How did humans evolve?

by Richard D. Alexander

The most mysterious and compelling unanswered question about ourselves is how we came to be. What caused us to evolve our marvelous intellects and our unsurpassedly complex social life? Why are we so different from our closest relatives? What happened to all of our extinct ancestors? Why is it that during the several million years since hominids diverged from the ancestors of modern apes, while other rapidly evolving forms of life were speciating prolifically, no part of the evolving human line has survived as - or possibly even became, contemporaneously with other incipiently human species - a different species? Why are we all alone at the pinnacle of the particular direction of rapid evolutionary change that led to the combining of such traits as a huge brain, complex intellect, upright posture, concealed ovulation, menopause, virtual hairlessness, a physically helpless but mentally precocial baby, and above all our tendency and ability to cooperate and compete in social and politica