|Genes, Peoples, and Languages|
|by Luigi Luca Cavalli-Sforza|
Posted: September 8, 2000
Instead of depending solely on chance finds of random remains, science has now uncovered a far more powerful and reliable record of the human past, as Luigi Luca Cavalli-Sforza shows in his concise and provocative introduction to a field that could accurately be called genetic archeology. In every cell of our body, each of us carries genes passed down to us from the countless generations of our ancestors. Coded within these genes is a history of where those ancestors were, what conditions they faced, and how they adapted to them.
Natural selection favors genes that aid survival in the particular circumstances in which a group lives. Pale skin, for example, helps people get enough vitamin D in lands with scant sunlight. Possessing a single sickle cell gene aids in resisting malaria. Different places present different challenges, so natural selection favors different genes in the tropical jungle, arctic tundra or temperate pastureland. Over generations, therefore, the genomes of groups living in different areas will diverge, as will some of their characteristics. Enhancing this separation is genetic drift, the scientific name for the random variations in gene frequencies that happen over time as genes are sorted and resorted in very small populations. Because humans lived in little groups for the great majority of time as a species, drift has played a large role in differentiating populations.
Studying the differences among the genomes of dispersed groupsin scientific parlance, the genetic distance between themcan, Cavalli-Sforza shows, reveal a great deal about the people's past. Exactly how these calculations work is highly technical, and this brief volume does not, unfortunately, provide Cavalli-Sforza enough room to explain them in satisfying detail. But for readers either highly versed in statistics or willing to take his word that the methods are in fact reliable, he lays out a fascinating and persuasive epic of human migration and settlement.
Genetic and other information convincingly indicates that all living humans descend from people who emerged in Africa hundreds of thousands of years ago. Somewhere between 50 and 100 millennia back, people began to expand into western Asia. In time, the spread continued eastward, northward and southward. Some of their descendants colonized the Indian subcontinent and Southeast Asia, moving on to Australia and the Pacific. Others filled Central Asia and spread on to the east, eventually reaching the Americas. Yet others moved up through the Middle East into Europe and some reached the same destination by moving westward across the Asian steppes. This chronology also receives remarkably robust support from linguistic studies, Cavalli-Sforza shows. Languages, like populations, have evolved over time and their similarities and differences also tell much about the relationships among the peoples speaking them. The traditional studies of bones and stones by both cultural archeologists and physical anthropologists provide further corroboration.
Distilled from an enormous mass of data in half a dozen disciplines, the conclusion emerges that the traits supposedly differentiating distinct racial typesskin color, hair texture, nostril size, eye shapeare, both literally and figuratively, superficial. They constitute surface adaptations to climatic differences rather than thoroughgoing distinctions in basic qualities and they involve "most likely only a small bunch of genes." (p. 13). Nor do these adaptations occur in sharply defined types but rather they vary across the world along many gradients. Despite the various visible and invisible differences among groups, the genetic similarities among today's billions of descendants of those ancient Africans outweigh the surface differences so overwhelmingly that genetically "homogeneous races do not exist." (p. 13).
The fact that this and the author's other conclusions arise from data provided by a large number of independent disciplines gives them real force. But the fact that the author must acquaint the reader with the concepts and methods of so many fields in so little space produces some explanations that feel superficial, vague, even naive. The further Cavalli-Sforza gets from his own field of genetics, the flimsier his capsule synopses seem; and his musings on social change, for example, come nowhere close to the level of the rest of the book.
But this is an honorable fault arising not from mediocrity or sloth but from intellectual boldness and lofty ambitions. Cavalli-Sforza has undertaken to do several hard tasks in a single, small volume: to introduce the general reader to a vast and fascinating field of research, to lay out its major conclusions thus far, and to accomplish this in clear enough language and few enough pages to keep the general reader's interest. Succeeding admirably in these attempts, he produced a book that will change the way readers think about their fellow humans and common human history.
Beryl Lieff Benderly, a freelance writer in Washington, DC, is a member of the board of the National Association of Science Writers.