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Ik heb hier vorig jaar een verslag over geschreven:
Citaat:
INTRODUCTION
Imagine this: It’s Friday night, you are in the pub with a couple of friends. You are watching a soccer game. But there is something else you are watching: a girl. In the twilight of the pub she looks very nice. She has a very attractive body, a cute face, large deep-blue eyes and long, dark-brown, curly hair. After you have plucked up some courage you give it a go and try to seduce her. Above all expectations you succeed and you start dating her. But after a while you find that she is not as slender as she first looked, her eyes looked large because of the make-up she used. In fact… her eyes are not even deep blue! She was wearing lenses when you first met her. And her hair: she just had it done at a very expensive barber’s… Fake curls and a fake colour.
As you can see from the above; it is not difficult to fool someone about your genes in our society. For every little beauty-flaw there is a cure, from make-up to extensive plastic surgery.
But not only for beauty-flaws there are cures. These days, many illnesses and ailments can be cured. In the last century medical science has made it possible for people who have a deadly disease like tuberculosis or small-pocks to be cured. A century ago this was not possible and only the fittest would have survived and have passed on their genes.
On top of that, we no longer adapt to natures needs but we adapt nature to our needs. Predators that might kill humans, like wolves are greatly diminished in numbers, or even extinct! Rivers that might flood and kill people are dammed. We have genetically altered plants that produce more food. And these are just a couple of examples.
When you look at the basic principle of evolution, ‘Survival of the fittest’, you start to wonder who is the fittest. Is this principle still at work in our society? Are we not all as fit as the latest medical science and the hottest line of make-up or clothing? Or are we? New epidemics to which we have no cure keep emerging, not everyone can afford expensive clothing or plastic surgery and of course our DNA still mutates. But will these things matter in our society? That is the question…
THE EVIDENCE FOR EVOLUTION
In order to make my point clear on the subject mentioned in the introduction, it is first necessary to discuss the evidence for evolution.
With his Theory of Evolution by means of Natural Selection, Darwin caused a shock in the established scientific world of his time. His theory implied that evolution is the logical result of four postulates. In essence they mean that if there are differences among individuals in a population that can be passed on to the next generation, and if there is differential success among those individuals in surviving, than some traits will be passed on more frequently than others. This implies that a population will change gradually over time.
Darwin based these postulates on a number of phenomena. First of all, he looked at living species. When you observe a population directly you can observe microevolution, small scale changes. But when we look at the bodies of living organisms, we might find evidence of large and extensive changes: macroevolution.
One piece of evidence for evolution is the direct observation of change through time. Many populations have been monitored by biologists for a long period. In some cases, like that of the soapberry bug, change has been observed. Changes can be caused by a sudden change in an environmental factor. In the case of the soapberry bug it was the coming of another kind of food.
Another piece of evidence for evolution is the presence of vestigial organs in some species. Vestigial organs or structures are functionless organs, remains of an organ that was once useful. We have some vestigial organ ourselves like our tailbone and the arrector pili muscle in our skin. It is not visible anymore and has no function whatsoever now but it is evidence we once had a tail. Other examples are the presence of eye sockets but no eyes in cave dwelling species and the remains of hips and legs with snakes and whales. But not only organs can be vestigial: it is also possible with genes. When this is the case, they are called pseudogenes. These pseudogenes are ‘false genes’. They are still present in DNA, but they do not code for anything anymore.
Other evidence comes from fossil records. One of them is very topical because of the greenhouse effect: extinction. The fact of extinction suggests that Earths flora and fauna have changed over time. These changes must have favoured some species and disfavoured other species and therefore some species became more abundant and other species became extinct.
The law of succession is more evidence that can be derived from fossil records. It means that close resemblances can be found between fossils and existing species.
Transitional forms are a third piece of evidence that can be derived from fossil records. Since evolution is a very gradual process, transitional forms will form. A good example of this is the Archaeopteryx, the flying dinosaur which still has major characteristics of a dinosaur (its skeleton) but also the ability to fly like modern birds.
The last major piece of evidence derived from fossil records is the evidence for environmental change. The fact that you can find marine fossils on high peaks in the Andes says a lot. Earth has undoubtedly changed in its 4.6 billion year long lifespan.
When you put several species in an evolutionary tree, or phylogeny, you can trace back a common ancestor. This common ancestor is also evidence for the evolution theory. It is possible to see which species branched from this tree before the other because of shared and not-shared mutations.
Common ancestry is also reflected by homology, likeness. There are two types of homology: structural, development and structural homology. Structural homology means that different species share the same type of bones, even though the function of these bones is radically different. Good examples of structural homology are the forelimbs of many vertebrates. The hoof of a horse, the wing of a bat, the hand of a human and the paw of a mole are very different in function but have the same basic build-up. Development homology means that the embryonic stage of many vertebrates is the same. Only in the late stage of development it becomes possible to see what the adult form of an animal will be like.
