapted for the purpose of seeing. In each case, Paley argued, we discern the marks of an intelligent designer.

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Opsin Genes

ob Bales brought up an interesting topic in a recent post (well, it was recent when I started writing this). The topic is "evolution and color vision". Bob is apparently under some misconceptions either about color vision, or at least what evolutionary theory might predict about it. In a series of four posts beginning with this one, I want to ramble on and on about some of the background you might want to know if you were going to make some meaningful statements about evolution and color vision.

I'm going to start by describing a tiny fraction of what's well known about the molecular biology and biochemistry involved in visual transduction. If you're familiar with the topic, you may want to skip to the last couple of paragraphs in this post where I get to some data illuminating the evolutionary origins of the visual pigments. In followup posts I'm going to describe a bit of comparative psychology of color vision (to buttress the point that color vision systems are not all the same). In a third post I'm going to discuss some comparative anatomy, with a focus on the visual systems of mammals. I intend to demonstrate how comparative anatomy makes sense in light of what the fossil record tells us about the history of mammalian evolution. Finally, in a fourth post I will outline some of the steps that would be required in order for an organism to acquire color vision, with a discussion of how reasonable it is to suppose that such systems could evolve multiple times.

I no longer have access to Bob's post, but as I recall he was making some sort of statement that the distribution of current species which have color vision is at odds with what an evolutionary biologist would expect.

Let's dissect this claim with a little bit of thought and a look at some data. In the first place, I got the distinct impression from Bob's post that he thought "animals with color vision" should form a monophyletic group. This is absurd. In this context, saying that an animal has color vision is like saying an animal has a tail. Suggesting that two animals (say bees and humans) should be considered more closely related to each other than two others (say cats and humans) on the basis of the extent of their capacity for making color discriminations is similar to suggesting that two animals (say salamanders and lobsters) should be considered more closely related to each other than two others (say salamanders and frogs) just on the basis of which animals have tails. I'm not going to leave this discussion at this point, but I'll postpone the rest of it for my second post while I begin with some basics.

What does it mean to say that an animal has color vision? The term color vision is used in different contexts with somewhat different meanings, but from our own perspective of what it means to see in color, the best definition would go something like:

An animal has color vision if it has the capability of discriminating lights (scattered light as well as light sources) on the basis of the lights' spectral content, even when those lights are of equal subjective brightness.

The front end requirement for such a system is that the animal must have at least two different spectral classes of receptor, where each class is defined by the sensitivity of the receptor to light as a function of wavelength. This often leads to a looser definition of color vision: an animal is declared to have color vision if it has at least two spectral classes of photoreceptor operating at the same time.

Although there are a variety of ways in which different receptor classes could be constructed, it seems that extant organisms use only one.

The first step in the transduction of light energy to a neural signal is the light-induced isomerization (change of shape) of a chromophore, specifically a vitamin A derivative. Each chromophore is bound to a membrane protein called an opsin. The main function of the opsin is to change shape after light absorption triggers the isomerization of the chromophore: the opsin is an enzyme that is activated by the chromophore's isomerization. However, because of the linkage between the opsin and the chromophore, the opsin also serves to tune the wavelength dependence of the light induced isomerization reaction in the chromophore. That is, the chromophore's sensitivity to light at a given wavelength is established in part by the opsin--different opsins (i.e. opsins with different amino acid sequences) bound to identical chromophores will have different absorption probabilities at each wavelength. The result is that photoreceptors which express the gene for only one type of opsin will form a different class than photoreceptors that express a gene coding for a different opsin. Although there are other mechanisms that animals could use to differentiate photoreceptor classes (most notably some animals use more than one chromophore, and many vertebrates have colored oil droplets that screen individual receptors) it seems that the expression of only one of their possible opsin coding genes in each receptor is the mechanism that all animals use.

Now we have to throw in a slight wrinkle. In a vast majority of vertebrates, there are two different sets of photoreceptors, one that operates during the day and another that operates in the dark. Most people are probably familiar with the distinction between rods and cones--rods mediate night vision, cones day. At night when the number of photons around is low, visual systems don't go to such fancy lengths to discriminate the light's spectral content, so there is generally only one class of rod in any given animal (at least some frogs are exceptions to this rule). For all intents and purposes, none of us have color vision when we're dark adapted. Thus with respect to vertebrates, the discussion of photoreceptor classes above was more specifically a discussion of cone classes.

Here we'll get to some interesting stuff by looking at the opsins for which we have the most data. DNA and peptide sequences for various opsins have been determined. In 1990, all of the then known amino acid sequences were compared in order to infer a phylogeny for the opsin molecules. These sequenced proteins consisted of four different opsins from drosophila, one from octopus, four from human (one rod, three cone) and one rod opsin each from chicken, sheep, cow, and mouse. All of the opsins have similar sequences, but any good evolutionary biologist could tell you that some should be more similar to each other than to others. Would anybody like to draw their guess at the phylogeny determined for these thirteen proteins? (Hint, it appears that all opsins derive from a very ancient protein, since it has homologs in bacteria as well as in both invertebrates and vertebrates. (I've recently stumbled onto a reference that claims that vertebrate rhodopsin and bacteriorhodopsin are not part of the same gene family. I'll reserve judgement until I've read more than just the abstract of the paper. E-mail me if you would like to see the reference yourself.) Amongst vertebrates, the rod opsin seems to be the most conserved; cone opsins have arisen principally by duplication and subsequent mutation of the rod opsin gene.) Suffice it to say that these known opsins are not distributed in a mix and match fashion as one might guess a designer would have distributed them. If you'd like to see the phylogeny, you can look up the Goldsmith paper listed in the fourth post in this series. Alternatively I guess I could make an ASCII representation of it.

It should also be noted that many humans carry more than one copy of the middle wavelength-sensitive cone opsin. As this is grist for the evolution of color vision mill, we're literally ripe for the addition of a fourth cone class. (This probably won't happen, though, because people with a fourth cone class will be constantly trying to readjust the color on television sets. As a result of that such people will be highly selected against in bars the world over :-)

Since 1990, a few other opsins have been sequenced, specifically opsins from a variety of monkeys. I don't know as that they've been compared with the others, but I'm willing to predict where they should fit into the picture. It's nice to have a theory that lets you do that. (Since I wrote this last paragraph, I've seen another phylogeny that I think had more than twice as many opsin sequences as my best current reference. As far as I know, that work is still in press, and I no longer have access to it. From what I saw, though, the creationists have even more reason to fold their hand on this one now than they did two years ago...)


Comparative Psychology

Prior to the advent of some nifty techniques in molecular biology, people had to use less direct methods of classifying photoreceptors. Among these methods are: direct measurement of the absorptive properties of individual receptors, measurement of the electrical responses of cells to monochromatic lights, and the conditioning of learned behaviors. Thus even without molecular biology, we knew (and know) a lot about the pigments underlying color vision systems.

Based on this sort of information, it's clear that most vertebrates have at least two cone classes. In fact, many birds, turtles and fish have four or five. Many invertebrates are similarly well endowed, and last I heard, the mantis shrimp was the winner of the contest of who has the largest number of photoreceptor classes. Given that coral reef animals and tropical birds often appear very colorful to us, it's not surprising that they have well developed systems of color vision. That different animals have different numbers of receptor classes already tells us that color vision systems are not all equivalent (as Bob might have us believe). If we restrict ourselves to animals which have the same number of receptor classes, might we expect that their color vision systems are equivalent?

The answer is a resounding no. Let's compare the color vision systems of two animals that both have three photopic (e.g. active under bright illumination) photoreceptor classes. One is the human, the other is the honey bee (specifically the worker--I don't know how the other castes are endowed). Does anybody here think that what a bee sees when it looks at a rainbow has the same appearance as what we see? We'll ignore optical polarization (which the bee is sensitive to and we're not) and focus on what we can infer about "color" based on, among other things, our knowledge of the bee's receptor classes. To begin with, at the inside of the rainbow where the violet-appearing light fades off to invisibility for us, the bee will still see more rainbow. On the outside, where we see red, the bee would see nothing for although bees have an ability to see what for us is UV, we have the ability to see what bees might call infrared.

Now picture that rainbow: what you see appears to have discrete bands of color. Don't for a minute think that those bands arise from there being anything discrete about the radiation emanating from that patch of sky. If you measured the radiation with a spectrophotometer, you'd find that the wavelength of maximum intensity as a function of the radial distance across the rainbow would decrease smoothly and monotonically from the outside to the inside of the bow. The apparent discreteness is an artifact of our photopigments (chromophore + opsin) and the neural processing of our photoreceptors' outputs. The bee too would probably see discrete bands (We can't ever really know how the world appears to a bee, but given what we can infer from doable experiments -- I actually chose the bee in part because its color vision has been studied about as much as any other animal's, excluding the human's -- the supposition that it would see discrete "color" bands from a rainbow is reasonable.) However, just as the outer and inner borders would be in different locations for us and bees (as described in the preceding paragraph), the borders of each "color" would be placed differently by the bee as well.

I can't claim that we have a good handle on why different animals have different visual pigments. There are some cases that are well understood--most notably it was predicted some 20 years before verification that marine fish that live just above the aphotic zone would have only one pigment, and that that one pigment would have a maximal sensitivity down around 450 nm (for us light at this wavelength would appear blue). It makes sense that if there isn't much light around, an animal's photoreceptors will be adapted to respond most strongly to the wavelengths of light most readily available. Bioluminescent fish and insects also tend to have pigments that are adapted for maximal sensitivity to the wavelengths of light emitted by their photophores (the molecules responsible for the emission of light e.g. from the abdomens of fireflies). The specifics of what selective advantage other pigments in other environments might convey are still somewhat mysterious (See the Lythgoe and Partridge paper listed in the fourth post of this series for a discussion of the topic).

One thing is clear, however. The best known predictor of what sort of pigments will be expressed by any given animal, is the pigments expressed by its nearest living relatives. To an evolutionary biologist this makes a lot of sense, of course.

