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” often means breeding earlier, breeding more often, breeding for longer, having healthier children, being able to raise more children without overextending yourself, being able to help your children raise their children because you live longer etc. An advantage over other members of your species means that your genes will be more prevalent in the population.