(2 of 3)
Despite the difficulties, the scientists made some myth-shattering discoveries. One of them jumps right off the book's cover: a color map of world genetic variation has Africa on one end of the spectrum and Australia on the other. Because Australia's aborigines and sub-Saharan Africans share such superficial traits as skin color and body shape, they were widely assumed to be closely related. But their genes tell a different story. Of all humans, Australians are most distant from the Africans and most closely resemble their neighbors, the southeast Asians. What the eye sees as racial differences -- between Europeans and Africans, for example -- are mainly adaptations to climate as humans moved from one continent to another.
The same map, in combination with the fossil record, confirms that Africa was the birthplace of humanity and thus the starting point of the original human migrations. Those findings, plus the great genetic distance between present-day Africans and non-Africans, indicate that the split from the African branch is the oldest on the human family tree.
The genetic atlas also sheds new light on the origins of populations that have long mystified anthropologists. Example: the Khoisan of southern Africa (Bushmen and Hottentots). Many scientists consider the Khoisan a distinct race of very ancient origin. The uniqueness of the clicking sounds in their language has persuaded some linguists that the Khoisan are direct descendants of the most primitive human ancestors. But their genes beg to differ. They show that the Khoisan may be a very ancient mix of west Asians and black Africans. A genetic trail visible on the maps shows that the ancestral breeding ground for this mixed population probably lies in Ethiopia or the Middle East.
The most distinctive members of the European branch of the human tree are the Basques of France and Spain. They show unusual patterns for several genes, including the highest rate of the Rh-negative blood type. Their language is of unknown origin and cannot be placed within any standard classification. And the fact that they live in the region adjoining the famous Lascaux and Altamira caves, which contain vivid paintings from Europe's early hunter- gatherers, leads Cavalli-Sforza to a tantalizing conclusion: "The Basques are extremely likely to be the most direct descendants of the Cro-Magnon people, among the first modern humans in Europe." All Europeans are thought to be a hybrid population, with 65% Asian and 35% African genes.
In the Americas, a look at native tribes showed that they were not all blood brothers. The three main groups, classified by language, were found to be genetically distinct, suggesting that three separate populations from Asia may have crossed the Bering Strait at different times to settle in America. The Amerind, who predominate in most of North and South America, possess only type O blood; among the Na-Dene, who cluster in Alaska, Canada and the U.S. Southwest, O prevails but A makes an appearance; in the Alaskan and Canadian Inuit (Eskimo), A, B, AB and O blood groups show the pattern seen in the rest of the world.