Authors: David Epstein
At the 1996 Atlanta Summer Olympics, the last that had cheek swabs, 7 women out of the 3,387 competitors—or about 1 in 480—were found to have the SRY gene and androgen insensitivity. The typical rate of androgen insensitivity is estimated to be between 1 in 20,000 and 1 in 64,000. Over five Olympic Games, an average of 1 in every 421 female competitors was determined to have a Y chromosome. So women with androgen insensitivity are vastly overrepresented on the world’s largest sporting stage. Perhaps, then, something about the Y chromosome other than testosterone may be conferring an advantage.
Women with androgen insensitivity tend to have limb proportions more typical of men. Their arms and legs are longer relative to their bodies, and their average height is several inches taller than that of typical women. Like Erika Coimbra, a 5'11" Brazilian volleyball player and 2000 Olympic bronze medalist who is one of the few athletes with androgen insensitivity whose names have ever been made public. (Two of the endocrinologists I spoke with said that XY women are also overrepresented in modeling, because they are often very feminine in appearance in addition to being tall with long legs. Before her personal medical information unfortunately landed in the press, the tall, blond Coimbra had been dubbed the “Brazilian Barbie Doll.”)
The increased height of XY women who are insensitive to testosterone may result from an extended growth period because they don’t heed hormonal
messages or from genes on the Y chromosome that influence height. Men who have an extra Y chromosome tend to be very tall. Dave Rasmussen, the tallest member of Tall Clubs International, is a 7'3" XYY male whose parents are 6'4" and 5'9".
The overrepresentation of XY women only “scratches the surface of intersex conditions in sport,” as a paper in the
British Journal of Sports Medicine
put it. Jeff Brown, a Houston endocrinologist who works with some of the best athletes in America—his patients have fifteen Olympic gold medals, collectively—has treated numerous female Olympians
with a condition called partial 21-hydroxylase deficiency, which can run in families and causes overproduction of testosterone.
In Brown’s estimation, the condition is highly overrepresented among female athletes. “The question would be, does that put them at an advantage over someone who doesn’t have it,” Brown says. “Of course, the answer is yes. But that’s God given. . . . I’ve seen it in jumpers, sprinters, and distance runners.”
No scientist can claim to know the precise impact of testosterone on any individual athlete. But a 2012 study that spent three months following female athletes from a range of sports—including track and field and swimming—showed that the elite-level competitors had testosterone levels that consistently remained more than twice as high as those of the nonelites. And there are powerful anecdotes as well.
Joanna Harper, fifty-five, is a medical physicist who was born male and later transitioned to living as a woman. Harper also happens to be a nationally accomplished age-group runner, and when she started hormone therapy in August 2004 to suppress her body’s testosterone and physically transition to female, like any good scientist, she took data. Harper figured she would slow down gradually, but was surprised to find herself getting slower and weaker by the end of the first month. “I felt the same when I ran,” she says. “I just couldn’t go as fast.” In 2012, Harper won the U.S. national cross-country title for the fifty-five-to-fifty-nine age group, but age and gender-graded performance standards indicate that Harper is precisely as competitive now as a female as she
was as a male. That is, as a female Harper is just as good relative to women as she was relative to men before her transition, but she’s far slower than her own former, higher-testosterone self.
In 2003, as a man, Harper ran Portland’s Helvetia Half-Marathon in 1:23:11. In 2005, as a woman, she ran the same race in 1:34:01. Harper’s male time was about fifty seconds faster per mile than her female time. She has compiled data from five other runners who have transitioned from male to female, and all show the same pattern of precipitous speed decline. One runner competed in the same 5K for fifteen straight years, eight times as a man and then seven times as a woman following testosterone suppression therapy; always faster than nineteen minutes as a man, and always slower than twenty minutes as a woman.
So male-typical hormone patterns (higher testosterone), skeletons (taller height, broader shoulders, denser bones, longer arms, narrower hips), and genes (SRY and others) can confer certain athletic advantages. An interesting evolutionary question, then, is: Why are women athletic at all?
Like our male forebears, our female ancestors needed to be athletic enough to walk long distances, carry kids and firewood, chop down trees, and dig up tubers. But women were far less likely to fight, to run, or to push the capacity of their upper body strength with strenuous activities like tree climbing. Part of the reason that women are as athletic as they are, Geary and several other scientists told me, might be because men are.
