In his new book, A Troublesome Inheritance: Genes, Race, and Human History, science writer Nicholas Wade claims that race is real—that Darwinian natural selection has resulted in a number of biologically separate human populations characterized by distinct, genetically determined social behaviors. He asserts that many of these differences have emerged over the last 10,000 years and that they explain much of human history. He writes that recent science has “established that human evolution has been recent, copious, and regional” and uses this framework to account for regional variations in economic power and cultural pursuits.

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.

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.

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.

So is Wade right? Are there human races? Is the variation seen between different cultures and locations best explained by genetic differences between human populations? And have anthropologists been turning a blind eye to the evidence in front of them?

Early reviews of Wade’s book show a familiar division: Anthropologists mostly take a critical view, whereas psychologists and economists generally like the book. Agustín Fuentes, a zoologist and anthropologist, and Jonathan Marks, a geneticist trained in anthropology, are among the more negative; Bell Curve coauthor Murray and famed geneticist James Watson, a supporter of the biological race concept, land on the positive side. The favorable reviews almost invariably echo one of Wade’s key themes: Disbelief in the existence of race results from biased science driven by a left-leaning political agenda. Wade suggests that “any researcher who even discusses issues politically offensive to the left runs the risk of antagonizing the professional colleagues who must approve his requests for government funds and review his articles. . . The result is that researchers at present routinely ignore the biology of race.”

As soon as it appeared, Wade’s book touched off a firestorm of controversy—as he surely knew it would. It’s the latest in a series of dispatches concerning human variation, whose authors in recent decades have starkly divided into two camps, one centered in anthropology and the other in psychology, political science, and economics. Wade is in the latter camp. The Bell Curve: Intelligence and Class Structure in American Life, a widely read text by psychologist Richard Herrnstein and political scientist Charles Murray in 1994, proclaimed intractable human differences in ability between races; the authors based their views on disputed work published by Canadian psychologist J. Philippe Rushton in the 1980s and early 1990s. Meanwhile, anthropologists had developed a divergent concept of human variation, reaching the collective conclusion that the human species is not compartmentalized in races or subspecies (interchangeable terms in zoology). In 1998 the American Anthropological Association adopted its Statement on Race asserting that the best available research shows race to be a social construct that is biologically invalid.

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.

Throughout A Troublesome Inheritance, Wade frames his argument with a review of human evolution from a chimplike ancestor. Unfortunately, his depictions of evolution and his characterization of our hunter-gatherers ancestors are glib and inconsistent.

Wade claims that both chimpanzees and humans “inherited a genetic template” for social behavior from their common ancestor and asks why humans “should ever have lost the genetic template for . . . social behaviors.” But it has not been demonstrated that chimpanzee social behaviors differentiate because of genetics.

Chimpanzee subspecies are very different from each other genetically. In 1999 Henrik Kaessmann, Victor Wiebe, and Svante Pääbo reported in Science that “comparison to humans shows the diversity of chimpanzee sequences to be almost four times as high . . . as the corresponding values of humans.” That same year, Richard Warangham, Jane Goodall, and their colleagues published a Nature paper characterizing a great diversity in chimpanzee culture, including 39 distinct behavioral patterns, that could not be sorted out on the basis of subspecies and that were observed to be highly variable within subspecies. In short, chimp genetic variation has not been shown to correlate with cultural variation. Unlike humans, chimpanzees do have true races, but racial differences just don’t explain cultural differences among chimps.

Elsewhere, Wade refers problematically to the “nomadic life of hunter- gatherer bands.” Making no reference to actual studies, he uses a broad brush to paint a hunter-gatherer culture unsubstantiated by any recognizable ethnography. His descriptions of how hunter-gatherers deal with social transgressions and interpersonal violence instead recall the writings of 19th century armchair anthropologists. Wade does not appear familiar with the primary and current literature on foragers, and he makes the additional mistake of accepting psychologist Steven Pinker’s mischaracterization of the data on the high rate of violence among hunter-gatherers. The archaeological record shows periods when violence rates spiked in some ancient groups, but skeletal remains from ancient foragers are rare and so the data are sparse. We who study living hunter-gatherers generally have the impression that they are violence averse. There is a good chance that changes in levels of violence in past human societies have been multidirectional and complex.

