Isegoria

In a 72-week trial in participants with obesity, tirzepatide — a novel glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 receptor agonist — provided substantial and sustained reductions in body weight. Participants lost one-fifth of their body weight.

Among 14,000 Finnish people who were tracked for 40 years, those who used saunas frequently were way less likely to develop dementia:

Big if true. And that’s an impressively huge study! But let’s start peeling back the layers.

First of all, it wasn’t every sauna enthusiast who reaped the supposed protective effect against dementia; it was specifically those who used a sauna 9-12 times a month. Sauna bathers who hit the wooden bench 5-8 times a month — sorry, no effect. And those who went more than 12 times a month — again, no luck.

That should raise a caution flag in your head. When only a very specific subpopulation in a study experiences a benefit, it may indeed be that there is some extremely nuanced sweet spot. But it is more likely that the researchers collected a lot of data, which in turn allowed them to analyze many different correlations between sauna use and dementia; the more different analyses they can do, the more likely some of those analyses will generate false positives, just by statistical chance. And then, of course, those titillating positive results are the ones that end up at the top of the paper, and in the press release.

The protection against dementia for that 9-12-times-per-month set was big over the first 20 years of the study, and then faded later, so now we’re slicing and dicing data not only by sauna-frequency, but by time. And then there’s temperature. The Finns who saunaed in temperatures hotter than 100°C (212°F) actually had a higher risk of dementia than those who sauna-and-chilled below 80°C (176°F).

So if you want to prevent dementia, hit the sauna precisely 9-12 times a month at below 80°C — and, unfortunately, expect the protective effect to diminish in the future. Whew!

Alex Hutchinson reviews a recent study on the physiology of treading water efficiently:

They put 21 volunteers, all experienced water polo players, synchronized swimmers, or competitive swimmers who self-identified as water treading experts, through a series of physiological and cognitive tests while performing four different styles of treading. The verdict: some techniques really are substantially better than others.

The four techniques are as follows:

1. Running in the water: This one is pretty self-explanatory. Hands and feet are moving up and down in a running-like motion.
2. Flutter kick: Your hands are sculling back and forth along the surface of the water, while your legs do a flutter kick.
3. Upright breaststroke: Your hands are still sculling along the surface of the water, but your legs are doing the distinctive frog kick of the breaststroke.
4. Eggbeater: It’s similar to the upright breaststroke, with the key difference that your legs are kicking one at a time instead of synchronously, producing an eggbeater pattern of alternating circles with each leg.

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There were clear differences in how efficient the different techniques were, with running and flutter kick performing equally poorly, and upright breaststroke and eggbeater performing equally well. This pattern showed up in every outcome measure.

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Normally VO2 measurements are adjusted for weight, since heavier people burn more energy — but in this case, wet weight was used to also account for differences in buoyancy.

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The two inferior techniques largely rely on pushing down against the water to move the body upward. This has two problems: water is too thin to provide much support, and even when the pushing works you get a lot of wasted up-and-down motion. The two better strokes, in contrast, involve lateral movements of the arms and legs: your cupped hand acts like an airplane wing or sailboat sail, generating lift forces perpendicular to the plane of motion. This is more efficient than pushing on the water, and produces less wasted vertical bobbing.

There’s one key difference between upright breaststroke and the eggbeater: in the former, your legs are kicking outward at the same time, while in the latter they’re alternating. This means that breaststroke produces some of that undesired up (when you kick) and down (between kicks) motion — and that effect is exacerbated if you stop sculling with your hands. In the eggbeater, there’s always one leg moving, so you get a smoother, more continuous lift that can keep you up even without your hands. The study didn’t test anything that required using your arms — but if you want to throw a water polo ball, strike a fancy pose during your synchro routine, or signal frantically to a passing ship that you need rescue, eggbeater looks like a much better bet.

Collagen is sometimes referred to as the body’s glue, David Epstein explains (in The Sports Gene), holding connective tissues in proper form:

Biologists at South Africa’s University of Cape Town have been leading the way in identifying genes that predispose exercisers to injuring tendons and ligaments. The researchers focused on genes like COL1A1 and COL5A1 that code for the proteins that make up collagen fibrils, the basic building blocks of tendons, ligaments, and skin.