Consider a parallel question: Why do men have nipples? The answer is that men have nipples because women do. Nipples are abso
lutely essential for reproductive success in women, and they are not so harmful in men that there has been significant natural selection pressure to get rid of them. As Harvard anthropologist Dan Lieberman, who has studied the role of endurance running in human hunting and evolution, told me, “You can’t program males and females totally separately. You can’t order us like a car in red or blue. Our basic biology is mostly the same, with a little difference. If women didn’t need to run, you could argue that they don’t need the Achilles tendon for springs in their legs. But how would you do that? You would have to have a sex-specific loss of the Achilles.” Instead, nature has left humans with a system whereby—instead of great numbers of genes changing—hormones can selectively activate genes to different effect.
Men and women have almost entirely the same genes. But those small genetic differences—like the SRY gene—induce a cascade of biological consequences that lead to huge disparities on the fields of play. And not just in obvious, fixed characteristics like height and limb length. Men’s muscles grow more rapidly when they lift weights than do women’s. And men’s hearts get bigger faster than women’s in response to endurance exercise. Thus, there are small DNA differences on the Y chromosome that ultimately affect trainability.
And it’s not the only chromosome with genes that do that.
The Talent of Trainability
is grandmother was calling him for dinner, but the boy wouldn’t come. After all, he was pitching a gem, and now he was staring down the other team’s slugger. This could go on for hours, the boy cleaving the air at his grandparents’ house with heaters that ended in dull thuds against the rock wall.
There was no batter, of course, just a boy and his imagination, and his dream to be a pitcher. Or a catcher. Or a third baseman. Or anything, really. It needn’t even be baseball. For as long as the boy could remember, he’d dreamed of being an athlete of any kind and he’d take what he could get. He just wanted to be part of a team, any team. He wasn’t particularly interested in school, so how else could he distinguish himself but with his body?
One day, after watching a
episode on an old black-and-white TV, he raided the cupboards for everything from pickles to Coke and ketchup for the special shake that would give him the power to fly and thereby transform the disappointing shell he was inhabiting. But the super shake was gross, and it didn’t work. Nothing did.
He couldn’t make the church baseball team anymore, not since they started playing with longer baselines. He was too weak to make the throw from third base to first without bouncing it in. And despite being taller than most other kids, he was cut from the junior high
basketball team. So, naturally, the boy found other ways to buoy his foundering self-esteem.
By sixth grade he was cursing and fighting. He talked back to teachers and once got kicked out of school for a day. He hid a plastic tackle box stocked with cigarettes in a bush near his house and would light up every morning before he started his paper route. He idled away hours at the bowling alley, smoking and eating junk food and learning to heist freshly baked pies from a delivery truck that always stopped out back. With that entrée into thievery, soon the boy was applying his five-finger discount to comic books and candy at the corner store. He was beginning to question the God that he had grown up with in the strict Church of Christ.
But even though the boy found his peer approval in rebellion and petty crime, there was a very conformist and very tangible something that he still yearned for: a letterman’s sweater. And there was really only one sport left that he could try in junior high. Track. So he took one last crack at the Curtis Junior High School ninth-grade track team. He had auditioned in previous years, with disastrous results. He couldn’t long jump, and actually managed to knock himself unconscious attempting pole vault. In seventh grade, he crashed through the hurdles, and in eighth grade he pulled a muscle in the 50-yard dash. So this time around, in the spring of 1962, he opted for the longest race the team offered, which happened to be the quarter-mile, or 400-meters; one lap around the track. Before the tryout, he asked God to please let him make this team.
When the PE teacher shouted “Go!” the boy burst to the front. He had found his calling. He was alone in the lead, his feet pounding the track like pistons with just the crackling cinders below and the blue sky in front and above. That lasted for 200 meters. And then his legs turned to bricks and sandpaper enveloped his lungs as several other boys swallowed him up and spit him out the back of their pack. He finished in just under sixty seconds, not good enough to make the team.
Still, he had led the race, however briefly. If he stuck with it, he
might one day be able to run a respectable fifty-two or fifty-three seconds, he figured, and perhaps get that letter sweater. So a few times that summer before he entered high school—which started in tenth grade at Wichita East—he went outside and dashed two blocks from his house and turned around and dashed back before collapsing in the grass. And when the cross-country coach spoke at an assembly that fall, it was as if he was speaking directly at him. “Many of you boys may have done poorly in junior high sports,” the coach said, “but don’t be discouraged. Everyone grows at a different rate and some of you still have plenty of growing to do.” The coach meant it, literally and metaphorically, so the boy went out for the team.
