Who We Are and How We Got Here

by David Reich

  Wade is far from the only person who is convinced he knows the truth about the differences among populations. At the same 2010 meeting on “DNA, Genetics, and the History of Mankind” at which I first met Wade, I heard a rustling behind my shoulder and turned with a shock to see James Watson, who in 1953 codiscovered the structure of DNA. Watson had until a few years earlier been the director of the Cold Spring Harbor Laboratory at which the meeting was held. A century ago, the laboratory was the epicenter of the eugenics movement in the United States, keeping records on traits in many people to help guide selective breeding, and lobbying for legislation that was passed in many states to sterilize people considered to be defective and to combat a perceived degradation of the gene pool. It was ironic, then, that Watson was forced to retire as head of Cold Spring Harbor after being quoted in an interview with the British Sunday Times newspaper as having said that he was “inherently gloomy about the prospect of Africa,” adding that “[all] our social policies are based on the fact that their intelligence is the same as ours—whereas all the testing says not really.”44 (No genetic evidence for this claim exists.) When I saw Watson at Cold Spring Harbor, he leaned over and whispered to me and to the geneticist Beth Shapiro, who was sitting next to me, something to the effect of “When are you guys going to figure out why it is that you Jews are so much smarter than everyone else?” He then said that Jews and Indian Brahmins were both high achievers because of genetic advantages conferred by thousands of years of natural selection to be scholars. He went on to whisper that Indians in his experience were also servile, much like he thought they had been under British colonialism, and he speculated that this trait had come about because of selection under the caste system. He also talked about how East Asian students tended to be conformist, because of selection for conformity in ancient Chinese society.

  The pleasure Watson takes in challenging establishment views is legendary. His obstreperousness may have been important to his success as a scientist. But now as an eighty-two-year-old man, his intellectual rigor was gone, and what remained was a willingness to vent his gut impressions without subjecting them to any of the testing that characterized his scientific work on DNA.

  Writing now, I shudder to think of Watson, or of Wade, or their forebears, behind my shoulder. The history of science has revealed, again and again, the danger of trusting one’s instincts or of being led astray by one’s biases—of being too convinced that one knows the truth. From the errors of thinking that the sun revolves around the earth, that the human lineage separated from the great ape lineage tens of millions of years ago, and that the present-day human population structure is fifty thousand years old whereas in fact we know that it was forged through population mixtures largely over the last five thousand years—from all of these errors and more, we should take the cautionary lesson not to trust our gut instincts or the stereotyped expectations we find around us. If we can be confident of anything, it is that whatever differences we think we perceive, our expectations are most likely wrong. What makes Watson’s and Wade’s and Harpending’s statements racist is the way they jump from the observation that the academic community is denying the possibility of differences that are plausible, to a claim with no scientific evidence45 that they know what those differences are and also that the differences correspond to long-standing popular stereotypes—a conviction that is essentially guaranteed to be wrong.

  We truly have no idea right now what the nature or direction of genetically encoded differences among populations will be. An example is the extreme overrepresentation of people of West African ancestry among elite sprinters. All the male finalists in the Olympic hundred-meter race since 1980, even those from Europe and the Americas, had recent West African ancestry.46 The genetic hypothesis most often invoked to explain this is that there has been an upward shift in the average sprinting ability of people of West African ancestry due to natural selection. A small increase in the average might not sound like much, but it can make a big difference at the extremes of high ability—for example, a 0.8-standard-deviation increase in the average sprinting ability in West Africans would be expected to lead to a hundredfold enrichment in the proportion of people above the 99.9999999th percentile point in Europeans. But an alternative explanation that would predict the same magnitude of effect is that there is simply more variation in sprinting ability in people of West African ancestry—with more people of both very high and very low abilities.47 A wider spread of abilities around the same mean and a hundredfold enrichment in West Africans in the proportion of people above the 99.9999999th percentile point seen in Europeans is in fact exactly what is expected given the approximately 33 percent higher genetic diversity in West Africans than in Europeans.48 Whether or not this explains the dominance of West Africans in sprinting, for many biological traits—including cognitive ones—there is expected to be a higher proportion of sub-Saharan Africans with extreme genetically predicted abilities.

  So how should we prepare for the likelihood that in the coming years, genetic studies will show that behavioral or cognitive traits are influenced by genetic variation, and that these traits will differ on average across human populations, both with regard to their average and their variation within populations? Even if we do not yet know what those differences will be, we need to come up with a new way of thinking that can accommodate such differences, rather than deny categorically that differences can exist and so find ourselves caught without a strategy once they are found.

  It would be tempting, in the wake of the genome revolution, to settle on a new comforting platitude, invoking the history of repeated admixture in the human past as an argument for population differences being meaningless. But such a statement is wrongheaded, as if we were to randomly pick two people living in the world today, we would find that many of the population lineages contributing to them have been isolated from each other for long enough that there has been ample opportunity for substantial average biological differences to arise between them. The right way to deal with the inevitable discovery of substantial differences across populations is to realize that their existence should not affect the way we conduct ourselves. As a society we should commit to according everyone equal rights despite the differences that exist among individuals. If we aspire to treat all individuals with respect regardless of the extraordinary differences that exist among individuals within a population, it should not be so much more of an effort to accommodate the smaller but still significant average differences across populations.

