Why Are Humans So Much Smarter Than Other Species?

David Geary says humans became much smarter than other species because brain expansion, new tools, and conflict between growing populations reinforced one another. Humans are unusual in brain size, in learning novel things such as reading, writing, inventing, and mathematics, and in self-awareness. The question is the subject of his book The Origin of Mind, which he is revising. He starts about four or five million years ago with early relatives that include Lucy, whose brains were only a little bigger than chimpanzees' and grew gradually. A little over two million years ago, maybe two and a half, Homo habilis, a tool maker, shows a jump in brain volume. The larger jump is Homo erectus, about 1.8 or 1.9 million years ago, with bigger bodies and more brain.

Tools, better hunting, and cooking brought more calories, which cut mortality and grew the population. Bigger populations meant fewer resources per person and more competition inside the group, and expansion into other groups' territory followed. He says the archaeology shows more conflict and violence. When at least eight Homo species shared an area, the chance that one or several went extinct went up. Humans later moved into Eurasia about 60,000 years ago, after Neanderthals had held them in check, and he says that record shows a lot of violence too, along with some interbreeding.