There are also nonhomologous similarities like that of a shark and an orca: they have the same shape but are in no way related, nor do they share the same bones. They are similar in shape because it is a very functional shape.
NATURAL SELECTION
Natural selection is the basis of Darwin’s Evolution Theory. In it four postulates are mentioned:
1. Individuals within a population are variable
2. The variations among individuals are, at least in part, passed from parents to offspring.
3. In every generation, some individuals are more successful at surviving and reproducing offspring than others.
4. The survival and reproduction of individuals are not random; instead they are tied to the variation among individuals. The individuals with the most favourable variations, those who are better at surviving and reproducing, are naturally selected.
Given these four postulates, the characteristics of a population will change slightly with each succeeding generation. These changes are the result of natural selection on a population. When one individual has more chance of surviving and producing offspring, it is more fit. By this way Darwin gave a whole new meaning to the word fit. Darwinian fitness is the ability of an individual to survive and reproduce in its environment. Fitness is relative; it refers to how well an individual is able to survive and reproduce compared to others. When an organism has a trait or characteristic that increases its fitness relative to other individuals without this trait, it is referred to as fitness.
When a certain trait grants an individual more fitness, this trait will be passed on to more offspring than usual. Therefore this trait will become more abundant and even more organisms will get this trait. Eventually all organisms in a population will have this trait. You can conclude from this that natural selection acts on individuals, but its consequences occur in populations.
In a population, the genetic variation can be quite large. But these variations or mutations have to be expressed in the phenotype to have any effect. A mutation in an intron is useless. When a variation in genotype is expressed in the phenotype and grants better fitness, it will be passed on to more offspring and eventually its allele frequency will become higher. Therefore natural selection acts on the phenotype, but evolution consists of changes in allele frequencies. This principle will become quite important further on in my case.
Of course, in order for selection to work, traits have to be present. But this doesn’t mean that new traits can’t evolve. This can happen in all species through mutations, and only in sexually reproducing species through meiosis and fertilization. During fertilization genes of genetically different parents are added to form new traits. Fertilization and mutation create new traits for selection to act upon.
Because natural selection increases adaptation, it is non-random. But increasing adaptation does not necessarily mean that it works towards a goal. It is not progressive, nor is it forward-looking, nor is it perfect.
MODERN MAN AND NATURAL SELECTION
When you apply the principles of evolution on the modern man there is a big problem: where is the natural selection? Our level of intelligence testifies of a big evolutionary success, but for several reasons it might also be our ‘downfall’. Natural selection acts on the phenotype, but evolution consists of changes in allele frequencies. We have become able to ‘change’ our phenotype and therefore evolution becomes much more complicated.
This changing of phenotypes becomes apparent in some ways: plastic surgery and other beauty products fool someone about your genes. Medical science allows not only the fittest but also the less fit to survive and pass on their genes. Another problem is that we adapt nature to our needs where it should be the other way around. But will nature allow this? Or will she strike back. In this paragraph I want to examine the effects of these developments more closely.
Medical science
Since the invention of vaccination and penicillin, medical science has come a long way. In medieval times there were many diseases to which man had no answer, for example Tuberculosis, the Plague and smallpox. In those times these diseases were seen as divine intervention, a punishment of God. But slowly man began to learn more about diseases and the way they work. This knowledge then was used to combat these illnesses.
In our modern society it is possible for people with a malfunctioning organ like a bad hart, to have a transplant and receive a new hart, people with diabetes can inject insulin and so on. These are very good things of course in the sense of the individual. But when you look at the whole species, this might not be such a beneficial development. When man would not have invented something like antibiotics against tuberculosis, only the fitter people would have survived this infection, and only the fitter people would have been able to pass on their genes. This is the basic principle of natural selection. But because we have become so intelligent that we can provide other means of protection, natural selection is no longer the only way of selection. In this way man has come to something of an evolutionary standstill. It is no longer a trait that one has that provide the advantage of some individuals over others, but it is the medical science. If you are ill, you no longer need to rely on your own body, medical science will help you. This way allele frequencies that would otherwise have declined, do not decline now and these less fit genes will be passed on.
Another good example of the effect of medical science on evolution is the breaking of a limb. If an animal breaks a leg, it does not have a large chance of surviving because it cannot gather food, run from predators and there is always the chance of an infection. If we break a leg, it is not even a big deal to let it heal perfectly. Food will be provided and we have no predators or infections to be afraid of.