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People with a certain mutation in the COL1A1 gene have brittle bone disease and suffer fractures easily. A particular mutation in the COL5A1 gene causes Ehlers-Danlos syndrome, which confers hyperflexibility. “Those people in the old days of the circus who used to fold themselves into a box, I bet you in most cases they had Ehlers-Danlos syndrome,” says Malcolm Collins, one of the Cape Town biologists and a leader in the study of collagen genes. “They could twist their bodies into positions that you and I can’t because they’ve got very abnormal collagen fibrils.”

Ehlers-Danlos syndrome is rare, but Collins and colleagues have demonstrated that much more common variations in collagen genes influence both flexibility and an individual’s risk of injuries to the connective tissues, like Achilles tendon rupture. Using that research, the company Gknowmix offers collagen gene tests that doctors can order for patients.

The apolipoprotein E gene comes in a number of common variants, and a single copy of the Apo4 variant is associated with a threefold increased risk of Alzheimer’s, David Epstein explains (in The Sports Gene), but it also extends beyond Alzheimer’s to how well the brain recovers from any injury:

A 1997 study determined that boxers with an ApoE4 copy scored worse on tests of brain impairment than boxers with similar length careers who did not have an ApoE4 copy. Three boxers in the study had severe brain function impairment, and all three had an ApoE4 gene variant. In 2000, a study of fifty-three active pro football players concluded that three factors caused certain players to score lower than their peers on tests of brain function: 1) age, 2) having been hit in the head often, and 3) having an ApoE4 variant.

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What went entirely unmentioned in media coverage, though, was that five of nine brain-damaged boxers and football players who had genetic data included in the report had an ApoE4 variant. That’s 56 percent, between double and triple the proportion in the general population.

In The Sports Gene David Epstein reports on a “controversial” hypothesis about ADHD — or “hyperactivity”:

A set of scientists have proposed the controversial idea that hyperactivity and impulsivity may have had advantages in the ancestral state of man in nature, leading to the preservation of genes that increase ADHD risk. Interestingly, the 7R variant of the DRD4 gene is more common in populations that have migrated long distances, as well as those that are nomadic, compared with settled populations.

In 2008, a team of anthropologists genetically tested Ariaal tribesmen in northern Kenya, some of whom are nomadic and some recently settled. In the nomadic group — and only in the nomadic group — those with the 7R version of the DRD4 gene were less likely to be undernourished.

All sixteen human studies conducted as of the writing of The Sports Gene had found a large contribution of heredity to the amount of voluntary physical activity that people undertake, David Epstein reports:

A 2006 Swedish study of 13,000 pairs of fraternal and identical twins — fraternal twins share half their genes on average, while identical twins essentially share them all — reported that the physical activity levels of identical twins were twice as likely to be similar as those of fraternal twins.

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But another, smaller study of twin pairs that used accelerometers to measure physical activity directly found the same difference between fraternal and identical twin pairs.

The largest study, of 37,051 twin pairs from six European countries and Australia, concluded that about half to three quarters of the variation in the amount of exercise people undertook was attributable to their genetic inheritance, while unique environmental factors, like access to a health club, had a comparatively puny influence.

It is entirely clear that the dopamine system responds to physical activity. This is one reason that exercise can be used as part of treatment for depression and as a method to slow the progression of Parkinson’s disease, an illness that involves the destruction of brain cells that make dopamine. And there is evidence that the reverse is true as well, that physical activity levels respond to the dopamine system.

Scientists who bred rodents for their desire to run have proven that work ethic is genetically influenced, David Epstein explains (in The Sports Gene):

Normal mice run three to four miles each night.

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Garland took a group of average mice and separated them into two subgroups: those that chose to run less than average each night, and those that chose to run more than average. Garland then bred “high runners” with other high runners, and “low runners” with other low runners. After just one generation of breeding, the progeny of the high runners were, of their own accord, running even farther on average than their parents. By the sixteenth generation of breeding, the high runners were voluntarily cranking out seven miles each night.

