Eli5 : why do humans look different but animals and other species look the same?
In: Earth Science
Part of it is that we rapidly spread into every imaginable ecosystem on the planet, faster than evolution could cause us to drift far enough apart to create new human species. Every human now alive descends directly from one of 3,000-10,000 ancestors who survived a population bottleneck about 70,000 years ago, which is an eyeblink in evolutionary time for a species like us. That narrowed our potential for speciation quite a lot.
However, a larger part of it is in how your brain works. We have an entire section of our brain dedicated solely to recognizing faces. It’s one of the few which sort of works as intended immediately after birth, as anyone who has ever smiled at an infant only for them to smile back can attest. They can only do that because they are recognizing faces on an instinctual level. What this means in a practical sense is that your brain is incredibly good at identifying faces, and indentifying differences between them. Why we do this is obvious – being able to tell people apart is a powerful survival trait – but it’s very narrowly focused. It works best on human faces because it’s been trained almost entirely on them, to notice the kinds of differences which are common between human faces.
So there isn’t much variation between humans, but that which exists is super obvious to us because it needed to be to promote survival.
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