The subtribe Australopithecines arose 4 million years ago, diverging into robust ("Paranthropus") and gracile ("Australopithecus") branches. The earliest documented representative of the genus "Homo" is "Homo habilis", which evolved around 2.8 million years ago from "Australopithicus". The brains of "H. habilis" were about the same size as that of a chimpanzee, and their main adaptation was bipedalism. During the next million years a process of encephalization began, and with the arrival of "Homo erectus", cranial capacity had doubled. "H. erectus" were the first of the hominina to leave Africa, between 1.3 to 1.8 million years ago.