Because of the scarcity of fossils and the discovery of
important new finds every few years, researchers disagree about
the details and sometimes even basic elements of human
evolutionary history. While they have revised this history
several times over the last decades, currently, researchers
agree that the first species of the genus Homo, Homo habilis,
evolved in Africa around two million years ago, and that members
of the genus migrated "out of Africa" somewhat later. The
descendants of these ancient migrants, which probably included
Homo erectus, have become known through fossils uncovered far
from Africa, such as those of "Peking man" and "Java man." The
Neanderthals are also considered the descendants of early
migrants. According to the single-origin model, however, every
species of the genus Homo but one was driven extinct: Homo
sapiens. This species evolved in Africa between 100,000 and
200,000 years ago and, in a second important exodus from Africa,
began colonizing the rest of the world some time aft