The Sports Gene: Inside the Science of Extraordinary Athletic Performance (15 page)

Stat-savvy general managers have no doubt noticed. Daryl Morey, the MIT-educated GM of the Houston Rockets, renowned for his Moneyball approach to basketball, has drafted several of the most superficially undersized players in the NBA. (Morey would not comment on whether the Rockets strategically targeted high wingspan-to-height-ratio players in the draft.) Three seasons ago, the Rockets used the shortest starting center in NBA history, Chuck Hayes, who is just 6'5½". Fortunately, his arms are 6'10".

The bottom line is that not only are NBA players outlandishly tall, they are also preposterously long, even relative to their stature. And when an NBA player does not have the height required to fit into his slot in the athletic body types universe, he nearly always has the arm span to make up for it. In the post–Big Bang of body types era, whether with height or reach, almost no player makes the NBA without a functional size that is typical for his position and often on the fringe of humanity. Only two players from a 2010–11 NBA roster with available official measurements have arms shorter than their height. One is J. J. Redick, the Milwaukee Bucks guard who is 6'4" with a 6'3¼" arm span, downright
Tyrannosaurus rex
-ian in the NBA.
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The other is now-retired Rockets center Yao Ming. But at a height just over 7'5", Yao, whose gargantuan parents were brought together for breeding purposes by the Chinese basketball federation, fit into his niche just fine.

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Repeatedly, studies of families and twins find the heritability of height to be about 80 percent. That means that 80 percent of the difference in height between people in the group that is being studied is attributable to genetics, and around 20 percent to the environment. (In nonindustrialized societies, the heritability of height is lower, as many citizens, like plants in poor soil, are prevented by nutritional deficiencies or infections from reaching their genetic height potential.) So if the tallest 5 percent of citizens in a given population are a foot taller than the shortest 5 percent, genetics will account for about ten inches of the disparity.

For much of the twentieth century, denizens of industrialized societies were growing taller at a rate of about one centimeter per decade. In the seventeenth century, the average Frenchman was 5'4", which is now the average for an American woman. The first generation of Japanese born to immigrant parents in America, known as the Nisei, famously towered over their parents.

In the 1960s, growth expert J. M. Tanner examined a set of identical twins that suggested the range of height variability caused by the environment. The identical boys were separated at birth, one brother raised in a nurturing household, and the other reared by a sadistic relative who kept him locked in a darkened room and made him plead for sips of water. In adulthood, the brother from the nurturing household was three inches taller than his identical twin, but many of their body proportions were similar. “The genetic control of shape is more rigorous than that of size,” Tanner wrote in
Fetus into Man
. The smaller brother was an abuse-shrunken version of the bigger brother.

Little is known about the actual genes that influence height, however, because the genetics of even outwardly simple traits tend to be very complicated. A 2010 study in
Nature Genetics
needed 3,925 subjects and 294,831 single nucleotide polymorphisms—spots of DNA where a single letter can vary between people—to account for just 45 percent of the variance in height between adults, and that’s the best
any study has done. Finding all the height genes will take much larger and more complex studies than scientists presumed a decade ago.

Though the genes are difficult to pinpoint, the genetically programmed nature of height is obvious from studies of identical twins. Due to distinct intrauterine conditions, identical twins are often
less
similar in birth size than fraternal twins. And yet, after birth, the smaller twin of an identical duo quickly catches up with the bigger twin and they will be nearly or exactly the same height as adults. Similarly, female gymnasts delay their growth spurt with furious training, but that does not diminish their ultimate adult height. The genetic programming is also evident in the rate at which children grow. In World Wars I and II, European children were exposed to brief periods of famine during which their growth ground almost to a halt. When food again became plentiful, their bodies put the growth pedal to the metal such that adult height was not curtailed. “The undernourished child slows down and waits for better times,” Tanner wrote. “All young animals have the capacity to do this. . . . Man did not evolve in the supermarket society of today.”

The permutations of size-determining interactions between nature and nurture are fathomless. Consider that children grow more quickly in spring and summer than in fall and winter, and that this is apparently due to sunlight signals that enter through the eyeballs, since the growth of totally blind children consists of similar fluctuations but are not synchronized with the seasons.

The height that inhabitants of urban societies gained over the twentieth century came principally from increased leg length. Legs got longer faster than torsos. In developing countries that have gaping nutritional and infection-prevention disparities between the middle class and poor, the difference in height between the comfortable and the afflicted is all in the legs.

Japan displayed a startling growth trend during its “economic miracle” period following World War II. From 1957 to 1977, the average height of a Japanese man increased by 1.7 inches, and of a woman by an inch. By 1980, the height of Japanese people in Japan had caught up
with the height of Japanese people in America. Amazingly, the entire height increase was accounted for by increased leg length. Modern Japanese people are still short compared with Europeans, but not as short as they once were. And they now have more similar proportions.

•

There are, however, certain body type differences that have persisted over time and that have attracted the interest of sports anthropometrists. Every study that has examined race differences in body types has documented a disparity between black and white people that remains whether they reside in Africa, Europe, or the Americas. For any given sitting height—that is, the height of one’s head when one is sitting in a chair—Africans or African Americans have longer legs than Europeans. For a sitting height of two feet, an African American boy will tend to have legs that are 2.4 inches longer than a European boy’s. Legs make up a greater proportion of the body in an individual of recent African origin.
*
And this holds for elite athletes.