There are a lot of other differences (or similarities) between manifestations of color vision systems in different animals. I've chosen to stick to a discussion of pigments here partly for simplicity, and partly because the straightforwardness of analyzing retinal receptors makes this the facet of color vision about which the most data is available. The point of this post is to say that it makes no sense to use the presence or absence of color vision in determining a phylogeny. If you want to be serious about asking what color vision and evolution have to say about each other, you have to ask specific questions about what sort of color vision different animals have.


Mammalian Deficits

In Bob's post, it was suggested that among mammals, color vision is more or less exclusive to primates. This isn't quite correct. In fact there are many other mammals with color vision. For example, diurnal squirrels and tree shrews have each been demonstrated to have at least two photoreceptor classes, and behavioral studies indicate that each meets the strict definition of color vision (the first definition in the first post of this series). Recent finds have also indicated that some rodents are sensitive to ultraviolet light, suggesting that they have a previously unknown class of photoreceptor. However, color vision systems do appear less frequently and with less complexity (i.e. with fewer photoreceptor classes) amongst species of mammals relative to species of most other classes of animal. To understand why this might be so, let's examine the history of mammalian evolution as evidenced by the fossil record, and conciliate that information with some comparative anatomy.

The lineage of animals which joins reptiles and mammals is often touted here as an excellent example of a transitional series. One detail that might seem surprising to people is that this transition occurred at the beginning of the Mesozoic era--the same time during which other reptiles were transitioning into dinosaurs. It's not quite right to say that mammals replaced dinosaurs at the beginning of the Cenozoic era, because mammals existed alongside of dinosaurs during the dinosaurs' entire "reign". However, during the Mesozoic era, dinosaurs and other reptilian cousins (e.g. pterosaurs, plesiosaurs and ichthyosaurs) were an extremely diverse group which occupied most of the available niches. The bush of life had only a small twig representing the lineages that would later branch out into all of the mammalian forms currently extant. Mesozoic mammals were small rodent-like creatures that were most probably nocturnal.

Note that the last paragraph is based only upon what we can glean from the fossil record. If current species arise from the descent with modification of pre-existing species, one might predict that the above inferred history of mammals would leave clues in contemporary mammalian anatomy. Oddly enough such clues exist.

You may recall from the first post in this series that pretty much all animals are "color-blind" in the dark. Consequently, if an animal is only active at night a color vision system would be of little use, much as eyes are of little use to cave fish, moles and other animals which live in the absence of light. So if modern mammals are just descendents of the animals whose fossilized remains are found in Mesozoic strata, you would expect that this would be reflected in the makeup of their retinas. Lo and behold, this expectation is born out quite well.

First off, comparative anatomy indicates that most mammals don't have well developed color vision systems not because their line didn't get around to developing it, but more likely because after our ancestors evolved color vision it became superfluous and was lost. The color vision of primates is not strictly homologous to the color vision of fish, birds, turtles, etc. Much of the machinery used for primate color vision arose independently long after similar systems developed (without being lost) in other vertebrate lineages. At this point the wary creationist might say, "Aha! So primate color vision doesn't fit into the mammalian scheme, and could be construed as evidence of a creator--in developing primates, the creator used a feature similar to what he'd used in those other so-called 'lineages'". I urge anyone who might think this to look more deeply into comparative anatomy. I will only briefly describe a few relevant features here.

Color vision is mediated by cones, so named because of the shape of the receptive part of the cells. If the history of mammalian evolution described above were correct, you would expect to find significant differences between mammalian cones and the cones of other vertebrates. (The initial definition of "cone" vs. "rod" photoreceptors has some kinks, because it is apparent (based on criteria other than the shape of the receptive part of the cell) that some photoreceptors that appear on first glance to be homologous are actually analogous. For example, the "rods" of nocturnal geckos (a type of lizard) are most likely homologous to the cones of other animals--geckos did the opposite of mammals. In their development, geckos went through a strictly diurnal phase, and hence lost some of the adaptations for nocturnal vision. They subsequently became nocturnal again, and thus their cones faced some of the same adaptive pressures faced by the rods of other vertebrates.) Whether or not you expect it, this is exactly what has been found. There are several features that are quite common to the cones of non-mammalian vertebrates, but that are completely lacking in mammals. (As most of you might guess, there are exceptions to the "complete lack" of the characters I'm about to describe. I'll leave it as an exercise to the reader as to which animals are exceptions. I'll tell anyone who guesses and provides with their guess a rationale for why they guessed what they did. That is, if you understand and accept evolution, you would predict that if there are exceptions, they will be found in particular animals. If you don't understand or don't accept descent with modification as the origin of current species, I really would like to know what sort of reasoning you might use to guess at the exceptions.)

Many vertebrates have oil droplets at the bases of the light sensitive parts of their photoreceptors. These oil droplets often have pigments in them that absorb (i.e. filter out) some of the light that would otherwise stimulate the cell. What this does is to modify the spectral sensitivity of the photoreceptor bearing that droplet. This feature is not found in mammals.

Many vertebrates have double cones--two cones that are joined along their long axes by tight junctions, gap junctions or both. Nearly all classes of vertebrates have some variety of this form of receptor in their retinas. This feature is not found in mammals.

The photoreceptors of many vertebrates perform a sort of circadian dance. During the day, the rods are extended on long stalks so that their sensitive parts are buried in a layer of pigmented epithelium. This epithelium shields the rods so that very little light reaches them from the sides, and the cones basically shield them from axially propagating light. At night the cones are extended out into the pigmented epithelium, and the rods are contracted back to where the cones were during the day. This feature is not found in mammals.

The conclusion that might be drawn from the above is that there are many features of ancestral retinal anatomy that were retained in most classes of vertebrates, but lost in mammals. Elaborate color vision is just one such feature. The phylogenies of the opsin molecules that I discussed in the first post of this series suggest that mammals have always retained two cone pigments (a survey in 1981 indicated that there aren't any vertebrates with only one cone pigment), but any mammals that, like us, have more than two pigments (re)gained the third relatively recently (for us probably around 63 million years ago). [For those from sci.bio, this was why I was suggesting that squirrels might be trichromatic--I'm not willing to climb out on that limb now. Our short wave-sensitive or "blue" cone is probably homologous to the UV cone of other (i.e. non-squirrel) rodents. One of the inferred pigments in the dichromatic squirrels has about the same absorption spectrum as our short wave cone, so there isn't any reason to suppose that the squirrel has a third. That is, it is reasonable to conclude on current evidence that the UV sensitive rodents have the same cone classes as the squirrels, only their short wave pigment has been shifted to absorb even shorter wavelengths than those of most other mammals.]


How to See Red

In this final segment I'd like to address some of the probable steps required in the formation of a color vision system. I do this in an attempt to circumvent an argument via lack of imagination about the improbability of such a system arising more than once. The generation or elaboration of color vision systems is not a terribly complicated process (at least at the periphery).

Let's presume that we're starting with an organism that already has an eye of some sort. The first step towards a color vision system is the need for at least two visual pigments. It should be obvious that the addition of a pigment would be of immediate advantage even if the new pigment was expressed in the same cells as the older pigment(s). The reason is that there are some wavelengths of light where the new pigment will respond more strongly than the old, so the addition of a pigment will increase the animal's sensitivity over those wavelengths.

The next step (conceptually anyways--it may be that this and the first step typically occur simultaneously) is the sequestration of the new pigment into a discrete population of photoreceptors. (By discrete, I don't mean spatially. I just mean that each photoreceptor should express only one opsin.) The advantage that this provides comes in the form of visual contrast. The lowest level of visual information processing is the recognition that something is different about a given region of space--i.e. that there is food or a predator "over there". To perform this function in habitats that are rich in light of particular wavelengths (the short wave "blues" underwater, or the mid wave "greens" of the tropical rainforest) it's best to have at least two pigments, one matched to the dominant wavelengths and one offset from those wavelengths. With the matched pigment, non-reflective objects have high contrast as dark areas on a bright background. With the offset pigment, reflective objects will apear bright against a darker background. Except in some extreme conditions (i.e. just above the aphotic zone for marine environments) the background probably isn't constant enough for that simplistic analysis to hold, but it's easy to imagine that if an animal has more photoreceptor classes it has a greater chance that one of them will allow for the visibility of a given target under a given set of background conditions.

(Note that it's not yet clear how the expression of photopigments is regulated in individual cells, but because of its accessibility, the retina is frequently used in studies of developmental neuroanatomy. Experiments with transgenic animals have already given us some key pieces of information about the regulatory mechanisms that determine what sort of photoreceptor a retinal precursor cell will become. Immuno- histochemistry has also been used to show that the fate of a cell, i.e. what sort of cell it will become, is established long before morphological differentiation is apparent. This is a hot area where the rest of this century is sure to see incredible advances in our knowledge base.)

The next step is the development of neural wiring in the retina that segregates the signals from one population of cells from those of the other(s). (Oddly enough this isn't necessary for the previous advantage, although as I'll describe below, there is good reason to suppose that these two steps occur simultaneously as a result of the mechanisms of neural development.) The advantage of this is that it allows the animal's retina to "draw" contours around an object (i.e. to place "color" boundaries on the visual scene).

The last phase in the development of color vision is the arrangement of wiring in the brain that allows an animal to segregate and classify objects according to their "color" (i.e. according to how well the object stimulates the different receptor classes). The advantage of this adaptation is that it allows the animal to classify objects according to "color". For example, it has been argued (although to me this is a just so story and may not be correct) that color vision and the expression of pigments in fruit co-evolved. That is, it is to the plants' advantage to have its fruit remain un-eaten until the seeds are ready for dispersal, so the color change in ripening fruit is a signal that the plants are sending to the animals. In turn the animal gets the greatest benefit from eating the ripened fruit, so it is to the animals' advantage to recognize when the fruit is ripe. The sort of comparison necessary for discriminating ripe from unripe fruit is easy if, for example, objects which reflect a lot more long than short wavelength visible radiation bring about a particular quality of sensation (e.g. what we call "red").

