This post is an explanation (though non-technical) of how evolution actually works, in contrast to how most people think about it.
Note that I am not aware of how prevalent is the misunderstanding this post attempts to correct. It is possible that fewer people are under the misunderstanding than I think. I decided to write about it because most people around me aren't aware of the actual evolution mechanism. Moreover, I remember how it was taught to me in school, and the way it was taught was misleading. If that's how evolution is still taught then I believe this post will be useful in clarifying the mechanism.
Common notion of evolution is that organisms adapt to suit their environment. Wrong!
Organisms don't adapt to suit their environment. Random mutations are always happening in organisms, but only those mutations are successful which produce alterations which are allowed to continue by their current environmental conditions. When the process of certain alteration is complete it appears as if the change of feature in a particular organism happened to suit the environment. But the fact is, mutations for that same change may have happened many times in the past, but only this time the environmental conditions were favorable for the organism with altered feature to survive, and thus for the altered feature to become normal.
Confused? Take the example of giraffe's neck. It is mostly taught in schools (at least in my school it was taught so) that giraffe's neck became long because they moved from savannah (grassland) to the areas with tall trees in times of food scarcity. A long neck was required for them to reach the leaves high up the trees. Hence, over many generations through evolution their neck became long! This is an oversimplification of the process of natural selection. It gives an impression that environmental changes precede alterations in organism's features. In reality it is not quite so.
Let's see what's happened in case of giraffe's neck. Long neck resulted in giraffes through many mutations over time. The contribution of each single mutation is understandably only slight. And such mutations take place from time to time "randomly" regardless of environmental conditions, not only for neck but for all sorts of alterations in an organism. With respect to the above hypothesis, here's what must have happened considering how evolution actually works: When giraffes were living in savannah they did not require long neck. Rather, long necks might have posed danger to their survival by making them noticeable to predators from a distance. So, whenever the random mutation for long neck happened, the giraffe with newly acquired slightly longer neck would be hunted down by the predator (owing to its long neck) and the mutation thus would go unsuccessful since the animal wouldn't pass on its genes for long neck! Now, say, the giraffes have shifted from grasslands to the forests with tall trees. Random mutation for long neck happens again. (Mutations always keep happening randomly!) This time the giraffe with slightly long neck survives, and reproduces! Because in their new environment, long neck doesn't attract predators' notice. And with further random mutations for long neck, over many generations, the neck goes on increasing as long as the environmental conditions don't restrict it by putting the giraffe at a disadvantage for survival and/or reproduction. Moreover, in the areas with tall trees those giraffes with short necks become disadvantaged because they can't get food easily. The disadvantaged giraffes wouldn't be able to pass on their genes (of short neck) because they would starve and die before reproducing. It is thus said that giraffes with long necks are selected by natural selection. Of course, this process happens over long time period. (Note that this is the simplest of the hypotheses about giraffe's neck. Even if it may not be quite true in giraffe's case, it's nonetheless valid as to the point being explained.)
Let's have a look at another example. You must have seen albino people. Albinism also has emerged by random mutation, without the environment demanding it. But albinos are not common in population precisely because they are at a disadvantage in survival and reproduction. Albinos being vulnerable to harmful ultraviolet rays, and thereby skin cancer, and faring poor at finding a mate to reproduce with, restricts the genes of albinism to spread. If in the future, say, Earth's environment so changes that we no more face ultraviolet rays then randomly born albinos will have better chances of survival, and it is possible that in the long term albinism will spread enough to become a normal feature of human species! Likewise, we have every reason to think that many other alterations in human species are happening from time to time by way of random mutations, without the environment requiring it. But only those changes which don't put the bearer of the change at a disadvantage in his/her environment pass further on and become a normal feature after many generations of evolution.
The important, and often misunderstood, point about the process is this: Changes in environmental conditions don't precede alterations of features in organisms. Random mutations are always happening, and environment only allows or disallows the genes of altered features to go further. When the alteration is allowed by the environment the newly evolved feature is spread further through reproduction in the organism. When the alteration puts the organism to disadvantage in its current environment, the organism wouldn't survive and the altered feature would therefore never become normal.
In short, environment doesn't bring about the change in features. It only approves or disapproves the changes that happen on their on randomly!
