The Sports Gene: Inside the Science of Extraordinary Athletic Performance

by David Epstein

  As Jones pointed out, it would be blind and silly to ignore the importance of access to equipment and coaching. But this is a book about genetics and athleticism, and it would be just as blind to ignore the conspicuously thorough dominance of people with particular geographic ancestry in certain sports that are globally contested and have few barriers to entry. Namely, of course, that the athletes who are the fleetest of foot, in both short and long distances, are black.

  9

  We Are All Black (Sort Of)

  Race and Genetic Diversity

  You could carry a bag of blood onto an airplane in 1986. So the handoff that would help alter scientists’ understanding of race and human ancestry took place at John F. Kennedy International Airport, in a rugged nook of Queens, New York.

  Two colleagues of Yale geneticist Kenneth Kidd were traveling back from Africa with connecting flights at JFK, so he met them to collect the blood samples taken from the Biaka, a people from the Central African Republic, and the Mbuti, a people from the Democratic Republic of the Congo.

  Growing up in Taft, California, the son of a gas station manager, Kidd had been fascinated by genetics since he was a twelve-year-old puttering around in the garden, marveling at what happened when he cross-bred different color irises. As an adult, he graduated to studying human DNA. Even before that handoff at JFK, Kidd had an inkling of what he would find.

  At a scientific symposium in Italy in 1971 dedicated to the one hundredth anniversary of Darwin’s Descent of Man, Kidd had presented data showing that some African populations have more variations—different possible spellings of the same gene or area of the genome—in their DNA than populations from East Asia or Europe. At the time, many scientists contended that Africans, East Asians, and Europeans had all reached the Homo sapiens stage independently; that Homo erectus—the precursor to modern man—had evolved separately on each continent to become the distinct ethnic variations that we see today.

  Over the next two decades, Kidd filled his lab with the DNA of native populations spanning the globe. The Masai of northern Tanzania, the Druze of Israel, the Khanty of Siberia, the Cheyenne Native Americans of Oklahoma, Danes, Finns, Japanese, Koreans—all in translucent plastic containers color-coded by continent. Kidd collected some of the samples himself. Others, like DNA from the Hausa people of Nigeria, came from a Nigerian physician who was trying to figure out why women of certain ethnicities in southwest Nigeria give birth to twins at a higher frequency than women anywhere else on the planet.

  Part of Kidd’s goal was to categorize genetic variation around the world by looking at corresponding stretches of DNA in many different populations and examining how they differ. Every time he zoomed in on a portion of the double helix, a particular pattern held: more variation in the populations from Africa. For any piece of text in the DNA recipe book, there were almost always more possible spellings and phrasings in African populations than anywhere else in the world. In many areas of the genome, there was more genetic variation among Africans from a single native population than among people from different continents outside of Africa. On one particular stretch of DNA, Kidd observed more variation in one population of African Pygmies than in the entire rest of the world combined.

  With geneticist Sarah Tishkoff, Kidd drew a family tree to represent everyone on earth. While African populations fanned out to form the bulk of the tree, all the European populations were clustered on tiny branches on the fringes. “From that genetic point of view,” Kidd says, “I like to say that all Europeans look alike.” This is because nearly the entirety of human genetic information was contained in Africa not so very long ago.

  Kidd’s work, along with that of other geneticists, archaeologists, and paleontologists, supports the “recent African origin” model—that essentially every modern human outside of Africa can trace his or her ancestry to a single population that resided in sub-Saharan East Africa as recently as ninety thousand years ago. According to estimates made from mitochondrial DNA—and the rate at which changes to it occur—the intrepid band of our ancestors who ventured out from Africa en route to populating the rest of the world might have consisted of just a few hundred people.

  Humans split from our common ancestor with chimpanzees five or so million years ago. So relative to that time span, people have been outside of Africa for less—much less—than the equivalent of a two-minute drill in a football game. Because that band of our ancestors left not so very long ago in evolutionary terms, and took only a tiny fraction of the population along, they left behind most of humanity’s genetic diversity. For millions of years, DNA changes had accumulated—both randomly and by natural selection—in the genomes of our ancestors inside Africa. But with only ninety thousand years for unique changes to occur outside of Africa, there simply hasn’t been as much action in many stretches of the genome. People outside of Africa are descendants of genetic subsets of a group that was itself just a subset in Africa in the recent past.* Each time modern humans expanded to a new region of the globe, it appears that the pioneering emigrants were small in number and carried just a fraction of the genetic variation of their home en route to founding new populations. Data from around the world shows that the genetic diversity of native populations generally decreases the farther the population is along the human migratory path from East Africa, with populations native to the Americas tending to have the least genetic diversity.

  This has momentous implications for classifying people according to their skin color. In some cases, the fact of an individual’s black skin might indicate very little specific knowledge about his genome other than that he has genes that code for the dark skin that protects against equatorial sunlight. One African man’s genome potentially contains more differences from his black African neighbor’s than does Jeremy Lin’s genome from Lionel Messi’s.

