The whole system is made up of many parts. Your body is a result of all the tiny physical processes you are made up of. All the way down to the tiny essential functions that RNA performs so well. These small machines completing their own task form larger systems with emergent properties – making them more than the sum of their parts. And this is what makes evolutionary biology so unintuitive, because it appears creative when we see the incredible mechanisms organisms have developed in order to survive. (One of my favorites is shrews shrink their brains and skulls by 15% to conserve resources in the winter). In trying to figure out why bats have wings, you can’t start with the wing. Wings (in bats) are a form of emergence and not an end unto itself. It’s not that nature decided wings are helpful to grow because flying seems like an exceptional evolutionary trait. For bat wings to grow, the webbed-digit genes must become more and more frequent in successive generations. We have to be careful when inscribing purpose into the end traits; there’s no decision in which genes ought to be promoted. And a gene’s effect must cause copies of itself to become more frequent in the next generation. A chicken is an egg’s way of creating another egg, and we are a gene’s way of creating more genes.

It is amazing how similar all life on earth is, that we are all made from the same (cellular and genetic) legos. This is made even more stunning by the diversity on this planet. We can see amazing features that look like ends unto themselves, but really they are a result of a very long time of some tiny but non-zero statistical correlation between a gene and how often an organism reproduces. Take the amazing ability of human sight. It’s easy to see how sight is important in survivability and reproduction as well as bad puns. But if an engineer saw how the human eye was designed it would appear to be designed backwards. In the retina, the light sensitive cells are in the back and the nerves come out the front only to go back through the retina to the brain. This causes a blind spot. (Test your blind spot here). Some organisms like octopi have independently evolved their retina the other way around and as a result they have no blind spot. The eye is a complex system, so it can’t just be redesigned with a single genetic mutation. Fortunately it doesn’t matter too much because the other eye fills in the missing information.

Evolution is not creative or conscious, it has no foresight and is only building off that which it has now. It keeps building on a foundation that’s already there driving us toward more complexity. Technically it’s an open question whether evolution is directional and necessarily drives organisms to become more complex, but at the very least that’s the trend that most organisms have seen. Even though selection shouldn’t necessarily have any intrinsic direction (toward simplicity or complexity) it appears less likely evolution takes away building blocks as much as it adds on them. Or at least ignores them, in the case of vestigial structures.

Single-sentence refutation: It’s a good thing that evolution isn’t intelligent because there seems to be diminishing returns on intelligence in natural selection (or else everything would have evolved more intelligent?), just look at the existential threats humans have created… and still pigeons outperform us in some forms of statistical reasoning and chimpanzees outperform us in working memory.