"Humans weren't always human in this third sense, as far as we can tell. In the beginning, Homo sapiens seems not to have created art, played music, invented new tools, worked out the motions of the planets, or worshiped gods in the celestial sphere. These capacities accumulated slowly, over tens of thousands of years. Sometimes a new trait--a new kind of art, a new kind of construction--arose, only to fade out. But over the long run, as the other human species disappeared, these attributes built up in us, until perhaps fifty thousand years ago something resembling modern humankind--"behaviorally modern" humans, in the jargon--was loose in the world."