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When mice are bred for endurance capacity — not voluntary running, but when they are forced to run as long as they physically can — successive generations have more symmetrical bones, lower body fat, and larger hearts.

In his voluntary-runner breeding program, Garland saw body changes, “but at the same time,” he says, “clearly the brains are very different.” Like their hearts, the brains of the high runners were larger than those of average mice. “Presumably,” Garland says, “the centers of the brain that deal with motivation and reward have gotten larger.”

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Whatever Ritalin does in the brains of normal mice is already occurring in the brains of the high-running mice.

Kenya’s long-distance runners live at altitude, David Epstein notes (in The Sports Gene), but some people ask, “If it’s just the altitude, where are the runners from Nepal?”:

The “Nepali runners” question, though, is actually irrelevant to the Kenyan and Ethiopian running phenomena, and not only because the Himalayan climate does not foster a narrow body type. One clear point of science is that the genetic means by which people in different altitudinous regions of the world have adapted to life at low oxygen are completely distinct. In each of the planet’s three major civilizations that have resided at high altitude for thousands of years, the same problem of survival is met with different biological solutions.

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By the late nineteenth century, scientists figured they understood altitude adaptation. They had studied native Bolivians, living in the Andes at higher than thirteen thousand feet. At that altitude, there are only around 60 percent as many oxygen molecules in each breath of air as at sea level. In order to compensate for the scarce oxygen, Andeans have profuse portions of red blood cells and, within them, oxygen-carrying hemoglobin.

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Andeans have so much hemoglobin that their blood can become viscous and unable to circulate well, and some Andeans develop chronic mountain sickness.

Nineteenth-century scientists also saw that Europeans who traveled from sea level to altitude responded the same way, by producing more hemoglobin.

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Cynthia Beall, an anthropology professor at Case Western Reserve University in Cleveland, started visiting to study Tibetans and Nepalese Sherpas who can live as high as eighteen thousand feet. To her surprise, Beall found that Tibetans had normal, sea-level hemoglobin values, and low oxygen saturation, lower than people at sea level.

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Most Tibetans have a special version of a gene, EPAS1, that acts as a gauge, sensing the available oxygen and regulating the production of red blood cells so that the blood does not become dangerously thick. But it also means Tibetans don’t have the increase in oxygen-carrying hemoglobin that Andeans do.

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Eventually, Beall determined that Tibetans survive by having extremely high levels of nitric oxide in their blood. Nitric oxide cues blood vessels in the lungs to relax and widen for blood flow. “The Tibetans have 240 times as much nitric oxide in the blood as we do,” Beall says. “That’s more than in people at sea level who have sepsis,” a life-threatening medical condition. So Tibetans adapted by having very high blood flow in their lungs, and they also breathe deeper and faster than native lowlanders, as if they’re in a constant state of hyperventilation.

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In 1995, Beall and a team moved on to the remaining population in the world that has lived at high altitude for thousands of years: Ethiopians, and specifically the Amhara ethnic group living at 11,600 feet along the Rift Valley. Yet again, she found an altitude biology unique in the world. The Amhara people had normal, sea-level allotments of hemoglobin and normal, sea-level oxygen saturation.

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But Beall has preliminary data on Amhara Ethiopians that shows they move oxygen unusually rapidly from the tiny air sacs in their lungs into their blood.

David Epstein explores (in The Sports Gene) Kenya’s dominance in long-distance running:

In the 1964 Olympics, just the third ever in which Kenya competed, a Kipsigis runner named Wilson Kiprugut won bronze in the 800-meters. Four years later, in the altitude of Mexico City, Kenya was the dominant distance running power, winning seven medals in middle- and long-distance events.

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“The conventional wisdom was that blacks could sprint, but that anything that required tactical sophistication, or discipline, or training,” he says, “this was the white man’s province.”

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The 4.9 million Kalenjin people represent about 12 percent of Kenya’s population, but more than three quarters of the country’s top runners.