The point of the above was to make explicit that even if an animal were to develop color vision in steps, it's not hard to imagine a sequence of steps in which each step confers some advantage which would cause that step to be selected for. However, there's a beauty in the way that nervous systems are constructed which might lead you to expect that rudimentary color vision can arise in a "color blind" animal in only one or two steps.

The addition of a new pigment arises from a gene duplication followed by mutation of one (or both) of the copies. As indicated in the first part of this series, it seems pretty clear from gene sequence data that this is exactly how new pigments have arisen in us, fruit flies and a couple of other primates. By inference it seems likely that this is a widespread occurrence.

I'll end now with a brief foray into neurobiology. Animal nervous systems, particularly the nervous systems of vertebrates are not "hard-wired" at birth (or hatch or the end of metamorphosis...). Decisions about which nerve cells should be connected to which other nerve cells are made during a long space of time prior to adulthood, and in some animals (though usually to a much more limited extent) even during adulthood. Genetics seem to specify (in unknown ways) some of the gross features of connectivity--for example in mammals the axons of ganglion cells in the eye mostly grow through the optic nerve to a particular group of cells in the thalamus. However, the fine distinctions about, for instance, which ganglion cells connect to which cells in the thalamus are made initially by the formation of a lot of random connections. Many of these connections are then pruned back so that each ganglion cell stimulates only a small subset of the cells it initially connected with. The "rules" governing the pruning back are largely based on correlations in the activity of different cells--if two cells in the retina are generally active at the same time, then they will probably end up being connected to the same cells in the thalamus.

This activity-dependent pruning of connections appears to be the way that "maps" are created in higher brain areas. The best indicator of whether or not two cells in the retina will be simultaneously active, is how close they are to each other in space. Cells in the thalamus thus form a map of cells in the retina according to their activity, and hence their connectivity. Now it's easy to imagine that another determinant of whether or not two cells will be active at the same time is whether or not they are connected to cells which express the same pigment (within the retina, the same rules are followed in the creation of connections, so ganglion cells will preferentially be connected to cells which express the same pigment). So in the thalamus and other brain regions, there will be maps of the different receptor types within the maps of retinal location.

Of course neural development is a lot more complicated than I've described here, but the take home message is that the way that nervous systems develop in growing animals makes it easy to incorporate changes at the periphery. It has to be that way, or our nervous systems would not be able to cope with changes which occur in our muscles and sense organs as a result of growth.

If I've been at all clear, you'll see that once an animal has different photoreceptor classes the rest of the nervous system is already prepared to take advantage of them. An interesting case study in this regard is new world monkeys. In at least one species, two of their opsin genes are (like our mid- and long- wave sensitive opsins) on the X chromosome. The monkeys' expression patterns are different from ours, however, and it turns out that for one (or two depending on how you think about it) class of photoreceptor, the females can express the genes on each X chromosome. The males naturally only have one X chromosome. In the population, there are two types of male (depending on which allele they have on their X chromosome), and three types of female (depending on whether they are heterozygous, or homozygous for one or the other allele). The monkeys' developing nervous systems seem to take advantage of whatever photoreceptor classes happen to be out there in that animal's retina.


Further Reading

I'm sure I've left a lot of things unclear, but if anyone wants to find out more, I can recommend a few references. A good general source for information about neurobiology, with several chapters on vision is:


Principles of Neural Science 3rd Edition, edited by Eric R. Kandel, James H. Schwartz, Thomas M. Jessell, Elsevier, New York, 1991.
An excellent book that treats the principles necessary for appreciating comparative studies of visual systems is:


Lythgoe, J. N. (1979). The Ecology of Vision, Oxford University Press, Oxford (and also Clarendon Press, New York).
After reading that, you'll probably be prepared for:


Jacobs, G.H. (1981). Comparative Color Vision, Academic Press, New York.
and a few papers:


Goldsmith, T.H. (1990). "Optimization, Constraint, and History in the Evolution of Eyes", Quarterly Review of Biology, 65(3):281-322.
McFarland, W.N. and Munz, F.W. (1975). "The Evolution of Photopic Visual Pigments in Fishes", Vision Research, 15:1071-1080.

Hemila, S., Reuter, T. and Virtanen, K. (1976). "The Evolution of Colour-Opponent Neurons and Colour Vision", Vision Research, 16:1359-1362.

Lythgoe, J.N., and Partridge, J.C. (1989). "Visual Pigments and the Acquisition of Visual Information", Journal of Experimental Biology, 146:1-20.
Groetjes
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Oud 07-02-2002, 16:54
legatus
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Developmental Evidence:

Many who took evolution in school probably heard the phrase, "ontogeny recapitulates phylogeny", meaning that evolutionary history is reflected during the growth and develpoment of an organism. A common evidence for this is the alleged presence of fish gills in human embryos during growth. Though humans do indeed have gill-like structures (very different from gills--they're more like small wrinkles in the neck) this classic evidence for evolution has been debunked as it has been shown that it's originator, Ernst Haeckel, faked the data. In fact, comparisons of embryos of humans, fish, chickens, and amphibians show that organisms develop in a way NOT predicted by evolutionary theory. These embryos begin very different, briefly become somewhat similar at an intermediate stage, and then end very different. If ontogeny really does recapitulate phylogeny, and these organisms have a common ancestry, embryos should be similar from the very beginning and grow more different during development. This, however, is not the case, making this a powerful evidence against common ancestry. Again, Jonathan Wells’ book, "Icons of Evolution" is a good reference for this evidence.
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Oud 07-02-2002, 16:55
Demon of Fire
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Citaat:
legatus schreef:
Lang onzinnig creationistisch verhaal.
http://www.talkorigins.org/faqs/archaeopteryx.html
http://www.talkorigins.org/origins/f...ationists.html

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Ben(die creationisten niet vertrouwd, omdat ze bewijzen en theorieen aanpassen naar hun eigen inzicht en dus niet objectief zijn
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Oud 07-02-2002, 16:59
legatus
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Onzinnig?

Jij komt met fossielenbewijs terwijl ik met tegenargumenting kom.

Jij komt met evolutie van visie en ik met ontwikkelingsargumentering.

En het feit dat jij het gelijk als Creationisme afschrijft vind ik wel erg drastisch -- heb je de uitleg van Intelligent Design wel gelezen?
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Oud 07-02-2002, 17:02
legatus
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Als DNA de informatie bezit waar alles uit opgebouwd word waarom is het dan zo onzinnig om Intelligent Design weg te werpen?

De mens komt uit één cel zonder enige informatie en groeide zomaar verder. Wauw, dat is pas een goeie evolutionaire beredenering.
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Oud 07-02-2002, 17:03
Demon of Fire
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legatus schreef:
Onzinnig?

Jij komt met fossielenbewijs terwijl ik met tegenargumenting kom.

Jij komt met evolutie van visie en ik met ontwikkelingsargumentering.

En het feit dat jij het gelijk als Creationisme afschrijft vind ik wel erg drastisch -- heb je de uitleg van Intelligent Design wel gelezen?

Ik heb het verhaal gelezen ja.

Ik stel voor dat je het verhaal over creatnisten gaat lezen. Dan zul je hun werkelijke motieven ontdenkken. Dat is geen wetenschap bedrijven, maar bijbel bedrijven.

Het zijn geen legitieme tegenargumenten, en daarvoor moet je meer over creationisme weten.

Gelukkig is Creationisme praktisch alleen maar een amerikaans phenomeen en wordt de rest van de wereld bespaard.

Groetjes
Ben(die creationisme verracht en vind dat het misbruikt maakt van de wetenschap
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Oud 07-02-2002, 17:05
Demon of Fire
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legatus schreef:
Onzinnig?

Jij komt met fossielenbewijs terwijl ik met tegenargumenting kom.

Jij komt met evolutie van visie en ik met ontwikkelingsargumentering.

En het feit dat jij het gelijk als Creationisme afschrijft vind ik wel erg drastisch -- heb je de uitleg van Intelligent Design wel gelezen?
Er is niemand die heeft gezegd dat er vanuit aminozuur in 1 keer een bacterie is ontstaan.

Dat is de argumentatie van creationisme...*zucht*

Er zijn eerst een tiental tussen-fasen.

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Oud 07-02-2002, 17:05
legatus
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Maar wat is nu de werkelijk reden om creationisme of intelligent design weg te drukken?

Omdat het belachelijk is dat we een beetje hulp gekregen hebben? En dat het universum over triljarden jaren bij toeval een goede combinatie heeft gevonden waar leven uit kwam? Of zelfs een simulatie van leven?

[Dit bericht is aangepast door legatus (07-02-2002).]
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Oud 07-02-2002, 17:08
Demon of Fire
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legatus schreef:
Maar wat is nu de werkelijk reden om creationisme of intelligent design weg te drukken?

Omdat het belachelijk is dat we een beetje hulp gekregen hebben? En dat het universum over triljarden jaren bij toeval een goede combinatie heeft gevonden waar leven uit kwam? Of zelfs een simulatie van leven?

[Dit bericht is aangepast door legatus (07-02-2002).]
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Intelligent Design
Humans, Cockroaches, and the Laws of Physics
Copyright © 1997 by Victor J. Stenger

Preprint of a paper submitted to Creation/Evolution.
Do not reprint without permission from the author.



Other Links:
The Mediocre Universe
This Feb. 1996 Discover magazine article discusses the cosmological hypothesis that our universe is but one of many.
Design and the Anthropic Principle
Creationist Hugh Ross argues that the fundamental constants of nature are so precisely tuned that they could not have occurred without an intelligent designer.