Studies of Olympic athletes are uniformly consistent in finding that Africans and African Americans and African Canadians and Afro-Caribbeans have a more “linear” build than their competitors of Asian and European descent. That is, they tend to have longer legs and more narrow pelvic breadth.

In their summary of the measurements of 1,265 Olympians from the 1968 Olympics in Mexico City, the scientists state that the successful body types within a sport are much more similar than body types between sports, regardless of ethnicity, but that “the most persistent of these differences” within sports are the narrow hip breadths and longer arms and legs of athletes with recent African ancestry. “They appear in virtually all the events,” the researchers write.

Modern scientists who have measured athletes mention in their writing, sometimes reluctantly, that these body type differences influence athletic performance. The scientists are often careful to point out that a particular body type is not
better
overall, but that it may fit more readily into one sports niche than another. “This pattern may, in part, explain the tendency for the linear and relatively long-limbed east Africans to excel in endurance events while the short-limbed eastern Europeans and Asians have a long history of success in weight lifting and gymnastics,” write Norton and Olds, the Big Bang of body types gurus, in their textbook
Anthropometrica
.

The limb-length difference manifests in NBA data as well.
*
In NBA predraft measurements for active players, the average white American NBA player was 6'7½" with a wingspan of 6'10". The average African American NBA player was 6'5½" with a 6'11" wingspan; shorter but longer. Both white and black players in the NBA have wingspan-to-height ratios much greater than the population average, but there’s a sizable gap between white and black players. The average ratio for a white American NBA player is 1.035, and for an African American NBA player 1.071. Still, there is wide variation among players within a given ethnicity. Two white players, Coby Karl (height: 6'3½", wingspan: 6'11") and Cole Aldrich (height: 6'9", wingspan: 7'4¾"), for example, have wingspan-to-height ratios approaching 1.10, but they are significant outliers compared with the other white players in the NBA. No other white players are even close, whereas a number of black players have larger ratios. When I showed this data to a scientist who studies athletes’ bodies, he responded: “So maybe it’s not so much that white men can’t jump. White men just can’t reach high.”
*

In a sense, this is last millennium’s news to scientists who have
been studying body forms. In 1877, American zoologist Joel Asaph Allen published a seminal paper in which he noted that the extremities of animals get longer and thinner as one travels closer to the equator. African elephants can be distinguished from Asian elephants by their sail-like floppy ears. This is because the ears, like your skin, act as a radiator to release heat. The greater the surface area of the radiator compared with its volume, the more quickly heat is released. The African elephants, having evolved closer to the equator, have developed larger ears for cooling purposes. “Allen’s rule,” that animals from warmer climates tend to have longer limbs, has been extended to humans by a veritable filing cabinet full of studies.

A 1998 analysis of hundreds of studies of native populations from around the world found that the higher the average annual temperature of a geographic region, the proportionally longer the legs of the people whose ancestors had historically resided there. Men and women from dozens of native populations on every inhabited continent were included, and when it came to leg length, they grouped by geography. Low-latitude Africans and Australian Aborigines had the proportionally longest legs and shortest torsos. So this is not strictly about ethnicity so much as geography. Or latitude and climate, to be more precise. Africans with ancestry in southern regions of the continent, farther from the equator, do not necessarily have especially long limbs. But whether an African person in the study was from a population in Nigeria or from a genetically and physically distinct population in Ethiopia, so long as he was from low latitude his legs were likely longer than those of a height-matched European. And certainly longer than those of an Inuit from northern Canada, as Inuit tend to be short and stocky with compact limbs and a wide pelvis.
*

In the nineteenth century, Allen surmised that the long limbs of low-latitude animals were a
direct
result of a warm climate. In other
words, he guessed that if a baby African elephant were adopted by Asian elephant parents and raised at high latitude in Asia, it would have the same smallish ears as Asian elephants. On that point, he was mistaken. Comparisons of human descendants of equatorial Africans and of Europeans who now live in the same country, like England or the United States, show that the limb differences remain. The effect of climate on extremities is therefore primarily through genetic selection over generations. Ancestral humans with shorter limbs had a greater chance of surviving and reproducing in cold northern latitudes because they retained more heat.

In 2010, a racially diverse research team from Duke and Howard universities confronted the issue of body types as it pertains to ancestry and sports performance. The scientists did a backbend to avoid racial stereotyping. “Our study does not advance the notion of race,” they wrote. In a press release accompanying the study, Edward Jones, a black member of the research team, emphasized that access to sports facilities is critical for athletic development and that while growing up in South Carolina he was discouraged from swimming. Nonetheless, the researchers reported that, compared with white adults of a given height, black adults have a center of mass—approximately the belly button—that is about 3 percent higher. They used engineering models of bodies moving through fluids—air or water—to determine that the 3 percent difference translates into a 1.5 percent running speed advantage for athletes with the higher belly buttons (i.e., black athletes) and a 1.5 percent swimming speed advantage for athletes with a lower belly button (i.e., white athletes).

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.

We Are All Black (Sort Of)

Race and Genetic Diversity

Y
ou 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.
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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 that 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.