  There might also be implications for sports. Kidd suggests that for any skill that has a genetic component, theoretically, both the most and least athletically gifted individuals in the world might be African or of recent African descent, like African Americans or Afro-Caribbeans. Both the fastest and slowest person might be African. Both the highest and lowest jumper might be African. In athletic competition, of course, we seek to identify only the fastest runners and highest jumpers. “One can certainly find individual genes where there’s more variation outside of Africa,” Kidd says, “but the general picture is that there’s more variation in Africa. . . . So you would expect out at the extremes there will be a greater proportion of people.”

  That said, there are clearly also average differences between populations, which is why Kidd does not recommend scouting for the next Olympic sprinter or NBA All-Star amid the staggering genetic diversity of African Pygmies. “There are certain anatomical features of the Pygmies that would intervene,” Kidd says, referring to their extremely short stature. “But you might find the best basketball players in some of those populations in Africa where height and coordination are on average very high, and where you have a lot of other genetic variation within that group.”

  Kidd is suggesting that certain Africans, or people of recent African ancestry, do have a genetic advantage in sports performance at the upper end of athleticism. But because he is not professing an average genetic advantage, Kidd’s supposition is intellectually palatable and has been touted as such both by scientists and in the press.

  •

  In the New Haven, Connecticut, lab that Kidd shares with his wife, Yale geneticist Judith Kidd, are the stainless steel refrigerators and garbage-bin-size liquid nitrogen containers that preserve the world’s DNA, all neatly color-coded. The Yoruba people from Nigeria are there in their translucent yellow plastic box, the Han Chinese in a green box, and, in a purple box, Ashkenazi Jews. If Kidd had my DNA, it would be in the purple box.

  In 2010, I had a portion of my genome analyzed by a private company that accurately traced my recent ancestry to eastern Europe and informed me t
hat I carry a mutation on one copy of my HEXA gene. If I procreate with a woman who also carries the same mutation on one of her HEXA genes, each of our children would have a one-in-four chance of receiving two mutant versions of the HEXA gene and having Tay-Sachs disease, a nervous system disorder that results in death by age four. The HEXA mutation is uncommon throughout most of the world, but around one in every thirty Jews with Polish or Russian ancestors (like me) are carriers. The HEXA mutation is one among a batch of DNA signatures that make the people in Kidd’s purple plastic box identifiable by their genes. Every one of the colorful boxes contains the DNA of populations with their own distinct genetic profiles.

  “This is a genetic locus [a location on the genome] that affects how well you degrade Tylenol,” Kidd says, through his handlebar mustache, as he clicks on a desktop file to open a study he coauthored. “There are certain mutations on this gene [CYP2E1] that cause acetaminophen poisoning of an individual.” A rainbow-colored diagram appears on Kidd’s monitor.

  In this study, as in numerous others he has conducted, Kidd documented how common particular DNA spellings of sections of a gene are in fifty native populations from around the world. As expected, all sixteen of the spelling variations of CYP2E1 that Kidd examined—each represented by a different color—can be found in people in Africa, as can a number of other DNA spelling combinations that are found nowhere else in the world. As the populations get farther from East Africa, through southwest Asia, Europe, northeast Siberia, Pacific Islands, East Asia, and the Americas, more and more of the colors drop out.

  “You see, in Africa you have the lavender, the magenta, the yellow, the black, whatever,” Kidd explains. “But when you get to Europe almost everybody is going to have at least one copy of the green one.” Among the Nasioi people, who are confined to the island of Bougainville in the Pacific Ocean near Papua New Guinea, every single member has the “green” DNA sequence in the CYP2E1 gene. “There are also Africans who have two copies of the green, so at that particular location [on the genome], one in a hundred Africans will be more similar to a European than another African,” Kidd says. “But overall they’re going to be very different from a European.” Not only because they have unique spellings in their genetic code, but also because the frequency of gene variations is different in different populations. By looking at just one segment of one single gene, Kidd can start the process of homing in on a person’s geographic and ethnic ancestry.

  As ancestral humans spread across the world and became separated by all manner of obstacles—mountains, deserts, oceans, social affiliations, and later national boundaries—populations developed their own DNA signatures. For nearly our entire history, people lived, married, and procreated predominantly where they were born. As pioneers set up civilizations in new locales, gene variants became more or less common in populations both by random chance, or “genetic drift,” as well as by natural selection when a version of a gene helped humans survive or reproduce in a new environment.

  The gene variant that allows some adults to digest lactose, the sugar in milk, is one example. The general rule for mammals is that the lactase enzyme is shut down after the weaning period, and milk can no longer be fully digested. That held true for essentially all humans just nine thousand years ago, before the domestication of cattle. Once humans kept dairy cows, though, any adult who could digest lactose was at a reproductive advantage, so gene variants for lactose tolerance spread like brushfire through societies that relied on dairy farming to thrive during winter, like those in northern Europe. Almost all present-day Danes and Swedes can digest lactose, but in populations in East Asia and West Africa, where cattle domestication is more recent or nonexistent, adult lactose intolerance is still the norm. Comedian Chris Rock famously joked that lactose intolerance is a luxury of wealthy societies: “You think anybody in Rwanda’s got a f——g lactose intolerance?!” Rock asked in one of his routines. In fact, most people in Rwanda are lactose intolerant.