Pressing his thesis on the links between genes and behavior, Wade states that the transition to agriculture meant that “the aggressive and independent nature of hunter-gatherers, accustomed to trusting only their close kin, had to yield to a more sociable temperament and the ability to interact peaceably with larger number of people.” Wade seems to have invented a form of hunter-gatherer and characterized it to fit his expectations of (inconveniently unproven) genetically determined social behavior. Having lived on the outskirts of peaceful horticultural settlements with very peaceful hunter-gatherers in Central Africa during the first Gulf War, I have quite different impressions of the alleged evolution toward peacefulness. My anecdotal experience doesn’t dismantle Wade’s argument, but it points to a historical complexity that he overlooks.

There is a more straightforward explanation for behavioral variation among humans, much more likely accurate than the one Wade proposes. This explanation is embedded in current anthropological thinking and fits better with observations of what makes humans unique among kindred species.

It ties back to individual human development. Our species pays a huge evolutionary cost for its extended childhood. Unlike our ape relatives, we are born and remain for years nearly helpless and at risk. Birth itself is costly and dangerous because of our large brain. These things are linked. A typical human adult is imbued with human qualities by virtue of an extended period of learning and enculturation during which that big brain is shaped by its environment. Were our children born with more genetic programming for social behavior, the brain could potentially be smaller, growing up could be faster, the emergence of appropriate behavior more reliable, and reproductive output higher.

Our large brains have a high metabolic cost as well, and accounting for this cost has been central to many recent theories of human evolution, including Richard Wrangham and his colleagues’ cooking hypothesis and Leslie Aiello and Peter Wheeler’s expensive-tissue hypothesis, which together explain where the energy for growing and maintaining large brains comes from.

Our relatively slow reproductive rate and the extended demands of child rearing are thought to be compensated for by the evolution of reproductive senescence (menopause). “The Grandmother Hypothesis,” as it’s sometimes called, posits that older women forgo their own reproduction in favor of providing critical investment in raising grandchildren. These contemporary interpretations of human evolution do not exclude genetic change; large brains, language, menopause, and other unique human features clearly have genetic underpinnings. But the features themselves seem linked to a system of developing appropriate social behavior as part of human cultural adaptability and are not expected to manifest as distinct fine-tuned genetic adaptations in different races.

Most likely, a key human trait involved is an adaptability to diverse contexts through learning, which is in turn facilitated by these costly features. Hence, an excellent explanation for variation across human populations is culture, not genes.

Learning and enculturation explain most human behavioral variation. This is a basic tenet of modern anthropology. Perhaps the best evidence is the simple fact that children adopted as infants across vast cultural boundaries do not carry their parents’ social behavior with them. More broadly, sudden large-scale changes in national or regional economy, such as the uniting of East and West in Germany, produce rapid change in IQ measures and social behavior. Oddly, Wade acknowledges that these things happen within a race, or at least one race (Caucasian), but insists that when the same traits vary across races they can be accounted for only by evolutionary genetic change.

Ultimately, Wade claims that modern anthropology ignores key scientific information for political reasons, yet his own arguments are only thinly supported by data, and much of the data he does reference isn’t rigorous. To his credit, he refutes certain racist notions associated with the idea of genetic determinism, and he speaks against social Darwinism and similar concepts. But if that verbiage were excised, his book would fit comfortably in the early to mid-20th century literature on race and human variation. A Troublesome Inheritance is itself troubling, not for its politics but for its science. Its arguments are only mildly amended versions of arguments discarded decades ago by those who methodically and systematically study human behavioral variation across cultures.

Greg Laden is a biological anthropologist who has worked in the Democratic Republic of Congo and South Africa. He writes at Scienceblogs.com.