why does natural selection make organisms have traits that are helpful but not necessary for the species’s survival?

Question

For example our hands become wrinkly after getting wet so our ancestors could grip onto trees better after swimming.

Would we really go extinct as a species if we didn’t develop that extremely specific trait at one point?

Same for crying as an emotional response, or eyebrows keeping sweat out of our eyes, or goosebumps making our hair stand to be more intimidating to predators.

I understand why these would be helpful, but I don’t see why these were so necessary to the human race’s continuation that nearly every human has these traits.

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Answer 1

Helpful for survival is occasionally necessary for survival. Humans could all be myopic and we’d mostly survive, but some people *would* die because of it.

It doesn’t have to mean life or death for everybody, just for enough people over millions of years.