Evolution is Not the Whole Story

s the bankruptcy of creation "science" becomes increasingly recognized, a new catch phrase, intelligent design, has been adopted by those who persist in their attempts to inject creationism into the science curriculum (see, for example, Of Pandas and People, Davis 1993; Matsumura 1995 and Cole 1995 report on attempts to introduce Pandas into schools). Intelligent design is a more subtle term than creation science, one that has far broader implications than the genesis of life on a minor planet in the corner of a minor galaxy. The argument that the material universe resulted from conscious action outside itself can sound convincing, even to those who accept biological evolution as established fact. Many who agree that biblical creation is not an appropriate part of the science curriculum, because it is not science, may not object to including material that argues with greater sophistication that the universe as a whole shows evidence for design.

I can foresee proponents of intelligent design campaigning for science lessons to include statements of the sort we often read today in books and the popular press, that modern physics and cosmology have uncovered evidence for intelligence in the structure of the universe and this intelligence seems to act with us in mind (Rolston III, 1986; Wright, 1992; Begley, 1994). In fact, science has done no such thing. Just as we must continue to educate parents and teachers on the facts of evolution, we must also inform them that science has by no means confirmed the traditional belief in a created universe with humanity at its center.

Indeed, if anything science indicates quite the opposite. Astronomical observations continue to demonstrate that the earth is no more significant than a single grain of sand on a vast beach. While a created, human-centered universe can probably never be ruled out, nothing in our current understanding of cosmology and physics requires it. Furthermore, we are beginning to understand the possible physical mechanisms for the appearance of matter from nothing, and for organization without design.

Evolutionists have successfully refuted the usual argument for design that is grounded on the intricacy of biological life. They have convincingly demonstrated, to any rational person, that complexity sufficient for life could readily have emerged naturally in the primeval chemical stew. However, the processes of biological evolution on earth still depended on the pre-existence, billions of years ago, of the particles and "laws" of physics.

For example, consider the calculation by astronomer Fred Hoyle, often referred to by creationists, that the odds against DNA assembling by chance are 1040,000 to one (Hoyle, 1981). This is true, but highly misleading. DNA did not assemble purely by chance. It assembled by a combination of chance and the laws of physics.

Without the laws of physics as we know them, life on earth as we know it would not have evolved in the short span of six billion years. The nuclear force was needed to bind protons and neutrons in the nuclei of atoms; electromagnetism was needed to keep atoms and molecules together; and gravity was needed to keep the resulting ingredients for life stuck to the surface of the earth.

These forces must have been in operation within seconds of the start of the big bang, 10-15 billion years ago, to allow for the formation of protons and neutrons out of quarks and their storage in stable hydrogen and deuterium atoms. Free neutrons disintegrate in minutes. To be able to hang around for billions of years so that they could later join with protons in making chemical elements in stars, neutrons had to be bound in deuterons and other light nuclei where energetics prevented their decay.

Gravity was needed to gather atoms together into stars and to compress stellar cores, raising the core temperatures to tens of millions of degrees. These high temperatures made nuclear reactions possible, and over billions of years the elements of the chemical periodic table were synthesized as the by-product.

When the nuclear fuel in the more massive, faster-burning stars was spent, the laws of physics called for them to explode as supernovae, sending into space the elements manufactured in their cores. In space, gravity could gather these elements into planets circling the smaller, longer-lived stars. Finally, after about ten billion years, the carbon, oxygen, nitrogen and other elements on a small planet attached to a small, stable star could begin the process of evolution toward the complex structures we call life.

In recent years, creationist theologians, and even a few physicists, have heavily promoted what they claim is a remarkable fine-tuning of the basic laws and constants of physics, without which life as we know it would never have developed (Barrow, 1986; Rolston III). If the universe had appeared with slight variations in the strengths of the fundamental forces or the masses of elementary particles, that universe would be pure hydrogen at one extreme, or pure helium at the other. Neither would have allowed for the eventual production of heavy elements, such as carbon, necessary for life.

Similarly, if gravity had not been many orders of magnitude weaker than electromagnetism, stars would not have lived long enough to produce the elements of life. Long before they could fabricate heavy chemical elements, stars would have collapsed. Only the fact that the gravitational force was forty orders of magnitude weaker prevented this from happening.

In a calculation similar to Hoyle's, mathematician Roger Penrose has estimated that the probability of a universe with our particular set of physical properties is one part in 1010123 (Penrose 1989: 343). However, neither Penrose nor anyone else can say how many of the other possible universes formed with different properties could still have lead to some form of life. If it is half, then the probability for life is fifty percent.

Ignoring this absent link in their chain of logic, promoters of intelligent design put forward the so-called anthropic coincidences as evidence for a universe that was created with humans in mind. I have heard Christian philosopher William Lane Craig make this claim in a debate on the existence of God. In the same debate, Craig contended that the great age of the universe, which dwarfs human history, is in fact a sign of God's plan for humanity because billions of years were needed to allow life to evolve. (Craig evidently accepts evolution). You would have thought God could be a lot more efficient. And Craig did not rationalize why humanity rather than cockroaches was the goal God had in mind.

So as you see, we have a lot more explaining to do after we explain how life developed on earth by natural processes. Even if life evolved naturally on earth with no outside interference, the existence of stars and planets, quarks and electrons, and the very laws of physics themselves can be presented as evidence for intelligent design to the universe. Furthermore, given the egocentrism that seems to characterize the human race, convincing people that the universe was designed with them in mind is as easy as convincing a child that candy is good for him.

Perhaps the universe was created for the sole purpose of producing you and me. I have no objection to discussing the possibility, as long as the discussion is critical, rational, and objective. The most common argument that is still given by believers when they are asked to present scientific evidence for a creator is: "How can all of this (gesturing to the world around us) have happened by chance?" As we have seen, the most brilliant exposition of the case for evolution will not answer this question, because it still presumes the pre-existence of laws of physics and values of physical constants that had to be delicately balanced for human (and cockroach) life to evolve.


The Argument from Probability

Before addressing the question of how the laws of physics can have come about in the absence of intelligent design, let me provide a response to the arguments from probability outlined above.

If we properly compute, according to statistical theory, the probability for the universe existing with the properties it has, the result is unity! The universe exists with one hundred percent probability (unless you are an idealist who believes everything exists only in your own mind). On the other hand, the probability for one of a random set of universes being our particular universe is a different question. And the probability that one of a random set of universes is a universe that supports some form of life is a third question. I submit it is this last question that is the important one and that we have no reason to be sure that this probability is small.

I have made some estimates of the probability that a chance distribution of physical constants can produce a universe with properties sufficient that some form of life would have likely had sufficient time to evolve. In this study, I randomly varied the constants of physics (I assume the same laws of physics as exist in our universe, since I know no other) over a range of ten orders of magnitude around their existing values. For each resulting "toy" universe, I computed various quantities such as the size of atoms and the lifetimes of stars. I found that almost all combinations of physical constants lead to universes, albeit strange ones, that would live long enough for some type of complexity to form (Stenger 1995: chapter 8). This is illustrated in figure 1.



Figure 1. Distribution of stellar lifetimes for 100 random universes in which four basic physics constants (the proton and electron masses and the strengths of the electromagnetic and strong forces) are varied by ten orders of magnitude around their existing values in our universe. Otherwise, the laws of physics are unchanged. Note that in well over half the universes, stars live at least a billion years. From Stenger 1995.

Every shuffle of a deck of cards leads to a 52-card sequence that has low a priori probability, but has unit probability once the cards are all on the table. Similarly, the "fine-tuning" of the constants of physics, said to be so unlikely, could very well have been random; we just happen to be in the universe that turned up in that particular deal of the cards.

Note that my thesis does not require more than one universe to exist, although some cosmological theories propose this. Even if ours is the only universe, and that universe happened by chance, we have no basis to conclude that a universe without some form of life was so unlikely as to have required a miracle.


Simplicity and Physical Law

So the argument from probability fails. Many sets of physical constants could have produced a universe with life, albeit life very unlike our own. But what about the laws of physics themselves? Can we take their mere existence as evidence for intelligent design?

Let me begin by addressing two commonsense notions: (1) you cannot get something from nothing, and (2) the order of the universe requires the pre-existence of an active intelligence to do the ordering. I will leave it to the theologians to explain how the postulate of a creator God solves the problem of creation ex nihilo, since God is something that, itself, must have come, uncreated, from nothing. Instead I will address the physics issues implied by the creation of the universe from nothing. In physics terms, creation ex nihilo appears to violate both the first and second laws of thermodynamics.

The first law of thermodynamics is equivalent to the principle of conservation of energy: the total energy of a closed system is constant; any energy change must be compensated by a corresponding inflow or outflow from the system.

Einstein showed that mass and energy are equivalent, by E=mc2. So, if the universe started from "nothing," energy conservation would seem to have been violated by the creation of matter. Some energy from outside is apparently required.

However, our best estimate today is that the total energy of the universe is zero (within a small zero point energy that results from quantum fluctuations), with the positive energy of matter balanced by the negative potential energy of gravity. Since the total energy is zero, no energy was needed to produce the universe and the first law was not violated.

The second law of thermodynamics requires that the entropy, or disorder, of the universe must increase or at least stay constant with time. This would seem to imply that the universe started out in a greater state of order than it has today, and so must have been designed.

However, this argument holds only for a universe of constant volume. The maximum entropy of any object is that of a black hole of the same volume. In an expanding universe, the maximum allowable entropy of the universe is continually increasing, allowing more and more room for order to form as time goes by. If we extrapolate the big bang back to the earliest definable time, the so-called Planck time (10-43 second), we find that universe started out in a condition of maximum entropy -- total chaos. The universe had no order at the earliest definable instant. If there was a creator, it had nothing to create.

Note also that one cannot ask, much less answer, "What happened before the big bang?" Since no time earlier than the Planck time can be logically defined, the whole notion of time before the big bang is meaningless.

