“Is natural selection random?”

One of the most common series of search terms that gets people to FTSOS is the title of this post. Most people end up clicking my article on why natural selection is not random; I’m not a huge fan of that piece. It was originally written for a local weekly paper (which changed ownership as I finished), not a blog. What’s more, it is very far from being succinct. I want to rectify that issue in this post.

So is natural selection random? No. Why not? The answer is simple: Natural selection is the pressure placed on a population and the change that happens in response to that pressure. Whereas the exact pressure is in part random in regards to any given population, exactly how a population responds follows some basic rules. Now, the reason I say the pressure is only random “in part” is because first and foremost I’m referring to changes in the environment that happen without regard to life. The rising of a mountain range is one example. But at the same time, other changes that might occur are in response to the direction of a population. For instance, it often pays to be the biggest and baddest member of a species for males, but instead of responding by becoming all the bigger and badder, some members might just become tricky. Some octopi, for example, will trick guardian males into believing they are just another female, gaining them access to the real female. This pressure isn’t entirely random since it is a response to the evolutionary state of a population. That is, becoming tricky is a response to being big and bad, and becoming big and bad was not itself random. But why? Well, I’m glad you asked:

Selection is a biased reaction to a given environment. This is specifically with regard to life: those that are able to exploit their environment best (and I really just mean ‘well enough’) are the ones that are going to survive. If it was all just random, then we would see no bias: We wouldn’t see a species trend in one way or another, beneficial genes would hardly ever become common, and we would never be able to make predictions. But what we see are trends and an increase in beneficial genes (and the elimination of deleterious genes) and we make predictions all the time. It is because of biased genetic reactions in populations that we call natural selection non-random.

I wouldn’t mind going on and on, but I said I want to make this succinct, so I will end with just one final but important point: The non-biased genetic reactions that happen because of natural selection must be measured across a population and through generations. If a creationist someone starts talking about natural selection being random and pointing out individual responses to the environment, then we might not be talking about the same evolutionary mechanism anymore. Everything that happens within evolution is happening to populations. Individuals do not evolve. So natural selection is the differential survival of individuals (or genes, depending on your perspective), but it is measured through time and within the context of a population.

It still isn’t random

This is apparently some confusion over my post about why natural selection is not random. It’s a fairly elementary issue at hand, but it evidently needs to be addressed. One reader mentions,

Natural selection is a product of selective pressures. Those selective pressures are random in that they do not try to produce anything specific (ie: original appendages, limbs, organs, organ systems, body plans, etc… or the DNA that codes for them).

This user is right so far, even if the language is a bit dicey. A particular environment produces conditions to which a population then responds. A research job from a biology professor of mine will do fine here: there are two species of fish in a stream, one small, one large. This stream is divided into two sections: an upper area and a lower area. The division is due to a small waterfall. Now, the small fish in the top section of the stream tend to be vibrant in color while the lower small fish are a more gray color. The hypothesis is that the large species of fish is unable to traverse the waterfall so thus unable to eat the upper small fish, hence their vibrancy. So the research team takes some large fish and introduces them into the area with the vibrant fish. Sure enough, the fish lose their vibrancy pretty quickly. Conclusion: The hypothesis was not falsified because a correlation between color vibrancy and survival was shown upon introduction of the large fish species to the upper stream.

So now here’s where the user goes awry.

Hence, natural selection is random.

He concludes that because the selective pressures happen without regard to a particular species that the reaction of the species is thus random. Do you see the inane logic? This is like saying that because what particular rocks, gas, and space junk goes into the making of a planet can be called random that the force behind the accretion process – gravity – is random.

It’s all very simple. Natural selection is the process of differential survival of organisms based upon how they respond to a given environment. That means that natural selection happens with regard to adaptability. And maybe this is the kicker for this silly creationist. That’s really all “non random” means – with regard to adaptability. That’s why any aspect of genetic drift or mutation is considered random. It happens regardless of whether an organism will do better, worse, or the same in its survival. Were natural selection random then we should expect to see a number of vibrant fish swimming around the upper stream which is in comparable proportion to the number swimming around prior to the introduction of the large fish species. Of course we do not see anything like that. What we do see is differential survival based upon the response of the organism to a particular environment – the fish which survived were less vibrant, on average, than the fish which were quickly eaten.

It still isn't random

This is apparently some confusion over my post about why natural selection is not random. It’s a fairly elementary issue at hand, but it evidently needs to be addressed. One reader mentions,

Natural selection is a product of selective pressures. Those selective pressures are random in that they do not try to produce anything specific (ie: original appendages, limbs, organs, organ systems, body plans, etc… or the DNA that codes for them).

This user is right so far, even if the language is a bit dicey. A particular environment produces conditions to which a population then responds. A research job from a biology professor of mine will do fine here: there are two species of fish in a stream, one small, one large. This stream is divided into two sections: an upper area and a lower area. The division is due to a small waterfall. Now, the small fish in the top section of the stream tend to be vibrant in color while the lower small fish are a more gray color. The hypothesis is that the large species of fish is unable to traverse the waterfall so thus unable to eat the upper small fish, hence their vibrancy. So the research team takes some large fish and introduces them into the area with the vibrant fish. Sure enough, the fish lose their vibrancy pretty quickly. Conclusion: The hypothesis was not falsified because a correlation between color vibrancy and survival was shown upon introduction of the large fish species to the upper stream.

So now here’s where the user goes awry.

Hence, natural selection is random.

He concludes that because the selective pressures happen without regard to a particular species that the reaction of the species is thus random. Do you see the inane logic? This is like saying that because what particular rocks, gas, and space junk goes into the making of a planet can be called random that the force behind the accretion process – gravity – is random.

It’s all very simple. Natural selection is the process of differential survival of organisms based upon how they respond to a given environment. That means that natural selection happens with regard to adaptability. And maybe this is the kicker for this silly creationists. That’s really all “non random” means – with regard to adaptability. That’s why any aspect of genetic drift or mutation is considered random. It happens regardless of whether an organism will do better, worse, or the same in its survival. Were natural selection random then we should expect to see a number of vibrant fish swimming around the upper stream which is in comparable proportion to the number swimming around prior to the introduction of the large fish species. Of course we do not see anything like that. What we do see is differential survival based upon the response of the organism to a particular environment – the fish which survived were less vibrant, on average, than the fish which were quickly eaten.

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