  Beyond the imperative to give everyone equal respect, it is also important to keep in mind that there is a great diversity of human traits, including not just cognitive and behavioral traits, but also areas of athletic ability, skill with one’s hands, and capacity for social interaction and empathy. For most traits, the degree of variation among individuals is so large that any one person in any population can excel at any trait regardless of his or her population origin, even if particular populations have different average values due to a mixture of genetic and cultural influences. For most traits, hard work and the right environment are sufficient to allow someone with a lower genetically predicted performance at some task to excel compared to people with a higher genetically predicted performance. Because of the multidimensionality of human traits, the great variation that exists among individuals, and the extent to which hard work and upbringing can compensate for genetic endowment, the only sensible approach is to celebrate every person and every population as an extraordinary realization of our human genius and to give each person every chance to succeed, regardless of the particular average combination of genetic propensities he or she happens to display.

  For me, the natural response to the challenge is to learn from the example of the biological differences that exist between males and females. The differences between the sexes are in fact more profound than those that exist among human populations, reflecting more than a hundred million years of evolution and adaptation. Males and females differ by hu
ge tracts of genetic material—a Y chromosome that males have and that females don’t, and a second X chromosome that females have and males don’t. Most people accept that the biological differences between males and females are profound, and that they contribute to average differences in size and physical strength as well as in temperament and behavior, even if there are questions about the extent to which particular differences are also influenced by social expectations and upbringing (for example, many of the jobs in industry and the professions that women fill in great numbers today had few women in them a century ago). Today we aspire both to recognize that biological differences exist and to accord everyone the same freedoms and opportunities regardless of them. It is clear from the abiding average inequities that persist between women and men that fulfilling these aspirations is a challenge, and yet it is important to accommodate and even embrace the real differences that exist, while at the same time struggling to get to a better place.

  The real offense of racism, in the end, is to judge individuals by a supposed stereotype of their group—to ignore the fact that when applied to specific individuals, stereotypes are almost always misleading. Statements such as “You are black, you must be musical” or “You are Jewish, you must be smart” are unquestionably very harmful. Everyone is his or her own person with unique strengths and weaknesses, and should be treated as such. Suppose you are the coach of a track-and-field team, and a young person walks on and asks to try out for the hundred-meter race, in which people of West African ancestry are statistically highly overrepresented, suggesting the possibility that genetics may play a role. For a good coach, race is irrelevant. Testing the young person’s sprinting speed is simple—take him or her out to the track to run against the stopwatch. Most situations are like this.

  A New Basis for Identity

  The genome revolution is actually a far more effective force for coming to a new understanding of human difference and identity—for understanding our own personal place in the world around us—than for promoting old beliefs that more often than not are mistaken.

  To understand the power of the genome revolution for undermining old stereotypes about identity and building up a new basis for identity, consider how its finding of repeated mixture in human history has destroyed nearly every argument that used to be made for biologically based nationalism. The Nazi ideology of a “pure” Indo-European-speaking Aryan race with deep roots in Germany, traceable through artifacts of the Corded Ware culture, has been shattered by the finding that the people who used these artifacts came from a mass migration from the Russian steppe, a place that German nationalists would have despised as a source.49 The Hindutva ideology that there was no major contribution to Indian culture from migrants from outside South Asia is undermined by the fact that approximately half of the ancestry of Indians today is derived from multiple waves of mass migration from Iran and the Eurasian steppe within the last five thousand years.50 Similarly, the idea that the Tutsis in Rwanda and Burundi have ancestry from West Eurasian farmers that Hutus do not—an idea that has been incorporated into arguments for genocide51—is nonsense. We now know that nearly every group living today is the product of repeated population mixtures that have occurred over thousands and tens of thousands of years. Mixing is in human nature, and no one population is—or could be—“pure.”

  Nonscientists have already realized the potential of the genome revolution for forming new narratives. African Americans have been at the forefront of this movement. During the slave trade, Africans were uprooted and forcibly deprived of their culture, with the effect that within a few generations much of their ancestors’ religion, language, and traditions were gone. In 1976, Alex Haley’s novel Roots used literature to begin to reclaim lost roots by recounting the odyssey of the slave Kunta Kinte and his descendants.52 Following in this tradition, Harvard professor of literature Henry Louis Gates Jr. has capitalized on the potential of genetic studies to recover lost roots for African Americans. In his Faces of Americans television series and the Finding Your Roots series that followed it, he declares to the cellist Yo-Yo Ma, who is able to trace his ancestry back to thirteenth-century China, that Gates, as an African American, will never know how that feels, but he shows that genetics can provide richly informative insights even for African Americans with limited genealogical records.53

  A new industry, “personal ancestry testing,” has sprung up to capitalize on the potential of the genome revolution to form the basis for new narratives and to compare the genomes of consumers to others who have already been tested. The television programs that Gates has produced have been built around the idea of tracing the genealogies and DNA of celebrity guests, using the literary device of telling the personal stories of famous people to help viewers understand the power of genetic data to reveal features of their family’s past about which they could not otherwise have been aware. For example, the programs revealed unknown deep relationships between pairs of guests on the program (shared ancestors within the last few hundred years). They also used genetic tests to determine not only the continents on which people’s ancestors lived, but also the regions within continents.