Note that I am not aware of how prevalent is the misunderstanding this post attempts to correct. It is possible that fewer people are under the misunderstanding than I think. I decided to write about it because most people around me aren't aware of the actual evolution mechanism. Moreover, I remember how it was taught to me in school, and the way it was taught was misleading. If that's how evolution is still taught then I believe this post will be useful in clarifying the mechanism.
How Evolution Actually Works
Common notion of evolution is that organisms adapt to suit their environment. Wrong!
Organisms don't adapt to suit their environment. Random mutations are always happening in organisms, but only those mutations are successful which produce alterations which are allowed to continue by their current environmental conditions. When the process of certain alteration is complete it appears as if the change of feature in a particular organism happened to suit the environment. But the fact is, mutations for that same change may have happened many times in the past, but only this time the environmental conditions were favorable for the organism with altered feature to survive, and thus for the altered feature to become normal.
Confused? Take the example of giraffe's neck. It is mostly taught in schools (at least in my school it was taught so) that giraffe's neck became long because they moved from savannah (grassland) to the areas with tall trees in times of food scarcity. A long neck was required for them to reach the leaves high up the trees. Hence, over many generations through evolution their neck became long! This is an oversimplification of the process of natural selection. It gives an impression that environmental changes precede alterations in organism's features. In reality it is not quite so.
Let's see what's happened in case of giraffe's neck. Long neck resulted in giraffes through many mutations over time. The contribution of each single mutation is understandably only slight. And such mutations take place from time to time "randomly" regardless of environmental conditions, not only for neck but for all sorts of alterations in an organism. With respect to the above hypothesis, here's what must have happened considering how evolution actually works: When giraffes were living in savannah they did not require long neck. Rather, long necks might have posed danger to their survival by making them noticeable to predators from a distance. So, whenever the random mutation for long neck happened, the giraffe with newly acquired slightly longer neck would be hunted down by the predator (owing to its long neck) and the mutation thus would go unsuccessful since the animal wouldn't pass on its genes for long neck! Now, say, the giraffes have shifted from grasslands to the forests with tall trees. Random mutation for long neck happens again. (Mutations always keep happening randomly!) This time the giraffe with slightly long neck survives, and reproduces! Because in their new environment, long neck doesn't attract predators' notice. And with further random mutations for long neck, over many generations, the neck goes on increasing as long as the environmental conditions don't restrict it by putting the giraffe at a disadvantage for survival and/or reproduction. Moreover, in the areas with tall trees those giraffes with short necks become disadvantaged because they can't get food easily. The disadvantaged giraffes wouldn't be able to pass on their genes (of short neck) because they would starve and die before reproducing. It is thus said that giraffes with long necks are selected by natural selection. Of course, this process happens over long time period. (Note that this is the simplest of the hypotheses about giraffe's neck. Even if it may not be quite true in giraffe's case, it's nonetheless valid as to the point being explained.)
Let's have a look at another example. You must have seen albino people. Albinism also has emerged by random mutation, without the environment demanding it. But albinos are not common in population precisely because they are at a disadvantage in survival and reproduction. Albinos being vulnerable to harmful ultraviolet rays, and thereby skin cancer, and faring poor at finding a mate to reproduce with, restricts the genes of albinism to spread. If in the future, say, Earth's environment so changes that we no more face ultraviolet rays then randomly born albinos will have better chances of survival, and it is possible that in the long term albinism will spread enough to become a normal feature of human species! Likewise, we have every reason to think that many other alterations in human species are happening from time to time by way of random mutations, without the environment requiring it. But only those changes which don't put the bearer of the change at a disadvantage in his/her environment pass further on and become a normal feature after many generations of evolution.
The important, and often misunderstood, point about the process is this: Changes in environmental conditions don't precede alterations of features in organisms. Random mutations are always happening, and environment only allows or disallows the genes of altered features to go further. When the alteration is allowed by the environment the newly evolved feature is spread further through reproduction in the organism. When the alteration puts the organism to disadvantage in its current environment, the organism wouldn't survive and the altered feature would therefore never become normal.
In short, environment doesn't bring about the change in features. It only approves or disapproves the changes that happen on their on randomly!
|
|
0 Comment(s):
Post a Comment
Please preview and double-check your comment before posting. View comment policy.