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BOOK REVIEW

A Troubling Tome

Greg Laden

Wade’s claim that races really do exist is based partly on genetic sampling of geographically distant populations. These samples appear to show clustering into distinct groups by gene variants, also known as alleles. But sampling geographically distant parts of a continuum and ignoring the regions between the samples can provide apparent clustering that does not actually prove the existence of discrete groups.

Biologists have long understood, based on numerous studies with animals and plants, that the primary underlying factor determining within-species genetic variation is simple geographic distance. Novel alleles emerge through mutation and spread locally, so the greater the geographic distance between genetic samples, the more different the samples will appear. Numerous studies over the past few decades have demonstrated the strong association between geographic distance and genetic difference in human populations. For instance, in 2005 the Human Genome Diversity project published a paper in the Proceedings of the National Academies of Science of the U.S.A. reporting “a linear relationship between genetic and geographic distance in a worldwide sample of human populations,” with notable but uncommon deviations explained by “admixture or extreme isolation.” This work also showed that the majority of genetic differences across human populations were independent for each gene’s alleles—that is, we do not see Homo sapiens divided into groups with each group defined by a characteristic set of genetic differences.

This lack of clear divisions undercuts two important assumptions at the core of Wade’s argument. First, there are very few, if any, natural genetic boundaries between groups of people. The appearance of clear distinctions is an artifact of people’s geographical movement—as colonists or slaves, for example—and presumably short-lived on evolutionary time scales. Second, it is not scientifically possible to classify people into a “race” on the basis of certain traits (usually physical appearance) and then use that classification to reliably predict other, less visible, genetic features.

Without boundaries or predictive value, race isn’t a valid biological concept. Human races may have existed in the past—just as there are subspecies of a number of different mammals, including chimpanzees—and they could exist in the future. Nonetheless, to this point the history of Homo sapiens has not led to a known emergence of distinct races. We evolved recently, spread quickly, and in many regions interacted readily. Race is a powerful and important social construct, and in that way it is very real, but it is not a biological useful concept for understanding human diversity.

Not surprisingly, then, many of the examples Wade uses to discuss the evolution of human traits are probably not linked to genetic changes at all. For example, he refers to research in Quebec showing that during the 19th and early 20th centuries the age of first reproduction among women declined from 26 to 22 years. Although it may be argued that this is a heritable trait, we see similar changes happening in other populations globally far too quickly to be explained by genetic change. Alternative explanations abound, ranging from shifting cultural norms to changing diet. Claiming a genetic cause requires evidence of the genes involved, but Wade produces none.

Similarly, IQ has changed rapidly in some populations and is known to fluctuate a great deal in response to economic conditions and other nongenetic factors; significant shifts can occur over a few generations, or even in a single one. Wade acknowledges this, and seems to accept that changes of well over 10 points in average IQ have occurred because of environmental factors among European populations. Still, he argues that differences in intellectual capacity between what he calls the three major races are innate, and that those differences can explain disparities between regions in economic and political success. (Further confusing things, he is inconsistent in assigning a number to the races he believes exists. He references the “three races” of sub-Saharan Africans, East Asians, and Caucasians, yet elsewhere adds a “fourth race, the natives of North and South America” and later brings in a fifth race, “the peoples of Australia and Papua New Guinea.”)

Wade writes that “a part of the world has grown steadily and vastly richer over the last 300 years. This is not an accident or luck, and a reasonable explanation is available in terms of human evolution. . . The explanation is that there has been an evolutionary change in human social behavior that has facilitated the new, posttribal social structure on which modern societies are based.” He catalogs “Jewish adaptations” as primary examples, referring for instance to rates of winning Nobel prizes. In making the argument that such adaptations are genetic, Wade intimates why no other group is like the Jews: “People are highly imitative, and if the Jewish advantage were purely cultural, such as hectoring mothers or a special devotion to education, there would be little to prevent others from copying it.” More likely, he concludes, “the adaptation of Jews to a special cognitive niche . . . represents a striking example of natural selection’s ability to change a human population in just a few centuries.”

In Wade’s (partial) defense, genes undoubtedly do underlie human behavior in countless ways. Yet, despite decades of searching, evidence of a simple relationship between genes and behavior has remained elusive. There simply is not an accepted list of alleles that account for behavioral variation. This data vacuum has caused those who firmly believe that such alleles exist to redefine how the genetics must work. Rather than expecting one or two genes to have a few variants that affect certain traits, it has become fashionable to say that thousands of genes each contribute minutely to surface variation in behavior. As Wade puts it, traits like intelligence “are controlled by a large number of different genes [with] alleles that individually make small contributions to the trait. So if just some of these alleles become a little more common . . . the trait will be significantly affected.” There may be something to that, but it is unsatisfying that the presumed phenomenon, having not been found, is still reputed to exist but in invisible form. Further, in asserting that a small change in the distribution of the presumed alleles will result in a significant effect, Wade presumes to be able to measure a phenomenon whose very existence is unsupported.








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