For his first endurance run with the cross-country team the boy was paired with Doug Boyle, another tenth grader who was blessedly like-minded and equally inexperienced. “We turned to each other and said, ‘I’ve never run five miles before without stopping,’” the boy would recall decades later. “‘Let’s help each other. Let’s run slow enough that we can run the whole way.’” And so they did, and they were both elated. And then the going got steeper.
In his first mile time trial, the boy ran 5:38. Not a bad start, but only fourteenth on the team. “Give it up,” his concerned mother urged. “You hardly ate two bites at dinner because you didn’t feel well, and you’re always exhausted.”
“It’s too hard on you,” his father said. But the boy’s teammates were encouraging, and something about running had infected him. The physicality felt good to him. So he stayed out for the team, and a dramatic metamorphosis began.
In his first cross-country race, the boy was only the twenty-first best runner for the school, which landed him squarely on the C-team. But the real training had started, and he could now run ten miles without stopping. Six weeks after the start of the season, on training no different from his C-team peers, the boy moved up to junior varsity. Two months later, and to his own amazement, the boy led the varsity to the Kansas state championship.
Despite his phenomenal improvement, the boy was not set on running. “I loved the feeling of success,” he would one day write, “but how I hated the pain!” So he took the winter off, thinking that perhaps a more pleasant activity might arise to occupy his spring. He daydreamed about competitive weight lifting and thought about how much he really liked golf. But come spring, he found himself out on the track. And again, while some of his peers improved by baby steps, his strides befit a giant.
That March, just six months after his 5:38 mile time trial, and despite a winter free of training, the boy ran a mile race in 4:26 to defeat the defending Kansas state champion. He followed that up with a 4:21 mile. On the team bus trip home, the coach, Bob Timmons, beckoned the boy up front to ask him just how fast he thought he could get. Perhaps 4:18 or 4:19 this year, the boy explained, and maybe 4:10 by the end of his high school career. The coach had other ideas. A decade earlier the coach had seen Roger Bannister prove to the world that a man could indeed run a mile in under four minutes without his legs crumbling to dust. And now, in the boy—in Jim Ryun—the coach saw his own little Bannister. He informed Ryun that he would become the first high school runner to dip under four. He’s crazy, Ryun thought, but the seed was firmly planted.
Ryun would end tenth grade—his first track season—with a 4:08 mile. The following year, he began to train like a professional. He informed his minister that attending church three times a week was not conducive to his goal of breaking four minutes. He regularly pushed through 100-mile training weeks. He lived with his coach in the summer after one season and ran preposterously intense workouts, like forty hard intervals of a quarter-mile each. In his junior year—only his second season of track—he ran the mile in 3:59 and became a national sensation. That summer, he made the 1964 U.S. Olympic team. In 1966, as a nineteen-year-old freshman at the University of Kansas, he ran the mile in a world record time of 3:51.3. The following summer, Ryun burned up a track in Bakersfield, California, in one of the most
outlandish runs in history. These days, world records in distance events almost always come in races that use “rabbits” to set the pace and cut the wind for the athlete making a record attempt. But on June 23, 1967, Ryun broke his own record without the slightest aid from a rabbit or even from his competitors, and on a cinder track, to boot. He led the race from starting gun to finishing tape in a time of 3:51.1, a mark that held for nearly eight years.
He is still remembered as one of the best middle-distance runners of all time. “Be careful those prayers that you pray!” says Ryun, who eventually traded on his athletic feats to become a Republican congressman from Kansas, thinking back on the times he asked the Lord to please at least let him make the track team. In 2007, ESPN ranked Ryun just ahead of Tiger Woods and LeBron James as the greatest American high school athlete of all time.
Without his coach planting the four-minute seed in his mind, and without his zealous training, Ryun likely would have been nothing more than an outstanding high school runner, not an athlete with his own extensive Wikipedia page. But perhaps even more than his world records, it was that 1962–63 period, before Ryun became feverishly dedicated to the goal, which stands out as especially anomalous. In that time he improved from one of the sorriest members of the high school cross country team to the best man on the state’s best team, and then bettered his mile time by ninety seconds from fall to spring to the point that he was running at a pace nearly as fast as he had sprinted a quarter-mile just a year earlier. “I could not explain what was going on,” he would later write of the rapid improvements. “Neither could anyone else.” Not at the time, anyway.
