When I started my first academic job in 2003, I bet my career on the idea that the history of mixture of West Africans and Europeans in the Americas would make it possible to find risk factors that contribute to health disparities for diseases like prostate cancer, which occurs at about a rate 1.7 times higher in African Americans than in European Americans. This particular disparity had not been possible to explain based on dietary and environmental differences across populations, suggesting that genetic factors might play a role.
African Americans today derive about 80 percent of their ancestry from enslaved Africans brought to North America between the sixteenth and nineteenth centuries. In a large group of African Americans, the proportion of African ancestry at any one location in the genome is expected to be close to the average (defining the proportion of African ancestry as the fraction of ancestors that were in West Africa before around five hundred years ago). However, if there are risk factors for prostate cancer that occur at higher frequency in West Africans than in Europeans, then African Americans with prostate cancer are expected to have inherited more African ancestry than the average in the vicinity of these genetic variations. This idea can be used to pinpoint disease genes.
To make such studies possible, I set up a molecular biology laboratory to identify mutations that differed in frequency between West Africans and Europeans. My colleagues and I developed methods that used information from these mutations to identify where in the genome people harbor segments of DNA derived from their West African and European ancestors. To prove that these ideas worked in practice, we applied them to many traits, including prostate cancer, uterine fibroids, late-stage kidney disease, multiple sclerosis, low white blood cell count, and type 2 diabetes.
In 2006, my colleagues and I applied our methods to 1,597 African American men with prostate cancer, and found that in one region of the genome, they had about 2.8 percent more African ancestry than the average in the rest of their genomes. The odds of seeing a rise in African ancestry this large by accident were about ten million to one. When we looked in more detail, we found that this region contained at least seven independent risk factors for prostate cancer, all more common in West Africans than in Europeans. Our findings could account entirely for the higher rate of prostate cancer in African Americans than in European Americans. We could conclude this because African Americans who happen to have entirely European ancestry in this small section of their genomes had about the same risk for prostate cancer as random European Americans.
In 2008, I gave a talk about my work on prostate cancer to a conference on health disparities across ethnic groups in the United States. In my talk, I tried to communicate my excitement about the scientific approach and my conviction that it could help to find genetic risk factors for other diseases. Afterward, though, I was angrily questioned by an anthropologist in the audience, who believed that by studying “West African” or “European” segments of DNA to understand biological differences between groups, I was flirting with racism. Her questions were seconded by several others, and I encountered similar responses at other meetings.
A legal ethicist who heard me talk on a similar theme suggested that I might want to refer to the populations from which African Americans descend as “cluster A” and “cluster B.” But I replied that it would be dishonest to disguise the model of history that was driving this work. Every feature of the data I looked at suggested that this model was a scientifically meaningful one, providing accurate estimates of where in the genome people harbor segments of DNA from ancestors who lived in West Africa or in Europe in the last twenty generations, prior to the mixture caused by colonialism and the slave trade. It was also clear that the approach was identifying real risk factors for disease that differ in frequency across populations, leading to discoveries with the potential to improve health.
Far from being extremists, my questioners were articulating a mainstream view about the danger of work exploring biological differences among human populations. In 1942, the anthropologist Ashley Montagu wrote "Man’s Most Dangerous Myth: The Fallacy of Race", arguing that race is a social concept and has no biological reality, and setting the tone for how anthropologists and many biologists have discussed this issue ever since.
A classic example often cited is the inconsistent definition of “black.” In the United States, people tend to be called “black” if they have sub-Saharan African ancestry—even if it is a small fraction and even if their skin color is very light. In Great Britain, “black” tends to mean anyone with sub-Saharan African ancestry who also has dark skin. In Brazil, the definition is different yet again: a person is only “black” if he or she is entirely African in ancestry. If “black” has so many inconsistent definitions, how can there be any biological meaning to “race”?
In this way, through the collaboration of anthropologists and geneticists, a consensus was established that there are no differences among human populations that are large enough to support the concept of “biological race.” Lewontin’s results made it clear that for the great majority of traits, human populations overlap to such a degree that it is impossible to identify a single biological trait that distinguishes people in any two groups, which is intuitively what some people think of when they conceive of “biological race.”
But this consensus view of many anthropologists and geneticists has morphed, seemingly without questioning, into an orthodoxy that the biological differences among human populations are so modest that they should in practice be ignored—and moreover, because the issues are so fraught, that study of biological differences among populations should be avoided if at all possible. It should come as no surprise, then, that some anthropologists and sociologists see genetic research into differences across populations, even if done in a well-intentioned way, as problematic.
The concern is so acute that the political scientist Jacqueline Stevens has even suggested that research and even emails discussing biological differences across populations should be banned, and that the United States “should issue a regulation prohibiting its staff or grantee from publishing in any form - including internal documents and citations to other studies - claims about genetics associated with variables of race, ethnicity, nationality, or any other category of population that is observed or imagined as heritable."
The anthropologist Duana Fullwiley has written that the development of what she calls “admixture technology” and the language of “ancestry” that geneticists like me have adopted is a reversion to traditional ideas of biological race. She has pointed out that in the United States, the “ancestry” terms that we use map relatively closely to traditional racial categories, and her view is that the population genetics community has invented a set of euphemisms to discuss topics that had become taboo. The belief that we have embraced euphemisms is also shared by some on the other side of the political spectrum.
At a 2010 meeting I attended at Cold Spring Harbor Laboratory, the journalist Nicholas Wade described his resentment of the population genetics community’s “ancestry” terminology, asserting that “race is a perfectly good English word.” But ancestry is not a euphemism, nor is it synonymous with “race.” Instead, the term is born of an urgent need to come up with a precise language to discuss genetic differences among people at a time when scientific developments have finally provided the tools to detect them. It is now undeniable that there are nontrivial average genetic differences across populations in multiple traits, and the race vocabulary is too ill-defined and too loaded with historical baggage to be helpful.
I have deep sympathy for the concern that genetic discoveries about differences among populations may be misused to justify racism. But it is precisely because of this sympathy that I am worried that people who deny the possibility of substantial biological differences among populations across a range of traits are digging themselves into an indefensible position, one that will not survive the onslaught of science.
In the last couple of decades, most population geneticists have sought to avoid contradicting the orthodoxy. When asked about the possibility of biological differences among human populations, we have tended to obfuscate, making mathematical statements in the spirit of Richard Lewontin about the average difference between individuals from within any one population being around six times greater than the average difference between populations. But this carefully worded formulation is deliberately masking the possibility of substantial average differences in biological traits across populations.
