Primates, the mammalian family of which we are a member, first appeared at the beginning of the Cenozoic Era, some 65 million years ago. Within 5 million years, ancestral primates had diverged into the prosimians (future lemurs, lorises, galagos and pottos) and the anthropoids (future monkeys, apes and humans). Both branches were successful for the next 20 million years but, with the appearance of true monkeys, 40 million years ago, the prosimians began to decline; today, survivors of that group are in isolated areas (e.g. Mada-gascar) or have adopted a nocturnal lifestyle, reducing their need to compete with monkeys.
Apes evolved in Africa 10 million years ago; gorillas diverged from the human line about 9 million years ago and chimpanzees broke away 7 million years ago. Our earliest humanoid ancestors (found to date) are the Australopithecies, which appeared in the Rift Valley of East Africa some 4.5 million years ago; males of these species weighed about 100 pounds, twice as much as the females. Homo habilis appeared in Africa about 2.5 million years ago and was the first hominid to use stone tools. Neither of these early hominids ever migrated from Africa.
At the onset of the Pleistocene, 2 million years ago, Homo erectus evolved in Africa. Males were about 5.5 feet tall and this species had a pelvic structure that favored an upright posture. His hand anatomy permitted a precision grip and he was the first hominid to control and use fire (a skill learned some 1.5 million years ago). Homo erectus was also the first human ancestor to leave Africa, spreading through southern Asia within 200,000 years of his evolution. About 200,000 years ago, Homo heidelburgensis appeared in East Africa; one branch of this species, which migrated northward into western Asia and Europe, would become the Neandertals while the second branch, which spread through sub-Saharan Africa, would give rise to Homo sapiens (modern man). By the end of the Pleistocene, 10,000 years ago (and 115,000 years after he first appeared), man had spread to every Continent except Antarctica.
