FOSSIL VERTEBRATES/Hominids 543 Figure Reconstruction by the late Maurice Wilson of Homo habilis, based on 1.9 Ma individuals from Kenya and Tanzania Homo sapiens Figure Reconstruction by the late Maurice Wilson of Homo erectus from 450 Ka individuals at Zhokoudian Cave, China Homo sapiens probably evolved from H heidelbergensis at about 300 Ka, somewhere in eastern Africa It is difficult to be sure whether the transition between H sapiens and its ancestors was sudden or took place over a relatively long time period They differ from their ancestors in having a much larger brain size and in the virtual absence of a brow ridge They spread into the Middle East at about 100 Ka, and on into southern Europe relatively quickly after that Migration to northern Asia appears to been have later (the earliest humans in China date from about 50 Ka) The oldest human remains in Australia also appear to date from about 50 Ka Much later, humans colonised the Americas via the Siberian land bridge during a sea-level low stand before 13 Ka Once in America they spread quickly, reaching Patagonia in southernmost South America at about 11 Ka Differentiation between the various human racial types (African, Caucasian, etc.) occurred through separation of the breeding populations, but the process has not gone so far that we have ceased to be a single biological species A key change in the behaviour of humans was the transition, which was progressive over a long time