Furthermore, within the framework of Einstein's relativity, time is the fourth dimension of spacetime. Defining this fourth dimension as ict, where t is what you read on a clock, i = sqrt(-1), and c is the speed of light, the coordinates of time and space are interchangeable. In short, time is inextricably intertwined with space and came into being "when" or "where" (language is inadequate to mathematics here) spacetime came into being.


Spontaneous Order

So, where did the order of the universe come from, if it did not exist at the "beginning"? Where did the laws of physics come from, if not from some great lawgiver? We are now beginning to grasp how the laws of physics could have come about naturally, as the universe spontaneously exploded in the big bang.

To understand this, we first have to recognize the prejudice that is built into the whole concept of physical law. When Newton developed mechanics and gravity, the Judeo-Christian notion of God-given law was already deeply engraved in his thinking, by his culture. Even today, science is interpreted by public, media, and scientists alike as the process of learning the "mind of God."[1]

However, the laws of physics, at least in their formal expressions, are no less human inventions than the laws by which we govern ourselves. They represent our imperfect attempts at economical and useful descriptions of the observations we make with our senses and instruments. This is not to say we subjectively determine how the universe behaves, or that it has no orderly behavior. Few scientists deny that an objective, ordered reality exists that is independent of human life and experience. We simply have to recognize that the concept of "natural law" carries with it certain metaphysical baggage that is tied to our traditional, pre-scientific modes of thought. We are going a step beyond logic to conclude that the existence in the universe of order, which we conventionally label as the laws of nature, implies a cosmic lawgiver.

We are gradually learning that several of the laws of physics, those that seem the most universal and profound, are in fact little more than statements about the simplicity of nature that can almost go unsaid. The "laws" of energy, momentum, and angular momentum conservation have been shown to be statements about the homogeneity of space and time. The first law of thermodynamics, conservation of energy, results from there being no unique moment in time.[2] Conservation of momentum follows from the Copernican principle that there is no preferred position in space. Other conservation laws, such as charge and nucleon number, also arise from analogous assumptions of simplicity.

For the mathematically inclined, the conserved quantities are generators of the symmetry transformations involved. A homogeneous universe, one with a high level of symmetry, is the simplest of all possible universes, just the kind we would expect to happen by accident. In such a universe, many conservation laws will automatically exist.

In general, the conservation laws need no explanation beyond the mathematical symbols used to represent the corresponding symmetry. On the other hand, an observed violation of a conservation law would demand an explanation, for then we would have evidence for a deviation from simplicity and homogeneity. To explain this deviation, we have to go beyond the assumptions that require the fewest parameters, that is, are the most economical.

By an equally simple but somewhat different argument, the second law of thermodynamics is found not to be some underlying principle of the universe, but rather an arbitrary convention we humans make in defining the direction of time. Nothing in known fundamental physics forbids the violation of the second law. No mechanical principle prevents the air emptying from a room when you open the door, killing everyone inside. Physics does not forbid a human from growing younger or the dead rising! All that has to happen for these "miraculous" events is that the molecules involved are accidentally moving in the right direction at the right instant. Of course these miracles are not observed to happen except in fantasies, but only because they are so highly unlikely.

We introduce the second "law" to codify what all of human experience testifies, that air does not empty from a room, people do not grow younger, and the dead do not rise. But these events are not impossible, just highly improbable. Influenced, like Newton, by our culture, we falsely state that these unlikely events cannot happen because the second law "forbids" them from doing so.

The second law of thermodynamics, along with the arrow of time and the notions of causality and determinism, arise as statistical statements about the likelihood of events that emerge as principles we invent to describe the world of everyday experiences.

Other, more complex and less universal laws of physics appear to arise from spontaneously broken symmetries. When a quantity such as momentum is observed not to be conserved, we introduce the notion of a "force" to break the corresponding spatial symmetry. By this means, the force laws and other principles that give structure to the universe arise as spontaneously broken symmetries--accidental, uncaused events that occurred in the first fraction of a second of the big bang as the expanding universe cooled. The process can be likened to the formation of structure in a snowflake from water vapor, or the magnetizing of a bar of iron cooled below the Curie temperature.


The Appearance of Structure

While the details of the symmetry-breaking mechanism referred to here are not fully developed, and further work may negate this picture, we have at least one highly successful example of how the process of spontaneous structure formation from underlying symmetry and chaos can have come about. The current theory of elementary particles, the so-called Standard Model of quarks and leptons (the electron and neutrino are examples of leptons), agrees with all existing observations about the material world. In two decades since its inception, no violation of the Standard Model has been observed.

Within the framework of this model, electromagnetic and weak nuclear forces are viewed as low-energy manifestations of a single, unified electroweak force that applies at higher energies and smaller distances. At the level of most observations, these forces are vastly different. The electromagnetic force acts over macroscopic distances, while the electroweak force is confined to the atomic nucleus. The two forces differ enormously in strength. Yet the Standard Model treats them in a unified fashion at high energies, and explains their differing structure by means of spontaneous symmetry breaking that occurs at lower energies.

Further progress in understanding these fundamental mechanisms has been slowed by the canceling of the Superconducting Supercollider that would have probed beyond the Standard Model. A less ambitious (although still gigantic) project is going ahead in Europe, but it will be a new millennium before physicists have the data they will need to determine whether spontaneous symmetry breaking is indeed the process by which the laws of physics evolved in the first fraction of a second of the big bang. Currently, all we can say is that we have one firm example, and many theoretical suggestions, that will not be tested experimentally for another decade. Even if they all fail these tests, it seems highly unlikely that the process will yield evidence for the creator of Judeo-Christian-Islamic theology.


Implications for Education

In critically examining evidence for or against intelligent design to the universe, it must be understood that we are following the traditional practice of science, seeking a scientific explanation for observations about the universe that have been previously attributed to the action of supernatural deity. Believers will call us nasty names, like "atheist" and "secular humanist," and accuse us of undermining faith and morality.

Certainly we cannot be dogmatic in our approach, or appear to be preaching a religion of "scientism." If we do, then we have no more right to a piece of the science curriculum than the religionists.

As in any scientific investigation, we must emphasize our commitment to the scientific process and agree to accept whatever the conclusion of that process may be. If that conclusion is evidence for supernatural intelligent design, then so be it. But if we cannot find such evidence, then we should not feel compelled to soothe the sensitivities of believers by leaving unchallenged the assertion that their sectarian prejudices have scientific merit. We must speak out forcefully whenever anyone claims scientific authority for beliefs that fail the objective tests of scientific method.

I realize that the ideas I have covered in this essay will be very difficult to explain in the classroom, even at the university level where few students study physics at anything more than a minimal, descriptive level--if they study it at all. Nevertheless, we should not leave the field open to those who demonstrate no commitment to scientific truth.

If teachers cannot understand or explain the developments in modern physics I have outlined above, they can at least emphasize the need to pursue these issues in an open, objective, and rational fashion. They should point out the logical flaws in the anthropic probability argument, that we must count all the possible ways that life may have developed. And they can question the claim that creation ex nihilo violates the laws of physics, that science requires a miracle to produce the universe.

At the least, teachers should be made aware of the fact that modern physics and cosmology provide no compulsion to introduce the uneconomical hypothesis of a biblical creator. They must resist those who would attempt to force their personal beliefs into the classroom through the back door of "intelligent design."

The process in which we are engaged is the search for rational evidence for or against intelligent design. It does not suffice to say that intelligent design is possible, and proponents of intelligent design have no right to re-cast the question as one in which the non-existence of intelligent design must be proven. Within the framework of Occam's razor, intelligent design is an added hypothesis and the proponent's burden is to demonstrate why it is necessary to make this hypothesis. I have argued that no evidence or rational argument for intelligent design can be found in either the data or the theories of modern physics and cosmology. If the hypothesis of intelligent design is to be discussed in science classrooms, then good science methodology demands that we make clear that this is an uneconomical hypothesis that is not required by existing scientific knowledge.


The author is grateful to Taner Edis and John Forester for their comments on this essay.

Victor J. Stenger is professor of physics and astronomy at the University of Hawaii and the author of Not By Design: The Origin of the Universe (Prometheus Books, 1988) and Physics and Psychics: The Search for a World Beyond the Senses (Prometheus Books, 1990). This article is based on a chapter from his latest book: The Unconscious Quantum: Metaphysics in Modern Physics and Cosmology (Prometheus Books, 1995).


References

Barrow, John D. and Frank J. Tipler 1986.

Begley, Sharon 1994. "Science and the Sacred" Newsweek November 28: 56.

Cole, John 1995. NCSE Reports 15, 1:2

Davies, Paul 1992. The Mind of God: The Scientific Basis for a Rational World. New York: Simon and Schuster.

Davis, Percival and Dean H. Keaton 1993. Of Pandas and People. Haughton.

Hawking, Stephen 1988. A Brief History of Time: From the Big Bang to Black Holes. New York: Bantam.

Hoyle, F. and C. Wickramasinghe 1981. Evolution from Space. J. M. Dent.

Matsumura, Molleen 1995. NCSE Reports 15, 1: 7.

Penrose, Roger 1989. The Emperor's New Mind: Concerning Computers, Minds, and the Laws of Physics. Oxford: Oxford University Press.

Rolston III, Holmes 1986. "Shaken Atheism: A Look at the Fine-Tuned Universe." The Christian Century, December 3.

Stenger, Victor J. 1995. The Unconscious Quantum: Metaphysics in Modern Physics and Cosmology. Amherst, N. Y.: Prometheus Books.

Wright, Robert 1992. "What Does Science Tell Us About God?" Time December 28: 38.


Notes

[1] The "mind of God" were the final words of Stephen Hawking's remarkable best-seller, A Brief History of Time (Hawking, 1988). This catchy phrase was absconded by Paul Davies for the title his book, The Mind of God: The Scientific Basis for a Rational World (Davies, 1992). Physicist Davies has won a million dollar prize for his writings on religion and science.