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Manners wrote that a part of traditional life for Kalenjin warriors was the practice of cattle raiding. Essentially, it entailed stealthily running and walking into the land of neighboring tribes, rounding up cattle, and escorting them back to Kalenjin land as quickly as possible. Cattle raiding was not considered theft so long as the raiders weren’t filching the cattle from the same subtribe within the Kalenjin. “The raids were conducted largely at night,” Manners wrote, “and sometimes ranged over distances as great as 100 miles! Most raiding parties were group ventures but each muren [or warrior] was expected to at least do his share.”

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A muren who brought back a large number of cattle from a raid was hailed as a courageous and athletic warrior and could use his cattle and prestige to acquire wives.

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Korir was thrust into the 3,000-meter steeplechase — a race just shy of two miles that includes hurdles — and in his third-ever attempt at the event won the national junior college championship. Four years later, Korir was the third-ranked steeplechase runner in the world.

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Or the one about Julius Randich, who arrived at Lubbock Christian University in Texas a heavy smoker with no competitive running background. By the end of his first year, 1991–92, Randich was the national small-colleges (NAIA) champion in the 10K. The following year, Randich set NAIA records in the 5K and 10K and was named the outstanding athlete in any sport in the NAIA.

Kalenjin runners became all the rage among NAIA coaches, and several others would win the 10K national championships after Randich, including his younger brother Aron Rono, who won it four straight times.

Rotich, the son of a prosperous Kalenjin farmer, arrived at South Plains Junior College in Texas in 1988, having lived a “comfortably sedentary” life, as Manners describes it. Rotich, a stout 5’8″ and 190 pounds, quickly burned through most of the $10,000 his father had given him for two years of living expenses and tuition. “But rather than return home in disgrace,” Manners wrote, “Paul . . . decided to train in hopes of earning a track scholarship.” Rotich trained at night to avoid the embarrassment of being seen. That concern would be short-lived, as he made the national junior college cross-country championships in his first season. He went on to become a ten-time All-American in cross-country and indoor and outdoor track. As Manners reported, when Rotich returned to Kenya and detailed his running exploits to a cousin, the cousin replied: “So, it is true. If you can run, any Kalenjin can run.”

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Consider this: seventeen American men in history have run a marathon faster than 2:10 (or a 4:58 per mile pace); thirty-two Kalenjin men did it just in October 2011.

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For example: five American high-schoolers have run under four minutes in the mile in history; St. Patrick’s High School, in the Kalenjin training town of Iten, once had four sub–four milers in school at the same time.

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Wilson Kipketer, a former St. Patrick’s student who became a Danish citizen and held the 800-meter world record from 1997 to 2010, does not hold his own high school’s record.

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The kids in his time trials generally come from elite, highly selective, government-funded boarding schools, and essentially none of them have any racing experience.

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Each year, about half of the boys in the time trial will run faster than 5 minutes and 20 seconds in the 1,500-meter time trial, on a shoddy dirt track, above seven thousand feet. (The 1,500 is about 100 meters shy of a mile, and 5:20 translates to a mile time just over 5:40.)

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In the tryout in 2005, a boy named Peter Kosgei ran 4:15 with no real training. Kosgei was accepted to Hamilton College in Clinton, New York, and quickly became the best athlete in the college’s history. In his freshman year, Kosgei won the Division III 3,000-meter steeplechase national title. By the end of his junior year, he had compiled eight more national titles in cross-country and track.

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Evans Kosgei — no relation to Peter — held down a 3.8 GPA in computer science and engineering at Lehigh University and, after adjusting to life in America for a year, decided to go out for cross-country in his sophomore year. He struggled even to finish his five-mile tryout. But, in short order, Kosgei was running at the Division I national championships in both cross-country and track. In 2012, he was named Lehigh’s Graduating Scholar-Athlete of the Year.

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As expected from their latitudes of ancestry, though, the Kalenjin and Danish boys did display body type differences. A greater portion of the body length of the Kalenjin boys was composed of legs. The Kalenjin boys were, on average, two inches shorter than the Danish boys, but had legs that were about three quarters of an inch longer.

