The anthropologists John Tooby and Irven Devore have argued that millions of years ago our ancestors occupied the "cognitive niche" in the world's ecosystem. By evolving mental computations that can model the causal texture of the enviroment, hominids could play out scenarios in their mind's eye and figure out new ways of exploiting the rocks, plants, and animals around them. Human practical intelligence may have co-evolved with language (which allows know-how to be shared at low cost) and with social cognition (which allows people to cooperate without being cheated), yielding a species that literally lives by the power of ideas.

                               ---Steven Pinker, Chapter 13 "Out of Our Depths", Book "The Blank Slate"