[2] Admittedly, the first moment of the universe was unique, but the implied violation of conservation of energy is exactly what gives us the zero point energy mentioned earlier in the text.
http://www.talkorigins.org/faqs/cosmo.html


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Oud 07-02-2002, 17:13
legatus
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It is important to note that Darwin's book "The Origin of Species by Means of Natural Selection" did two things. It summarized all of the evidence in favor of the idea that all organisms have descended with modification from a common ancestor, and thus built a strong case for evolution. In addition Darwin advocated natural selection as a mechanism of evolution. Biologists no longer question whether evolution has occurred or is occurring. That part of Darwin's book is now considered to be so overwhelmingly demonstrated that is is often referred to as the FACT of evolution. However, the MECHANISM of evolution is still debated.

Van die zelfde site
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Oud 07-02-2002, 17:16
Demon of Fire
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legatus schreef:
It is important to note that Darwin's book "The Origin of Species by Means of Natural Selection" did two things. It summarized all of the evidence in favor of the idea that all organisms have descended with modification from a common ancestor, and thus built a strong case for evolution. In addition Darwin advocated natural selection as a mechanism of evolution. Biologists no longer question whether evolution has occurred or is occurring. That part of Darwin's book is now considered to be so overwhelmingly demonstrated that is is often referred to as the FACT of evolution. However, the MECHANISM of evolution is still debated.

Van die zelfde site

Precies, wij zijn bereid sceptisch te staan tegenover onze bevindingen. Maar dat de evolutie heeft plaatsgevonden, dat is zeker waar. Daar zijn zoals daar staat ook al genoeg bewijzen voor.

Maar hoe precies, daar zijn verschillende objectieve en wetenschappelijke theorieen over. Geen creationistische onzin.

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Oud 07-02-2002, 17:21
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Molecular biologist Michael Behe recently noted in his book, "Darwin's Black Box", that there are a host of biochemical systems which function much like machines. These machines work only if all the necessary parts are present for if one part is removed, the entire machine breaks down. These systems defy an evolutionary origin, because they cannot be built up in a step-by-step manner. Examples Behe gives include the bacterial flagellum, the blood clotting mechanism, and the biochemical processes behind vision. Reverse-engineering of these and other biological structures shows that evolutionary processes weren't at work in creating them.
William Dembski, in "The Design Inference" and "No Free Lunch" shows that Darwinian processes cannot explain much of biological complexity. Biological organisms--both at the macro and micro level--exhibit this sort of "irreducible complexity" and "specified, complex information. These properties of biological systems cannot be explained by evolution
http://www.talkorigins.org/faqs/behe.html


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Oud 07-02-2002, 17:40
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Evolutietheorie heeft ook z'n sterke punt en dat dingen evolueren is ook niet wat Intelligent Design/Creationisme ontkent. Het mechanisme van het ontstaan... daar ligt het.

science has by no means confirmed the traditional belief in a created universe with humanity at its center.

Dat zegt Intelligent Design ook niet.

[Dit bericht is aangepast door legatus (07-02-2002).]
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Oud 07-02-2002, 17:43
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legatus schreef:
Evolutietheorie heeft ook z'n sterke punt en dat dingen evolueren is ook niet wat Intelligent Design/Creationisme ontkent. Het mechanisme van het ontstaan... daar ligt het.

Creationisten zijn geen wetenschappers.

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Scientific creationism differs from conventional science in numerous and substantial ways. One obvious difference is the way scientists and creationists deal with error.

Science is wedded, at least in principle, to the evidence. Creationism is unabashedly wedded to doctrine, as evidenced by the statements of belief required by various creationist organizations and the professions of faith made by individual creationists. Because creationism is first and foremost a matter of Biblical faith, evidence from the natural world can only be of secondary importance. Authoritarian systems like creationism tend to instill in their adherents a peculiar view of truth.

Many prominent creationists apparently have the same view of truth as political radicals: whatever advances the cause is true, whatever damages the cause is false. From this viewpoint, errors should be covered up where possible and only acknowledged when failure to do so threatens greater damage to the cause. If colleagues spread errors, it is better not to criticize them publicly. Better to have followers deceived than to have them question the legitimacy of their leaders. In science, fame accrues to those who overturn errors. In dogmatic systems, one who unnecessarily exposes an error to the public is a traitor or an apostate.

Ironically, creationists make much of scientific errors. The "Nebraska Man" fiasco, where the tooth of an extinct peccary was misidentified as belonging to a primitive human, is ubiquitous in creationist literature and debate presentations. So is the "Piltdown Man" hoax. Indeed, creationist propagandists often present these two scientific errors as characteristic of paleoanthropology. It is significant that these errors were uncovered and corrected from within the scientific community. In contrast, creationists rarely expose their own errors, and they sometimes fail to correct them when others expose them.

Duane Gish, a protein biochemist with a Ph.D. from Berkeley, is vice president of the Institute for Creation Research (ICR) and creationism's best-known spokesman. A veteran of perhaps 150 public debates and thousands of lectures and sermons on creationism, Gish is revered among creationists as a great scientist and a tireless fighter for the truth. Among noncreationists, however, Gish has a reputation for making erroneous statements and then pugnaciously refusing to acknowledge them. One example is an unfinished epic which might be called the tale of two proteins.

In July 1983, the Public Broadcasting System televised an hour-long program on creationism. One of the scientists interviewed, biochemist Russell Doolittle, discussed the similarities of human proteins to chimpanzee proteins. In many cases, corresponding human and chimpanzee proteins are identical, and in others they differ by only a few amino acids. This strongly suggests a common ancestry for humans and apes. Gish was asked to comment. He replied:


If we look at certain proteins, yes, man then -- it can be assumed that man is more closely related to a chimpanzee than other things. But on the other hand, if you look at other certain proteins, you'll find that man is more closely related to a bullfrog than he is a chimpanzee. If you focus your attention on other proteins, you'll find that man is more closely related to a chicken than he is to a chimpanzee.
I had never heard of such proteins, so I asked a few biochemists. They hadn't, either. I wrote to Gish for supporting documentation. He ignored my first letter. In reply to my second, he referred me to Berkeley geochronologist Garniss Curtis. I wrote to Curtis, who replied immediately.

Some years ago, Curtis attended a conference in Austria where he heard that someone had found bullfrog blood proteins very similar to human blood proteins. Curtis offered an explanatory hypothesis: the "frog" which yielded the proteins was (he suggested) an enchanted prince. He then predicted that the research would never be confirmed. He was apparently correct, for nothing has been heard of the proteins since. But Duane Gish once heard Curtis tell his little story.

This bullfrog "documentation" (as Gish now calls it) struck me as joke, even by creationist standards, and Gish simply ignored his alleged chicken proteins. In contrast, Doolittle backed his televised claims with published protein sequence data. I wrote to Gish again suggesting that he should be able to do the same. He didn't reply. Indeed, he has never since replied to any of my letters.

John W. Patterson and I attended the 1983 National Creation Conference in Roseville, Minnesota. We had several conversations there with Kevin Wirth, Research Director of Students for Origins Research (SOR). At some point, we told him the protein story and suggested that Gish might have lied on national television. Wirth was confident that Gish could document his claims. He told us that if we put our charges in the form of a letter, he would do his best to get it published in Origins Research, the SOR tabloid.

Gish also attended the conference, and I asked him about the proteins in the presence of several creationists. Gish tried mightily to evade and/or obfuscate, but I was firm. Doolittle provided sequence data for human and chimpanzee proteins; Gish could do the same -- if his alleged chicken and bullfrog proteins really exist. Gish insisted they exist and promised to send me the sequences. Skeptical, I asked him pointblank: "Will that be before hell freezes over?" He assured me that it would. After 2-1/2 years, I still have neither sequence data nor a report of frost in Hades.

Shortly after the conference, Patterson and I submitted a joint letter to Origins Research, briefly recounting the protein story and concluding, "We think Gish lied on national television." We sent Gish a copy of the letter in the same mail. During the next few months, Wirth (and probably others at SOR) practically begged Gish to submit a reply for publication. In response, someone at ICR (presumably Gish himself) pressured SOR not to publish our letter.(1) Unlike Gish, however, Kevin Wirth was as good as his word. The letter appeared in the Spring 1984 issue of Origins Research -- with no reply from Gish.

The 1984 National Bible-Science Conference was held in Cleveland, and again Patterson and I attended. Again, I asked Gish for sequence data for his chicken and bullfrog proteins. This time, Gish told me that any further documentation for his proteins is up to Garniss Curtis and me.

I next saw Gish at noon on February 18, 1985, when he debated philosopher of science Philip Kitcher at the University of Minnesota. Several days earlier, I had heralded Gish's coming (and his mythical proteins) in a guest editorial in the student newspaper.(2) Kitcher alluded to the proteins early in the debate, and in his final remarks, he demanded that Gish either produce references or admit that they do not exist. Gish, of course, did neither. His closing remarks were punctuated with sporadic cries of "Bullfrog!" from the audience.

That evening, Duane Gish addressed about 200 people assembled in a hall at the student union. During the question period, Stan Weinberg, a founder of the Committees of Correspondence on Evolution, stood up. Scientists sometimes make mistakes, said Weinberg, and when they do, they own up to them. Had Gish ever made a mistake in his writings and presentations? If so, could his chicken and bullfrog proteins have been a mistake? Gish made a remarkable reply.

He has indeed made mistakes, he said. For instance, an erroneous translation by another creationist (Kofahl) once led him to believe that hydrogen peroxide and hydroquinone, two chemicals used by the bombardier beetle, spontaneously explode when mixed. This error led him to claim in a book and in his presentations that the beetle had to evolve a chemical inhibitor to keep from blowing itself up. When he learned that hydrogen peroxide and hydroquinone do not explode when mixed, he said, he corrected the error in his book.