  As a white person in the United States with its history of forcible deprivation of peoples of their roots, I feel that everyone—African Americans and Native Americans especially—has the right to try to use genetic data to help fill in missing pieces in his or her family history. Nevertheless, for those who assume that personal ancestry testing results have the authority of science, it is important to keep in mind that many of the results are easily misinterpreted and rarely include the warnings that scientists attach to tentative findings.

  Some of the best examples come from the industry that sprang up to provide genetic results to African Americans. One company is African Ancestry, which provides customers with information on the West African tribe and country in which their Y-chromosome or mitochondrial DNA type is most common. Such results are easy to overinterpret, as the frequencies of Y-chromosome and mitochondrial DNA types are too similar across West Africa to make exact determinations with confidence. As an example, consider a Y-chromosome type that is carried slightly more often in the Hausa ethnic group than in the neighboring Yoruba, Mende, Fulani, and Beni groups. When African Ancestry sends its report, it might state that an African American man has a Y-chromosome type that is most common in the Hausa.54 But it is quite possible and even likely that the true ancestor was not the Hausa, because there are many tribes in West Africa, and no one tribe contributed more than a modest fraction of the African ancestry of African Americans.55 And yet people who have taken these tests often return with the impression that they know their origin. The geneticist Rick Kittles, a population geneticist who is the cofounder of African Ancestry, described this feeling, asserting, “My female line goes back to northern Nigeria, the land of the Hausa tribe. I then went to Nigeria and talked to people and learned about the Hausa’s culture and tradition. That gave me a sense about who I am.”56 Whole-genome ancestry tests in theory have much more power than tests based on Y chromosomes and mitochondrial DNA. But at present, even whole-genome methods are not good enough to provide high-resolution information about where the ancestors of an African American person lived within Africa, in part because the databases of present-day populations in West Africa are not complete enough. Much more research needs to be done to make it possible to carry out studies like these with any reliability.

  For African Americans, another frustration may be that the cultural upheaval that occurred after African slaves arrived in North America has been so enormous that today there are few differences among African Americans with respect to the places in Africa from which their ancestors came. Africans from one part of the continent were traded around and mixed with those from another, with the result that within a few generations the great cultural diversity and variation of ancestry that existed among the first slaves were blurred to the point of unrecognizability. The nearly complete homogenization of African ancestry that
occurred was evident in an unpublished study I carried out in 2012 with Kasia Bryc, who analyzed genome-wide data from more than fifteen thousand African Americans from Chicago, New York, San Francisco, Mississippi, North Carolina, and the South Carolina Sea Islands, and tested if some African American populations were more closely related to particular West Africans than others, as might be expected based on the heterogeneous supply routes for U.S. slaves.57 It made sense to expect some differences. Of the four big slave ports, New Orleans was supplied mostly by French slave traders, whereas Baltimore, Savannah, and Charleston were supplied mostly by the British drawing from different points in Africa. But what we found is that the mixing of the West African ancestors of African Americans has been so thorough that we could not detect any differences in the African source populations for mainland populations. Only in the Sea Islands off South Carolina did we detect evidence of a particular connection to one place in Africa, in this case to people of the country of Sierra Leone, the place of origin of the language with an African grammar still spoken by Gullah Sea Islanders. It will take ancient DNA studies of first-generation enslaved Africans to actually trace roots to Africa.58

  The problem with the results sometimes provided by personal ancestry testing companies is not limited to African Americans. It is a more general pitfall that stems from the financial incentive that such companies have to provide people with what feel like meaningful findings. This is a problem even for the most rigorous of the companies. Between 2011 and 2015, the genetic testing company 23andMe provided customers with an estimate of their proportion of Neanderthal ancestry, allowing them to make a personal connection to the research showing that non-Africans derive around 2 percent of their genomes from Neanderthals.59 The measurement made by the test was highly inaccurate, however, since the true variation in Neanderthal proportion within most populations is only a few tenths of a percent, and the test reports variation of a few percentage points.60 Several people have told me excitedly that their 23andMe Neanderthal testing result put them in the top few percent of people in the world in Neanderthal ancestry, but because of the test’s inaccuracies, the probability that people who got such a high 23andMe Neanderthal reading really do have more than the average proportion of Neanderthal ancestry is only slightly greater than 50/50. I raised this problem to members of the 23andMe team and even highlighted the problems in a 2014 scientific paper.61 Later, 23andMe changed its report to no longer provide these statements. However, the company continues to provide its customers with a ranking of the number of Neanderthal-derived mutations they carry.62 This ranking, too, does not provide strong evidence that customers have inherited more Neanderthal DNA than their population average.