“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.

One Response

  1. I have two things to say about this post. The first is that you make it sound a bit that the reaction of the population is willful or concious, which, of course, it is not.

    The second comment is to enhance the understanding of what is random and what is not. A species can have random changes to alleles and sometimes it can even have opposite changes simultaneously. For example, a mammallian species might have brown fur. Random allele changes might give some individuals lighter colored fur and some darker color fur. If the environment is stable, then both of these changes could be benign, but if the climate changes to become much warmer or much cooler, then natural selection could result in one allele becoming much more prominent than the other over time in the population this is neither random or willful. It is a resulting process due to stimulus and reactiveness.

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