Here's a fun evolutionary fact I like to throw out to people at times. You know our goose bumps that pop up when we're cold or scared or angry? Those are useless leftovers (vestigial reflexes) from our much hairier ancestors.
Not too much different from cats and other animals who get all 'poofy' when in the cold or fighting, these goose bumps raise hair on our skin when we're cold, to trap air, causing a layer of insulation, to keep us warm, and raise hair during emotional stress (when we're scared, angry, etc.) to make us look larger and more intimidating to ward off predators.
None of this is very helpful to us anymore, of course, but that doesn't make it any less fascinating.