For many thousands of years, Homo Sapiens and the other hominids lived side by side in Africa as elsewhere. By ten thousand years ago, however, all the hominids had disappeared. Scholars believe that this was the result of the gradual absorption of all the other hominids by the more biologically advanced Homo Sapiens. This process may explain the appearance of variations within Homo Sapiens. At various times and places, as Homo Sapiens absorbed other hominid strains, differences within Homo Sapiens developed. In any case it is clear that the various types of man came into existence very early. In Africa, this process led to the development of three main types: the brownish-yellow Bushmen in the south, the darker Negroes throughout most of the continent and the Caucasoid Mediterranean types in the north. Most of the concepts, held even by scholars about the nature and origin of races, are being proven inaccurate. Anthropological literature used to suggest that skin color in some groups was a possible indication of Mongoloid influences or that the thin, straight lips common in another group could be envisioned as a Caucasoid feature. However, it has become increasingly obvious that an analysis based on specific single traits such as these is always a poor indication of either racial origin or of racial contact. In fact, they could just as likely be the result of spontaneous and local variations within a given population grouping. In contrast, recent anthropological research is putting less emphasis on bone measurement and shape and, instead, is turning increasingly to technical analysis particularly through the examination of blood types. Making and using tools are what differentiate man from animals. The earliest tools which have survived the wear of time were made of stone. As man's techniques of handling stone improved, so did his tools. The hand axe, a large oval of chipped flint varying in size and weight, came into common usage about half a million years ago, and it has been found in much of Europe, Asia, and Africa. This too seems to have had an African origin. While scholars are not certain about its use, it was probably used for killing animals and for chopping meat.