[ThrustVectoring]

Evolution does not understand and does not optimize for the survival and flourishing of a species. There are three reasons why members of a species vary - either the variance is the result of a beneficial gene, or it's the result of random changes to irrelevant genes, or the species is partway through fixing a new beneficial mutation through the entire population.

So the more complicated explanation as to why humans vary is that humans have a specific set of adaptations for learning and filling their place in the social environment. This is the entire point of childhood - trying things, seeing what works well, doing more of it, and winding up a person who does the sorts of things that work well for them. This means that if you happen to be gifted with bad eyesight and good verbal processing, you'll get early successes at storytelling that lead you to that sort of role as an adult.

That, in a nutshell, is why humans have such variance. It's the result of childhood, which is a specific algorithm that genes use to find and exploit the things the hosts happen to be better at.

And this built-in ability to vary oneself is helpful both for the strong and the weak, the pretty and the ugly, the clever and the dull, and so forth. It means instead of over-fitting for behaviors that work for the strong, the trait enacts a strategy that does strong-person behavior in strong people and weak-person behavior in weak people.