Plastic surgery
Plastic surgery and beauty products are also a problem for evolution. It is known that our genotype is expressed in our phenotype. So not only the favourable genes, but also the less favourable are visible. When an organism selects a partner, it selects by appearance, behaviour, smell, in essence: its phenotype, in which its genotype is expressed. This is sexual selection. The purpose of sexual selection is to produce the best and fittest offspring.
Humans have long been using products like make-up. It is known that even the Egyptians used it. But it is the rise of plastic surgery that is the biggest problem for evolution. If a woman is 50 but she wants to look like someone of 25, she can have a face-lift. This way she becomes more attractive and then there is a chance that she might produce offspring again. But because of her age, the chance on mutations in her ova is larger and the offspring might have more unfavourable genes. When you undergo plastic surgery you modify your phenotype even though your genotype, possibly (partly) unfavourable, remains the same.
Some research indicates that an organ in the nose, the vomeronasal organ, can detect pheromones. Pheromones play a large role in partner selection in the animal kingdom. If we use deodorant or perfumes, we hide these pheromones and therefore partner selection based on these substances is disabled. These are just some examples of how we have disabled sexual selection.
Who adapts who?
But the problem goes back even further: we adapt nature to our needs. We can adapt faster than the natural selection. If we would not have done that, plastic surgery would not have made that much difference. For example, a woman who has undergone plastic surgery might not have been fit enough to run from a large man-eating predator because of her facelift: some stitches might snap or she would be simply too old to run fast enough. Therefore she would have had more chance of getting caught, which would, of course, not let her produce offspring. But this simply isn’t the case. There are no large man-eating predators any more in a large part of Europe and Northern America. The only threat we still have comes from untreatable diseases. And if we can’t treat these, we try to prevent them. We increase our hygiene, we kill carriers of diseases like mosquito’s and tics. We constantly adapt our surroundings.
Shortage of food or water is no big problem these days. We do not need to go out and catch food, it just lies in the supermarket down the street. If you are able to make it to the supermarket and back alive, you can survive. The supermarket will always have food. If there isn’t enough food of some kind, more farmland will be made out of nature. We don’t need to rely on rivers or springs. We drill wells, and if these are dried out, we just drill deeper.
We have become a very social species with a very complicated social system. We are the only species to have developed something like money, and money has a very big role in our modern society. Another very distinctive thing in our society is the caring for the less-fit, evolutionary speaking. We treat elders very well and we have all kinds of insurances. This is something you don’t see in nature and people who benefit these things, would otherwise have been subject to more natural selection.
The end of evolution?
Though it may seem as if we have slowed or even turned off evolution, this is not the case. One important point in evolution, mutation, does still happen in our body. This simply cannot be prevented. It may even happen at a higher rate because of damage to the ozone layer, more radiation and dangerous chemicals. All results of our intelligence. But it is the question if and how these mutations provide benefit to the individuals that have them. Perhaps mutations that make an individual smarter will become more important. Our modern society is, after all, a knowledge society. You cannot make much money these days without some kind of. And without money, you might not be able to pay treatment when you are ill.
Viruses will adapt to our antibiotics and other medicines (through natural selection). In fact, this has already happened: some strains of tuberculosis and other bacteria’s are immune to our antibiotics. If an individual is infected with such a bacteria, he or she will have to rely on the immune system, not on medical treatment.
Medical science is not perfect. There are many diseases that we can treat, but there also are many that we can’t treat or even prevent, SARS or Ebola, or diseases that we can only prevent, like HIV. Cancer is also a growing problem. One in three people in Holland will get cancer. Many kinds of cancer are treatable, if detected in an early stage. But if you are too late, your chances of survival will quickly decline. So even though diseases are not as dangerous to us as they were a century ago, they still pose a big threat to us.
There are still animals that also pose a threat to us, like snakes, sharks and other predators. We also have a climate which we cannot actively alter. When a group of tourists gets lost in the desert, it still is the fittest that will survive. But these animals and conditions are rarely found in the more civilized parts of the world. In development-countries, people are still much more subject to natural selection. They cannot afford medicines, even if they are available. In those countries, animals also pose a much larger threat to individuals.
We pose a big threat to ourselves. Things like shoot-outs, terrorism and war but also accidents and our effect on the climate let natural selection still act on us. Unfortunately not all of these are selective. A plane that crashes into a building, like on the 11th September, kills everyone in the building and the plane, not even the fittest will survive. But something like war is for a large part selective. As long as weapons of mass-destruction are not used, the better-trained and healthier soldiers have more chance of surviving the war.
Evolution is a very slow but flexible process, we have found ways to disable some kinds of natural selection, but we have created other kinds of natural selection. Evolution takes millennia and it will not become apparent what the effect of our high level of intelligence has on evolution.
When you look at the whole picture, it is better to say that man has won a battle in evolution, but the war is far from over. In fact, it may be that it has just begun…
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