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

If a trait exists in almost the entire population then it can be assumed that those that didn’t develop it died off before successfully breeding. The trait might not be useful anymore but it most certainly was at some point as evidenced by the lack of anyone without it.