The scientists’ most unique finding, though, was not the length of the legs, but their girth. The volume and average thickness of the lower legs of the Kalenjin boys was 15 to 17 percent less than in the Danish boys. The finding is substantial because the leg is akin to a pendulum, and the greater the weight at the end of the pendulum, the more energy is required to swing it.

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Compared with the Danish runners, the Kalenjin runners tested by the Danish scientists had nearly a pound less weight in their lower legs. The scientists calculated the energy savings at 8 percent per kilometer.

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Some anthropologists actually refer to the extreme of a slender body build as the Nilotic type — “Nilotic” refers to a set of related ethnic groups residing in the Nile Valley — and, it so happens, the Kalenjin are a Nilotic people.

The Nilotic body type evolved in low latitude environments that are both hot and dry, because the long, thin proportions are better for cooling.

(Conversely, the extreme of the short, stocky build was historically known as the Eskimo type, though the term “Eskimo” has been replaced in some countries, where it is considered derogatory.)

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Anthropologist Vincent Sarich used world cross-country championship results to calculate that Kenyan runners outperformed all other nations by 1,700-fold. Sarich made a statistical projection that about 80 out of every 1 million Kenyan men have world-class running talent, compared with about 1 out of every 20 million men in the rest of the world.

A 1992 Runner’s World article noted, based purely on population percentages, the statistical chances of Kenyan men having won the medals they did at the 1988 Olympics was 1 in 1,600,000,000.

Allen’s rule of body proportions dictates that people from low latitudes and warm climates have long limbs, and Bergmann’s rule dictates that they have narrower builds with slimmer pelvic bones, David Epstein explains (in The Sports Gene), but there’s another, less anatomical reason for western African sprinting dominance:

In 2006, Morrison, with Patrick Cooper, proposed in the West Indian Medical Journal that rampant malaria along the west coast of Africa, from where slaves were taken, led to specific genetic and metabolic alterations beneficial for sprint and power sports. The hypothesis: that malaria in western Africa forced the proliferation of genes that protect against it, and that those genes, which reduce an individual’s ability to make energy aerobically, led to a shift to more fast-twitch muscle fibers, which are less dependent upon oxygen for energy production. Morrison helped with the biology details, but the fundamental idea originally came from Cooper, a writer and childhood friend of Morrison’s.

Cooper was a polymath who had professional success in jobs ranging from music recording to writing speeches for Norman Manley, an architect of Jamaica’s independence, and then for his son, Prime Minister Michael Manley. Early in his career, Cooper had been a reporter for The Gleaner, Jamaica’s largest newspaper. Working at The Gleaner’s sports desk, he first surmised that white athletes had historically dominated sprint and power sports only by systematically excluding or dodging black athletes, like boxing champion Jack Johnson. In later writing, Cooper meticulously documented the fact that athletes with western African heritage become highly overrepresented in sprint and power sports almost immediately once they are allowed a fraction of their white counterparts’ access to sports.

At every Olympics after the U.S. boycott of 1980, every single finalist in the men’s Olympic 100-meters, despite homelands that span from Canada to the Netherlands, Portugal, and Nigeria, has his recent ancestry in sub-Saharan West Africa.

(The same has been true for women at the last two Olympics, and all but one female winner since the U.S.-boycotted 1980 Games has been of recent western African descent.)

And there has not been a white NFL player at cornerback, football’s speediest position, in more than a decade.

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Cooper found the famous body types study of 1968 Olympians, and he latched on to a curious side note recorded by the scientists. The researchers had been surprised to find that “a sizeable number of Negroid Olympic athletes manifested the sickle-cell trait.”

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In 1975, the year after the Mexico City Olympics data was published, another study appeared that Cooper would dissect two decades later, this one showing naturally low hemoglobin levels in African Americans.

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Using data from nearly 30,000 people in ten different states, with ages ranging from the first year to the ninth decade, it reported that African Americans have lower hemoglobin levels at every stage of life than white Americans, even when socioeconomic status and diet are matched.

