The Story in Our Genes

Mention The Bell Curve in polite company these days, and it may not be polite for long. Critics have pummeled the best-selling book by Charles Murray and the late Richard Herrnstein, which blames genetics for the gap between the average I.Q. of whites and blacks. But most of the assailants haven’t noticed that perhaps their best weapon lies almost unused right under their noses. At about the same time that Murray threw his Curve, Princeton University Press put out The History and Geography of Human Genes by population geneticists Luca Cavalli-Sforza, Paolo Menozzi and Alberto Piazza. Not only is the tome physically hefty (1,000 pages, 7 1/2 lbs.), but the evidence it contains may carry enough weight to flatten Murray’s thesis once and for all.

While not exactly best-seller material, The History and Geography of Human Genes is a remarkable synthesis of more than 50 years of research in population genetics. It stands as the most extensive survey to date on how humans vary at the level of their chromosomes. The book’s firm conclusion: once the genes for surface traits such as coloration and stature are ) discounted, the human “races” are remarkably alike under the skin. The variation among individuals is much greater than the differences among groups. In fact, the diversity among individuals is so enormous that the whole concept of race becomes meaningless at the genetic level. The authors say there is “no scientific basis” for theories touting the genetic superiority of any one population over another.

The book, however, is much more than a refutation of the latest pseudoscientific pronouncement. The prime mover behind the project, Cavalli- Sforza, 72, a Stanford professor, labored with his colleagues for 16 years to create nothing less than the first genetic atlas of the world. The book features more than 500 maps that show areas of genetic similarity — much as contour maps match up places of equal altitude. By measuring how closely current populations are related, the authors trace the pathways by which early humans migrated around the earth. Result: the closest thing we have to a global family tree.

The information needed to draw that tree is found in human blood: the antigens, antibodies and other proteins that serve as markers to reveal a person’s genetic makeup. Using data collected by scientists over decades, the authors compiled profiles of hundreds of thousands of individuals from almost 2,000 communities and tribes. And to ensure a degree of “purity,” the study was confined to groups that were in their present locations as of 1492, before the first major migrations from Europe began — in effect, a genetic snapshot of the world when Columbus sailed for America.

Collecting blood, particularly from ancient tribes in remote areas, was not always easy; potential donors were often afraid to cooperate, or raised religious taboos. On one occasion, when Cavalli-Sforza was taking blood samples from schoolchildren in a rural region of the Central African Republic, he was confronted by an angry farmer brandishing an ax. Recalls the scientist: “I remember him saying, ‘If you take the blood of the children, I’ll take yours.’ He was worried that we might want to do some magic with the blood.”

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.

Now that Cavalli-Sforza’s mammoth study is finally complete, it’s time to start a fresh survey. Reason: new analytical techniques that in recent years have revolutionized the field of genetics. Instead of using indirect markers like blood groups, researchers can now determine the exact chemical sequences of long strands of DNA itself. Cavalli-Sforza and his colleagues believe this technology can be used to resolve questions they were ill-equipped to answer, such as the origins of the Negrito tribes in the Indian Ocean, Malayan peninsula and the Philippines. Anthropologists suspect that they are descendants of a wandering people who had once formed an ancient human bridge between Africa and Australia.

The daunting task of making a more refined genetic atlas now lies with the Human Genome Diversity Project (an offshoot of the ambitious Human Genome Project), which was set up by a committee of scientists chaired by Cavalli- Sforza. Its objective is to create a global data base over the next 10 years using the new techniques — and unlock more secrets of the human gene pool.

Before the researchers can even get started, however, they will have to confront some major questions: How will the genetic sequences be used, and who will benefit from them? Genetic information is the raw material of the burgeoning biotechnology industry, which uses human DNA to build specialized proteins that may have some value as disease-fighting drugs. Activists for indigenous populations fear that the scientists could exploit these peoples: genetic material taken from blood samples could be patented for commercial use without adequate compensation to the tribes that provide the DNA.

The researchers believe they can ease such concerns. Already, the Human Genome Diversity Project is working with a U.N. organization to establish some guidelines. Cavalli-Sforza stresses that his mission is not just scientific but humanitarian as well. The study’s ultimate aim, he says, is to “undercut conventional notions of race” that cause discrimination. It is a goal that he hopes will resonate among indigenous peoples who have long struggled for the same end.