Sexual Selection Through Mate Choice
Every one of our ancestors managed not just to live for a while, but to convince at least one sexual partner to have enough sex to produce offspring. Those proto-humans that did not attract sexual interest did not become our ancestors, no matter how good they were at surviving. Darwin realized this, and argued that evolution is driven not just by natural selection for survival, but by an equally important process that he called sexual selection through mate choice.
from "The Mating Mind: How Sexual Choice Shaped the Evolution of Human Nature"
Quoted on Sun Feb 17th, 2013