Luigi Luca Cavalli-Sforza, Professor Emeritus of Genetics at Stanford, has published prolifically in human genetics, evolution, and human population displacement. Among his works are The History and Geography of Human Genes (1994) and The Great Human Diaspora (with Francesco Cavalli-Sforza, 1995). This volume unites six lectures delivered at the Collège de France in 1981 and 1989 and subsequently published in France, then Italy. The author updated this English text, which Mark Seielstad produced from the French and Italian versions. Spanish and German editions already exist as well. Thus, this book on human patterns of evolution and migration in populations and languages has itself passed through major mutations on its way to readers.
A brief preface explains the author’s interdisciplinary point of view and aim to unite data from genetics, archaeology, and linguistics toward one understanding of humanity. He asserts that perceived “racial” differences are only superficial. As he opens “Genes and History,” the first essay, he considers the play Copernicus (1836) by Italian poet Giacomo Leopardi, an allegory in which the sun, tired of running about the earth, demands to stand still at the center of the solar system. Leopardi offers Cavalli-Sforza an oblique means to raise the theme of ethnocentrism: Everyone wants to be the center of the solar system. It is a human trait to value one’s own people and perhaps to express that pride through a belief in innate, biological superiority.
True, inherited racial differences, as opposed to acquired cultural differences, must be in the genes and accessible to analysis there. However, Cavalli-Sforza explains that many visible racial characteristics, such as skin color and even body conformation, are survival factors in different climates where distinct “racial groups have flourished. For example, dark skin protects against tropical sun and is found in genetically diverse populations from Africa to Australia, while the fair skin of northern Europe allows the absorption of sunlight and production of vitamin D.”
The true, inherited distinctions are hidden from casual view: One of the earliest recognized markers is the division of humanity into distinct blood-type groups. The proportion of different blood groups varies markedly across the major continental populations. Native Americans are the most extreme case: 98 percent have type O blood, with type A in less than 3 percent. Almost two-thirds of Europeans (65 percent) have type O blood; 27 percent have type A and 8 percent type B. Cavalli-Sforza uses this genetic marker (accessible for quantitative study without actual analysis of the genome) to suggest a reconstruction of human evolution through statistical analysis and study of large populations.
The advantage of blood types is the sheer volume of reliable data; the greater the pool of data, the more valid the results. Cavalli-Sforza raises and explores questions of statistical validity, discussing which graphical models best present each category of data and which models complement one another in presenting different aspects of the information. In the second chapter, “A Walk in the Woods,” he couples the topic of genetic differences of the indigenous populations of the world’s continents with the suitability of different tree charts to represent those differences.
Data quantity is vital here: Genetic data from living populations is abundant, while the fossil record is scanty and fragmentary and thus unsuited for statistical analysis. Cavalli-Sforza first presents his data in a table of percentages, then presents those percentages spatially in tree models: The smallest genetic distance lies between Asians and Native Americans (8.9), the greatest between Africans and Oceanians (24.7). Cavalli-Sforza compares what is shown in the archaeological record to the results of his statistical studies and argues that the patterns are very similar.
The inherent difficulties of extrapolation from living populations to ancient ancestral displacements must also be faced. For example, since Native American populations have almost exclusively type O blood, were their ancestors, who populated the Americas, also exclusively type O? Can genetic drift within an extremely small founder group explain this phenomenon? Type O blood confers a certain immunity to syphilis, which seems to be indigenous to the Americas and absent in the Old World before 1492. Did early immigrants without type O immunity die out before a sufficiently large New World population had developed to preserve non-O blood types? There may never be a definitive answer to these questions; the process of debate may be...
(The entire section is 1914 words.)