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Like sickle-cell trait, genetically low hemoglobin — all else being equal — is a genetic disadvantage for endurance sports. Runners of recent western African descent are very much underrepresented at high levels of distance running. (The Jamaican record in the 10K would not even have qualified for the 2012 Olympics)

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And then Cooper found just the potential “compensatory mechanism” he was looking for, in a 1986 study from Laval University in Quebec published in the Journal of Applied Physiology and coauthored by Claude Bouchard, who would go on to become the most influential figure in the field of exercise genetics, and the leader of the HERITAGE Family Study that documented aerobic trainability differences among families.

Bouchard and colleagues took muscle samples from the thighs of two dozen sedentary Laval students, primarily from countries in western Africa, as well as from two dozen sedentary white students, who were identical to the African students in age, height, and weight. The researchers reported that a higher proportion of muscle in the African students was composed of fast-twitch muscle fibers, and a lower proportion was slow-twitch muscle fibers compared with the white students. The African students also had significantly higher activity in the metabolic pathways that rely less on oxygen to create energy and that are engaged during an all-out sprint.

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In his 2003 book, Black Superman: A Cultural and Biological History of the People Who Became the World’s Greatest Athletes, and then in his 2006 paper with Morrison, Cooper first made the argument that West Africans evolved characteristics like a high prevalence of the sickle-cell gene mutation and other gene mutations that cause low hemoglobin for protection from malaria, and that an increase in fast-twitch muscle fibers followed from that, providing more energy production from a pathway that does not rely primarily on oxygen, for people who have reduced capacity to produce energy with oxygen.

The former part of Cooper’s hypothesis — that sickle-cell trait and low hemoglobin are evolutionary adaptations to malaria — now seems undeniable.

In 1954, the same year Sir Roger Bannister broke the four-minute mile, British physician and biochemist Anthony C. Allison, who had been raised on a farm in Kenya, showed that sub-Saharan Africans with sickle-cell trait have far fewer malaria parasites in their blood than inhabitants of the same region who do not have sickle-cell trait.

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Cooper and Morrison’s suggestion that low hemoglobin in African Americans and Afro-Caribbeans is a second adaptation to malaria has been proven true as well, in a deadly manner.

Even as evidence mounted that low hemoglobin levels in Africans native to malarial zones is at least partly genetic, aid workers in Africa looked upon low hemoglobin as a sign purely of a diet with too little iron. In 2001, the United Nations General Assembly charged the world with reducing iron deficiency among children in developing nations. And so, in a well-intended effort to improve nutrition, health-care providers descended on Africa with iron supplements, which raise the hemoglobin levels of those who consume them.

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The problem was that doctors who studied malarial regions saw increased cases of severe malaria wherever iron supplements were dispensed. Since the 1980s, scientists working in Africa and Asia had documented lower rates of malaria death in people with low hemoglobin levels. In 2006, following a large, randomized, placebo-controlled study in Zanzibar that reported a stark increase in malaria illness and death among children given iron supplements, the World Health Organization issued a statement backtracking from the earlier UN position and cautioning health workers about giving iron supplements in areas with high malaria risk. Low hemoglobin, like sickle-cell trait, is apparently protective against malaria.

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About 12 percent of Ivorian citizens are sickle-cell carriers, and in the early 1980s Le Gallais noticed that the top three female Ivorian high jumpers (one of whom won the African championship) became abnormally exhausted during workouts. Le Gallais tested the athletes and found — “surprisingly,” he wrote in an e-mail — “these three athletes were sickle cell trait carriers, despite originating from different ethnic groups in the country.”

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In 1998, he reported that nearly 30 percent of 122 Ivorian national champions in explosive jumping and throwing events were sickle-cell trait carriers, and that they collectively accounted for thirty-seven national records. The top male and female in the group were both sickle-cell carriers.

Repeatedly, studies of families and twins find the heritability of height to be about 80 percent, David Epstein explains (in The Sports Gene):

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.

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Similarly, female gymnasts delay their growth spurt with furious training, but that does not diminish their ultimate adult height.

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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.

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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.

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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.

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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.

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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.

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“So maybe it’s not so much that white men can’t jump. White men just can’t reach high.”

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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.

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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.

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Africans with ancestry in southern regions of the continent, farther from the equator, do not necessarily have especially long limbs.

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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).