In 1992, a collective of five universities in Canada and the United States began recruiting subjects for a seminal project known as the HERITAGE (HEalth, RIsk factors, exercise Training And GEnetics) Family Study. The universities enlisted ninety-eight two-generation
families to subject their members to five months of identical stationary-bicycle training regimens—three workouts per week of increasing intensity that would be strictly controlled in the lab.
The scientists conducting the study wanted to know how regular exercise would alter these previously untrained folk. How would the strength of their hearts change? Or the amount of oxygen they could use during exercise? How would cholesterol and insulin levels fluctuate? Blood pressure would presumably go down, but how much, and would it be the same for everyone?
Unlike any previous study, DNA would be culled from all 481 participants with the goal of examining whether genes played a part in how fit one person became compared with the next. One of the prime traits of interest for the researchers was what’s known as aerobic capacity, or VO
max, in physiology lingo. Aerobic capacity is a measure of the amount of oxygen a person’s body can use when he or she is running or cycling all out. It is determined by how much blood the heart pumps, how much oxygen the lungs impart to that blood, and how efficient the muscles are at snatching and using the oxygen from the blood as it hurtles past. The more oxygen one can use, the better one’s endurance.
Dr. Claude Bouchard, now of Louisiana State University’s Pennington Biomedical Research Center and mastermind of the HERITAGE Family Study, already had an inkling of what the results would look like. In the 1980s, Bouchard had put a group of thirty very sedentary subjects through identical training plans to see how much their aerobic capacities would increase. Endurance exercise has a profound impact on the human body. More blood is produced and it flows through new capillaries that sprout like roots into muscle. The heart and lungs
strengthen, and energy-generating mitochondria proliferate in the cells.
Bouchard figured he would see some variation in VO
max improvement between people, but “the range from 0 percent to 100 percent change, I did not expect,” he says. It piqued his interest enough that he decided to test identical twins in three different studies, each with a unique training protocol. Sure enough, there were high responders to training and low responders, “but within pairs of brothers, the resemblance was remarkable,” Bouchard says. “The range of response to training was six to nine times larger between pairs of brothers than within pairs, and it was very consistent. That’s how I was able to convince the National Institutes of Health to fund the big study, HERITAGE.” It took four years to gather all the HERITAGE data, and the pattern held there too.
At each of the four centers where volunteers were made to exercise—Indiana University, University of Minnesota, Texas A&M, and Laval University in Quebec—the results of HERITAGE were astonishingly consistent. Despite the fact that every member of the study was on an identical exercise program, all four sites saw a vast and similar spectrum of aerobic capacity improvement, from about 15 percent of participants who showed little or no gain whatsoever after five months of training all the way up to the 15 percent of participants who improved dramatically, increasing the amount of oxygen their bodies could use by 50 percent or more.
Amazingly, the amount of improvement that any one person experienced had nothing to do with how good they were to start. In some cases, the poor got relatively poorer (people who started with a low aerobic capacity and improved little); in others, the oxygen rich got richer (people who started with higher aerobic capacity and improved rapidly); with all manner of variation between—exercisers with a high baseline aerobic capacity and little improvement and others with a meager starting aerobic capacity whose bodies transformed drastically.
Along the improvement curve, families tended to stick together. In
other words, family members generally had similar aerobic benefits from training, while variation between different families was great. Statistical analysis showed that about half of each person’s ability to improve their aerobic capacity with training was determined exclusively by their parents. The amount that any person improved in the study had nothing to do with how aerobically fit he or she was relative to others to begin with, but about half of that baseline, too, was attributable to family inheritance.
In 2011, the HERITAGE research group reported a breakthrough in exercise genetics: they identified twenty-one gene variants—slightly different versions of genes between people—that predict the inherited component of an individual subject’s aerobic improvement. That still leaves the half of aerobic trainability due to other factors, but the twenty-one gene markers had the power to delineate the high and low responders. HERITAGE subjects who had at least nineteen of the “favorable” versions of the genes improved their VO
max nearly three times as much as subjects who had fewer than ten.