No, Evolution is Not Random
And natural selection is not a chance process.

Posted December 3, 2021 | Reviewed by Kaja Perina

KEY POINTS

Evolution is not random, and natural selection is not a chance process.

The core mistake involves mixing up natural selection and mutation.

Resolving the confusion is key to understanding evolution and natural selection.

Have you ever come across a statement like this:

“I can’t believe that something as beautiful and complex as the human eye could be the result of a random process like evolution”?

Or this:

“It seems implausible that the intricate molecular machinery of the cell – a finely-tuned nanofactory of exquisite complexity – could have arisen by chance”?


The basic argument being made is as follows:

Premise 1. These complex, organized, functional parts of the body and brain could not possibly have arisen by chance.

Premise 2. Evolution is a chance process.

Conclusion: Therefore, these complex parts of the body and brain cannot be a product of evolution.

The fatal flaw in this argument is that premise 2 is incorrect. Evolution is not a chance-driven process; that is a widespread misconception.

To see why, we can break evolution down into two steps:

Step 1: Mutation. This step introduces new genetic variants into the population.

Step 2: Natural selection. In this step, some of these new genetic variants make it into the next generation, and some do not.

(This is a bit of a simplification, but it is good enough for our current purposes).

Step 1, mutation, is random. Mutations don’t arise in order to fill a current “need” of the organism. They are blind and they lack foresight, so they also can’t anticipate future needs. In this sense, they can reasonably be described as random. They can also be thought of as “random” in the sense that they are not automatically helpful; a new mutation may turn out to be beneficial or harmful or neutral.

However:

Step 2, natural selection, is not random at all. In fact, it is the diametric opposite of randomness. In this step, mutations that turn out to be beneficial to the organism are more likely to make it into the next generation precisely because they aid the organism’s survival or reproduction. Mutations that are harmful are less likely to make it into the next generation precisely because they lower the organism’s likelihood of survival or reproduction. If you give it a moment’s thought, you will see that this is the opposite of a random relationship. If something is random, it is inherently unpredictable and not orderly. Natural selection is the opposite. It is logical and predictable: the likelihood that a mutation will make it into the next generation depends, in a predictable way, on its effects on survival and reproduction. Beneficial mutations tend to get passed on, whereas detrimental ones are weeded out. This is a constrained and orderly relationship – the opposite of “randomness”.
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The core mistake is that people sometimes confuse mutations (which are random) with natural selection (which is not random). Evolution is a process in which randomly mutated genes pass through the highly non-random sieve of natural selection.

And because natural selection is quintessentially non-random, the functional products it shapes – such as the porcupine’s quill, the bombardier beetle’s defensive abilities, and the jewel wasp’s science-fictionesque hijacking of the cockroach’s mind – are also highly non-random.


So, yes: biological triumphs like the eye, the placenta, and the octopus’s three hearts could not have evolved by chance. And indeed, they didn’t. Mutation is random, but natural selection and evolution are not.


About the Author

Laith Al-Shawaf, Ph.D., is an associate professor of psychology at the University of Colorado. He studies emotions, cognition, and personality & individual differences.