Regarding the bullfrog proteins, Gish said he relied on Garniss Curtis for them. Perhaps Curtis was wrong. As for the chicken proteins, Gish made a convoluted and (to a nonbiochemist) confusing argument about chicken lysozyme. It was essentially the same answer he had given me immediately after his debate with Kitcher, when I went onstage and asked him once again for references. It was the same answer he would give two nights later in Ames, Iowa, in response to a challenge by John W. Patterson. I will discuss its substance, relevance, and potential for deception after dealing with the bombardier beetle.

Gish neglected to mention certain details of the bombardier beetle business. Early in 1978, Bill Thwaites and Frank Awbrey of San Diego State University mixed hydrogen peroxide and hydroquinone in front of their "two model" class with a nonexplosive result.(3) Gish may have corrected his book, but he continued to use demonstrably false arguments about the bombardier beetle in debate presentations. I personally heard him do so on January 17, 1980, in a debate with John W. Patterson at Graceland College in Lamoni, Iowa.

About the chicken lysozyme: Three times in three days, Gish was challenged to produce references for chicken proteins closer to human proteins than the corresponding chimpanzee proteins. Three times, he responded with his chicken lysozyme apologetic. Few of his creationist listeners know what lysozyme is, and perhaps none of them knew that human and chimpanzee lysozyme are identical, and chicken lysozyme differs from both by 51 out of 130 amino acids.(4) To one unfamiliar with biochemistry and (especially) Gish's apologetic methods, it sounded like he responded to the question. Whether by design or by some random process, Gish's chicken lysozyme apologetic was admirably suited to deceive listeners.

One who was taken in by it was Crockett Grabbe, a physicist with the University of Iowa. As a result, Grabbe wrongly accused Gish of claiming chicken lysozyme is closer to human lysozyme than is chimpanzee lysozyme. Gish then counterattacked, playing "blame the victim" and pretending it was Grabbe's own fault that he was deceived.(5) But if the chicken lysozyme apologetic fooled a professional scientist, it's unlikely that many of the creationist listeners saw through it.

Gish's refusal to acknowledge the nonexistence of his chicken protein is characteristic of ICR. His boss, Henry Morris, gave Gish's handling of the matter his tacit approval by what he said (and didn't say) about it in his History of Modern Creationism. Morris referred to the protein incident and took a swipe at Russell Doolittle (who he identified as "Richard Doolittle"), but he offered no criticism of Gish's conduct. Instead, he accused PBS of misrepresenting Gish!(6)

Meanwhile, Gish has been obfuscating behind the scenes. The only creationist publication to directly address the protein affair has been Origins Research. In the Fall 1985 issue, editor Dennis Wagner (1) wrongly identified Glyn Isaac as the source of Gish's bullfrog and (2) wrongly stated that Gish sent me a tape of the lecture in which Isaac supposedly made the statement. Wagner's source, it turns out, is a letter Gish wrote to Kevin Wirth,(7) in which Gish apparently confused Glyn Isaac with Garniss Curtis. He also claimed to have a tape and a transcript of the "Isaac" (presumably Curtis) lecture, and he claimed that he had reviewed them. In the same sentence, Gish claimed that he sent me his "documentation," and Wagner quite naturally assumed that meant at least the tape. But Gish sent me neither, nor has he sent copies of said tape or transcript to others requesting them. As with his chicken proteins, we have only Gish's word for their existence.

For the record, it is no longer important whether Gish's original statements about chicken and bullfrog proteins were deceptions or incredible blunders. It is now going on four years since the PBS broadcast, and Gish has neither retracted his chicken statement nor attempted to justify it. (Obviously, the lysozyme apologetic doesn't count, but it took Gish 2-1/2 years to come up with that!) And if the Curtis story is all he knows about his chimpanzee protein, on what basis did he promise to send me its sequence at the 1983 National Bible-Science Conference? Gish has woven himself into an incredible web of contradictions, and even some creationists now suspect that he has been less than candid.

Gish's steadfast refusal to acknowledge the facts seems to characterize creationism. Consider the case of the alleged Paluxy River "manprints." These have played an important role in creationist apologetics since Whitcomb and Morris published photographs of "manprint" carvings owned by Clifford Burdick in the Genesis Flood in 1961. The film "Footprints in Stone" features several trackways presented as human footprints in Cretaceous limestone. ICR has long featured them in its museum, and John D. Morris, son of ICR founder Henry Morris, wrote a popular book about them. But creationism's Paluxy River apologetics are rapidly collapsing.

Glen Kuban has been investigating the Paluxy River tracks since 1980. In 1982, Kuban noted that the prints of the principal trail in "Footprints in Stone" (called the "Taylor trail" after Reverend Stan Taylor, producer of the film) have gradually turned a reddish color. The colored areas represent the material which filled the original prints. Extending beyond the visible depressions, the markings clearly delineate three-toed dinosaur prints. The three other "manprint" trails on the site exhibit the same phenomenon.

Stan Taylor is deceased, but his son Paul now runs Films for Christ. Last fall, Kuban persuaded Paul Taylor to revisit the site and see the evidence for himself. Taylor was so impressed that he withdrew "Footprints in Stone" from circulation. He also repudiated the "mantracks" in a two-page statement which was supposed to be sent to those requesting the film. These actions, almost unprecedented in the annals of creationism, would be more noteworthy except for three things: (1) a second, slightly watered-down statement quickly replaced the initial statement, (2) Taylor has not granted permission to publish the document, and (3) several persons who have since requested the film have not received the statement but instead have been told that the film is not available for the requested date.(8)

As for ICR, Kuban also convinced John D. Morris to revisit the site. After "Footprints in Stone," Morris's 1980 book Tracking Those Incredible Dinosaurs and the People Who Knew Them is the most important piece of "manprint" propaganda. He responded to the new evidence in a January 1986 Impact article, "The Paluxy River Mystery." It is vintage creationism.

In the article, Morris obscures the fact that all of the crucial research was done by Kuban and other noncreationists. He backhands knowledgeable critics like John Cole, Steven Schafersman, Laurie Godfrey, and Ronnie Hastings (collectively, "Raiders of the Lost Tracks"), accusing them of "ignoring, ridiculing and distorting the evidence as reported by creationists." Near the end, Kuban is mentioned in passing as the first to notice the coloration changes, but no reader could guess that it took several years for Kuban to convince Morris to come look at the new evidence. Through Kuban's charity, Morris was able to preempt publication of Kuban's original research, and he showed his gratitude by barely mentioning Kuban's name!

Nor is that all. In his windup, Morris muddies the Paluxy waters with a vague hint that the colorations might be fraudulent. While he concludes that "it would now be improper for creationists to continue to use the Paluxy data as evidence against evolution," he says nothing whatever about withdrawing his thoroughly-discredited book from the market.

In the March 1986 Acts & Facts, an unnamed author (presumably Henry Morris) defends John Morris's half-hearted retraction in an unapologetic apologetic. Regarding John Morris's hints about fraudulent colorations, the anonymous author of "Following Up on the Paluxy Mystery" notes that "no evidence of fraud has been found, and some hints of these dinosaur toe stains have now possibly been discerned on photos taken when the prints in question were originally discovered." Glen Kuban, who pointed out these stains in the early photos,(9) is not mentioned at all. Indeed, the original creationist interpretation of the trackways is characterized as "not only a valid interpretation but arguably the best interpretation of the data available at that time." The "closed-minded" evolutionists who have criticized the Paluxy tracks are mentioned only with sneer and smear.

Another creationist organization with a heavy stake in the Paluxy River footprints is the Bible-Science Association. Reverend Paul Bartz, editor of the Bible-Science Newsletter, has hotly defended "Footprints in Stone" and editorially sneered at the work of the "Raiders." After Films for Christ withdrew "Footprints in Stone," I watched the Bible-Science Newsletter for a reaction. Nothing. BSA headquarters are in Minneapolis, and BSA officials are active in the Twin Cities Creation-Science Association. I attended TCCSA meetings to hear what BSA had to say in that forum. Nothing. I privately showed BSA Field Director Bill Overn an unpublished manuscript on the tracks. About a month later, BSA finally broke its silence.

The March 1986 Bible-Science Newsletter carried a column entitled "BSA Issues Statement on the Paluxy Footprints." The statement, which is in the form of a press release, ignores Kuban altogether, referring only to John Morris's Impact article. It quotes a statement by Morris affirming his commitment to truth and facts, commenting:


Our stance is identical. Our readership is different, however, and expects us to present a more studied and mature documented position. The Bible-Science Association is currently engaged in an evaluation of current data as well as the exploration of additional data which has not yet been fully examined.
Any serious study of the matter, of course, would have to begin with Glen Kuban, whose research blew the lid off "Footprints in Stone." Shortly after that issue of the Bible-Science Newsletter came out, I called Kuban and asked if he had been contacted by BSA. He hadn't. It's not clear how a "more mature documented position" on the tracks can be presented without contacting the man most knowledgeable about them. But perhaps the BSA writer gives a hint of things to come with the next sentence:


We also point out to our readers that current questions concerning the value of the Paluxy findings do not revolve around the question of whether any kind of evidence ever existed to support the contention of contemporaneous human and dinosaur existence in the Paluxy river bed (italics original).
I might similarly point out to my readers that current questions concerning the value of perpetual motion machines do not revolve around the question of whether any kind of evidence ever existed for machines which could create energy from nothing. I prefer to point out that such an argument is bankrupt, and therefore, precisely the kind of apologetic to which perpetual motionists and creationists must resort.

The BSA statement also neglected to mention three important claims BSA itself has made about alleged Paluxy River mantracks:


1. BSA, which has been lavish in its praise for "Footprints in Stone," failed to inform its readers that Films for Christ has withdrawn it from circulation because it misidentifies dinosaur tracks as human.
2. BSA has been the foremost promoter of the Reverend Carl Baugh and his alleged human footprints. Knowledgeable creationists now recognize that Baugh's "manprints" are as questionable as his scientific degrees. Two BSA insiders told me privately that they have had their doubts about Baugh for some time, and they no longer actively promote him in the Bible-Science Newsletter. No hint of Baugh's fall from grace has reached subscribers.

