Cousins: What the Great Apes Tell Us about Human Origins

On a sun-dappled East African morning four million years ago, several dozen small apelike hominids are foraging for plant foods in scattered forest along a river course when they come upon a large group of monkeys in an isolated tree. Some of the male hominids climb the tree, and although their upright posture and adaptation to ground living make them more at home there, through cooperative action some pursue the monkeys in the branches while others wait below. The monkeys scatter and try to flee, but several are caught in the tree crown while others fall to the ground; the