How a Fickle Climate Made Us Human

摘要

Humans, like children, are the products of their environment. The famous anatomist Raymond Dart recognized that back in 1925, when he described the first hominin skull found in Africa. The evolution of this "Man-Ape," he wrote, markedly differed from that of earlier apes. While apes lolled about in "luxuriant" tropical forests that posed relatively few survival challenges, the "Man-Ape" had to compete for scarce food and water with saber-tooth tigers and other dangerous beasts of the arid savanna—and ended up sapient. "For the production of man a different apprenticeship was needed to sharpen the wits and quicken the higher manifestations of intellect—a more open veldt country," Dart wrote.This "savanna hypothesis" suggested that as a drier climate caused grasslands to spread, our ancestors moved out of the trees and began walking upright in order to spot predators and prey in the waist-high stems. That freed their hands to use tools and spurred the development of big brains.