  In an example particularly relevant to sports, about 10 percent of people with European ancestry have two copies of a gene variant that allows them to dope with impunity. The most common sports urine test that probes for illicit testosterone doping analyzes the ratio of testosterone to another hormone called epitestosterone—the “T/E ratio.” A normal ratio is one-to-one. Injecting synthetic testosterone upsets the ratio by pushing the T higher than the E, and drug testers consider a ratio above four-to-one to signify possible cheating. But carriers of two copies of a particular version of the UGT2B17 gene pass the test no matter what. The gene is involved in testosterone excretion and one version of it causes the T/E ratio to remain normal no matter how much testosterone one injects. So 10 percent of European athletes can cheat and still have no chance of failing the most common drug test. And the get-out-of-drug-testing-free gene is more rule than exception in other parts of the world, like East Asia. Two thirds of Koreans have the genes that confer immunity to T/E ratio testing.

  Despite our differences, because all humans have common ancestry that is not so distant in the past, we are exceedingly similar, more similar across the entire genome than chimpanzees are to one another. At the DNA level, of the three billion letters in the recipe book, humans are generally about 99 to 99.5 percent the same. In a sense, you probably knew that intuitively. If you had to build two human beings from scratch, no matter where in the world they were from, most of the instructions would be identical: two eyes, ten fingers and toes, a liver and two kidneys, all the same bones and brain chemicals. For that matter, just about every page would be the same for a human and a chimp, as we are 95 percent similar to chimps at the DNA level. But it is a mistake to take all that to mean that the differences are unimportant.

  At least 15 million letters of the DNA code differ on average between individuals, and the actual length of people’s genomic recipe book can differ by millions of letters as well. It is plenty enough difference to cause all the variation we see in the world. In 2007, as genome sequencing became faster and cheaper, Science, one of the two most prestigious scientific journals in the world, named as its breakthrough of the year the revelation of “how truly different we are from one another” at the genetic level. As genome sequencing has become cheaper still, that point has only been amplified. Wherever humans have set up civilizations, they have rapidly differentiated themselves.

  Though natives have inhabited Iceland for just a single millennium, the company deCODE Genetics showed that it could identify which of eleven regions of Iceland a resident’s grandparents hailed from using just forty areas along the genome. In 2008, scientists looking at much larger swaths of DNA pinpointed the geographic ancestry of nearly all of a sample of three thousand Europeans to within a few hundred miles. And, to a degree, DNA can identify the construct we call “race” as well.

  A 2002 study published by a team of researchers (including Kidd) in Science directed a computer to peruse 377 spots on the genomes of 1,056 people from around the world and then automatically separate the people into groups based on genetic differences. The groups that the computer delineated corresponded with the world’s major geographic regions: Africa, Europe, Asia, Oceania, and the Americas. A subsequent Stanford-led study asked 3,636 Americans to self-identify as either white, African American, East Asian, or Hispanic, and found that the self-identification matched a blind DNA identification in 3,631 cases. “This shows that people’s self-identified race/ethnicity is a nearly perfect indicator of their genetic background,” geneticist Neil Risch said in a press release issued by the Stanford University School of Medicine.*

  Skin color, which is primarily determined by latitude, can be an imprecise marker of geographical ancestry, as there are spectrums of skin color on each continent. But geography and ethnic affiliation have most certainly left a trail of genetic crumbs.

  In some areas of medicine, like pharmacogenetics—the study of how and why people with different genes respond differently to the same drugs—
skin color is already being used as a proxy, albeit often a crude one, for underlying genetic information, and medical researchers now recognize the importance of testing the efficacy of drugs separately on different ethnic groups.

  In 2004, Kidd and Tishkoff wrote that the main genetic and geographic clusters of people do “correlate with the common concept of ‘races,’” but added that if every population on earth were included, the genetic differences would look more like a continuous spectrum as opposed to a collection of discrete groups.

  In 2009, Tishkoff and an international team published a landmark study that characterized the genetic backgrounds of African Americans. They found that adults who identify as African American are highly genetically diverse on the whole, with ancestry ranging from 1 percent to 99 percent West African. African Americans are particularly diverse in the amount of European ancestry they have in their DNA. But almost all African Americans were found to have African X chromosomes, consistent with the idea that the mothers of African Americans have historically been of very recent African ancestry, while fathers were sometimes African and sometimes European. The African Americans studied were from Baltimore, Chicago, Pittsburgh, and North Carolina, and the African components of their genetic ancestry showed “little genetic differentiation,” according to Tishkoff, and were similar to one another and often to the genetic profiles of West African people like the Igbo and Yoruba of Nigeria; not a surprise, as the Igbo and Yoruba show up frequently in records of the slave trade as Africans who were wrenched from their homes and taken to the Caribbean and the United States.*