Leading scientists and creative thinkers were asked to address this question. My favorite answer was from Judith Harris:
I believe, though I cannot prove it, that three – not two – selection processes were involved in human evolution.
The first two are familiar: natural selection, which selects for fitness, and sexual selection, which selects for sexiness.
The third process selects for beauty, but not sexual beauty – not adult beauty. The ones doing the selecting weren’t potential mates: they were parents. Parental selection, I call it.
Nicholas Humphrey gave another good answer:
I believe that human consciousness is a conjuring trick, designed to fool us into thinking we are in the presence of an inexplicable mystery. Who is the conjuror and why is s/he doing it? The conjuror is natural selection, and the purpose has been to bolster human self-confidence and self-importance – so as to increase the value we each place on our own and others’ lives.
Addendum: Eric Crampton points me to 120 additional answers, including Jared Diamond, Steven Pinker, and many other notables. My answer? I will go with Denis Dutton, with honorable mentions to Robert Trivers and Alexander Vilenkin. I like Carlos Rovelli too. Yes I know you don’t all click on all of the links but these are worth checking out.