3. BSA has long promoted as genuine an alleged giant human print known as "the Caldwell Print," and they even sell aluminum casts of it. Besides its anatomical absurdities, knowledgable creationists have recently alleged that it is a carving. The BSA statement says nothing whatever about this, nor has BSA announced that the print is no longer for sale.

For now, at least, it is whitewash as usual from the Bible-Science Association. If the past is prologue, the Bible-Science Newsletter will eventually acknowledge the action by Films for Christ, and they might quietly quit distributing the Caldwell Print (if they haven't already). But they will never blow the whistle on Reverend Carl Baugh's misrepresented discoveries, mythical degrees, and general scientific incompetence.

With these examples in mind, it is hardly surprising that ICR continues to promote errors refuted more than a decade ago. Those who take the time to reply to creationist attacks on science find themselves slaying the slain a thousand times over. And no matter how dead a creationist error might appear to be, it always has the hope of resurrection in the Bible-Science Newsletter.

Creationism is not monolithic. Nevertheless, creationism as a movement is and ever will be judged by the most visible organizations and individuals. On that basis, the public can only conclude that the typical creationist response to error is silence, whitewash, or outright denial. If some creationists are offended by this interpretation (and several have told me privately that they are), I refuse to be their spokesman. If they cannot denounce these actions on their own, their silence makes them participants.

NOTES

1. Kevin Wirth, personal communication.

2. Schadewald, Robert J. "The Gospel of Creation: The Book of Misinformation," Minnesota Daily, v. 86, n. 112 (February 14, 1985), p. 7.

3. Weber, Christopher Gregory, "The Bombardier Beetle Myth Exploded," Creation/Evolution, n. 3 (Winter 1981).

4. Awbrey, Frank T. and William M. Thwaites, "A Closer Look at Some Biochemical Data that 'Support' Creation," Creation/Evolution, n. 7 (Winter 1982), p. 15.

5. Gish, Duane T., "Creationism Misassailed," Cedar Rapids Gazette, 8/14/85.

6. Morris, Henry M., History of Modern Creationism (San Diego, Master Book Publishers, 1984), p. 316.

7. Letter, Duane T. Gish to Kevin Wirth, 2/27/84.

8. Glen Kuban, personal communication.

9. Glen Kuban, personal communication.

Daarom komen ze ook bijna nooit in 'Nature' of de 'New scientist' te staan. De gevens die ze leveren kloppen toch niet. Of worden aangepast naar hun eigen inzicht. Kansberekening hebben ze blijkbaar een geheel eigen systeem voor, ze kennen geen wiskunde.

Groetjes
Ben(die ze daarom niet vertrouwd
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Oud 07-02-2002, 17:51
legatus
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If we extrapolate the big bang back to the earliest definable time, the so-called Planck time (10-43 second), we find that universe started out in a condition of maximum entropy -- total chaos. The universe had no order at the earliest definable instant. If there was a creator, it had nothing to create.

Spreken ze zichzelf dan niet tegen? Er was niks om te maken door een creator maar evolutie kon zichzelf wel maken uit dit niks?
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Oud 07-02-2002, 17:53
Demon of Fire
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legatus schreef:
If we extrapolate the big bang back to the earliest definable time, the so-called Planck time (10-43 second), we find that universe started out in a condition of maximum entropy -- total chaos. The universe had no order at the earliest definable instant. If there was a creator, it had nothing to create.

Spreken ze zichzelf dan niet tegen? Er was niks om te maken door een creator maar evolutie kon zichzelf wel maken uit dit niks?

The universe had no order at the earliest definable instant.

Nee!

De chaos was als gevolg van maximale entropy. Dat was in een extreem klein volume. In het allereerste begin...(planck tijd)

Waarna het heelal groter werd, had je ook geen maximale entropy meer en dus vormde er zich deeltjes en elementen etc.

Groetjes
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Oud 07-02-2002, 17:57
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The process in which we are engaged is the search for rational evidence for or against intelligent design. It does not suffice to say that intelligent design is possible, and proponents of intelligent design have no right to re-cast the question as one in which the non-existence of intelligent design must be proven. Within the framework of Occam's razor, intelligent design is an added hypothesis and the proponent's burden is to demonstrate why it is necessary to make this hypothesis. I have argued that no evidence or rational argument for intelligent design can be found in either the data or the theories of modern physics and cosmology. If the hypothesis of intelligent design is to be discussed in science classrooms, then good science methodology demands that we make clear that this is an uneconomical hypothesis that is not required by existing scientific knowledge.

Vreemd dat ze op Occam een beroep doen, hij had een stelling maar wou er iets anders mee bewijzen.
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Oud 07-02-2002, 18:01
Demon of Fire
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Vreemd dat ze op Occam een beroep doen, hij had een stelling maar wou er iets anders mee bewijzen.

Scrödinger had ook een leuke theorie waarmee hij iets geheel anders voor ogen had.
Hij heeft tot aan zijn dood niet geloofd in de quantummechnica. Toch is hij zeg maar de vader van deze theorie.

Dus hij mag dan zelf iets anders in gedachten hebben gehad, maar toch kun je er meer uit halen dan hij bedoelde of zelf heeft kunnen overzien.

Groetjes
Ben(die Ockham's scheermes een leuke stelling vind
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Oud 07-02-2002, 18:05
legatus
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Inderdaad een leuke stelling. Doe er ook wel eens stiekem beroep op.

Waarna het heelal groter werd, had je ook geen maximale entropy meer en dus vormde er zich deeltjes en elementen etc.

Dus nu groeit het heelal wel weer?

When general relativity says that 'space stretches', we are left with a whole gaggle of human intuition problems just like the one you posed in this question. Big Bang cosmology is based on General Relativity, and there are two kinds of universes described by it. Closed-finite universes and open-infinite ones. In the closed universe ( which ours seems not to be according to the data we have) 3-d space is finite in volume at every instant, and in the far future, the eventual collapse will decrease this volume to zero and then there will be no more 3-d space in existence. General relativity says that there is no 'external space' in which our universe exists, so human intuition fails miserably. Human intuition DEMANDS that there exist an external space for our universe to 'float' in like a soap bubble, which is the physical analogy your mind is using anyway to understand the universe. In an open-infinite universe, 3-d space has ALWAYS been infinite, even at the 'birth' of the universe at the Big Bang. This model is favored by Inflationary Cosmology, in which our universe is just one of an infinite number of 'patches' of 3-d space that exist in some larger arena. The expansion of out particular patch, however, does not happen at the expense of the compaction of the space surrounding it. Again, this is an intuitive paradox that humans cannot resolve because it seems contradictory...though mathematically it derives from a higher logic than we are commonly familiar with in our limited world.

[Dit bericht is aangepast door legatus (07-02-2002).]
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Oud 07-02-2002, 18:18
Demon of Fire
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Citaat:
legatus schreef:
Inderdaad een leuke stelling. Doe er ook wel eens stiekem beroep op.

Waarna het heelal groter werd, had je ook geen maximale entropy meer en dus vormde er zich deeltjes en elementen etc.

Dus nu groeit het heelal wel weer?

When general relativity says that 'space stretches', we are left with a whole gaggle of human intuition problems just like the one you posed in this question. Big Bang cosmology is based on General Relativity, and there are two kinds of universes described by it. Closed-finite universes and open-infinite ones. In the closed universe ( which ours seems not to be according to the data we have) 3-d space is finite in volume at every instant, and in the far future, the eventual collapse will decrease this volume to zero and then there will be no more 3-d space in existence. General relativity says that there is no 'external space' in which our universe exists, so human intuition fails miserably. Human intuition DEMANDS that there exist an external space for our universe to 'float' in like a soap bubble, which is the physical analogy your mind is using anyway to understand the universe. In an open-infinite universe, 3-d space has ALWAYS been infinite, even at the 'birth' of the universe at the Big Bang. This model is favored by Inflationary Cosmology, in which our universe is just one of an infinite number of 'patches' of 3-d space that exist in some larger arena. The expansion of out particular patch, however, does not happen at the expense of the compaction of the space surrounding it. Again, this is an intuitive paradox that humans cannot resolve because it seems contradictory...though mathematically it derives from a higher logic than we are commonly familiar with in our limited world.

[Dit bericht is aangepast door legatus (07-02-2002).]

Het heelal zet uit, tenminste dat is zoals we er nu voor staan.

Uit het doppler-effect blijkt dat sterren van ons af bewegen en sterker nog, ze versnellen.
Dus het lijkt er ook niet op dat er genoeg massa zou zijn in het heelal om een 'Big Crunch' te veroorzaken.

Iets wat van elkaar af beweegt, moet ook een begin hebben gehad. Dat duidt op een Oerknal. En daarnaast is er achtergrondstraling, in alle richtingen hetzelfde.

Het is inderdaad een erg complex fenomeen, maar ja, niemand heeft gezegd dat het leven of het helaal simpel is.
Waren/zijn maar weinig mensen die zoiets kunnen bevatten of van die ingewikkelde dingen kunnen bedenken.

Hoe je het ook went of keert. Al die ideeen zijn wel degelijk afkomstig van de menselijke geest en door mensen bedacht. Dus er zijn mensen die het kunnen bevatten. Einstein was er b.v. 1 van.

Groetjes
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Oud 08-02-2002, 19:34
legatus
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Uiteraard zie ik het niet zoals bepaalde volgers van het creationisme (wat achteraf inderdaad ID is.) dat een creator gelijk bij het begin aanwezig was en alles maakte. Maar dat er wellicht levensvormen eerder zijn ontwikkelt dan de mens en uitgestorven zijn die wellicht een vinger in de pap hebben gehad. Ik sluit niks uit. Evolutie is ook de theorie waar ik achtersta maar toch vind ik het niet onbedenkelijk dat er invloeden zijn geweest van een niet-aardse oorsprong.
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