I had the pleasure of reading the stimulating David Epstein's book "The Sports Gene: Inside the Science of Extraordinary Athletic Performance". Some excerpts (and some notes) here below:

Some of the traits that help predict the future pros are behavioral. The future pros not only tend to practice more, but they take responsibility for practicing better

It’s what Durandt hasn’t seen, though, that is telling. “We’ve tested over ten thousand boys,” he says, “and I’ve never seen a boy who was slow become fast.”

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.

Amazingly, the amount of improvement that any one person experienced had nothing to do with how good they were to start.

I do not think it is the same for acquisition of highly-cognitive skills.

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.

"Choose your parents well" never gets old.

That scenario creates what economist Robert H. Frank termed a “winner-take-all” market. As the customer base for viewing extraordinary athletic performances expanded, fame and financial rewards slanted toward the slim upper echelon of the performance pyramid. As those rewards have increased and become concentrated at the top level, the performers who win them have gotten faster, stronger, and more skilled.

Incentives all over again, even if I doubt that in the case track and field became more popular than, say, American Football, we would necessary see new record in the sprinting or throwing events. Current top guys are far in the tail of the distribution in terms of athletic abilities.

In one study, she compared the skeletons of Mistihalj people—a group of medieval Yugoslavian herders—to the skeletons of kids from 1950s Denver. “The herders’ kids are the biggest, buffest kids I’ve ever seen,” she says. “Based on data of modern American children, we’re just puny in terms of the amount of bone we have.” But might a strict childhood training program be able to transform any American tot into a mighty medieval herder? “There’s a lot you can do with activity, and especially starting it earlier,” Cowgill says. “But it’s looking more and more like there’s a genetic component as well.”

Today, the expanding universe of athletic body types is slowing down. Much of the self-sorting, or artificial selection, is finished. The tall athletes are no longer getting taller compared with the rest of humanity at the rate they were two decades ago, nor the small smaller. And the march of constantly shattered world records is slowing right along with it.

Height is an incredibly narrowly constrained trait among humans. Fully 68 percent of American men are in just the six-inch range from 5'7" to 6'1". The bell curve of adult height is a Himalayan slope that falls off precipitously on either side of the mean. A mere 5 percent of American men are 6'3" or taller, while the average height of an NBA player

While inhabitants of the industrialized world grew taller over much of the twentieth century at a rate of about one centimeter per decade—at least partly because of increased protein intake and the decline of growth-stunting childhood infections, and perhaps because people are mixing genes more widely, with “tall” genes dominating “short” genes—NBA players have been growing at more than four times that rate, and the tallest of the tall NBA players at ten times that rate

See here for the increase in mean height of Europeans in the last century

But the “threshold hypothesis” of IQ is not supported by the work of scientists who specialize in that field, nor is the threshold hypothesis of NBA height supported by player data.

Recently over Twitter I wrote that the threshold hypothesis as popularized by Gladwell is tautological (and beyond that probably wrong).

Reaching it required increasing globalization of the game. The average height of American players in the NBA is about 6'6½", while the average height of foreign players is nearly 6'9". A great many of the foreign players in the NBA are there, it seems, because teams ran low on sufficiently tall players at home. Perhaps it’s no surprise, then, that the non-U.S. countries with stable representation in the NBA—Croatia, Serbia, Lithuania—are among the tallest in the world. Because height is a “normally distributed” human trait (i.e., a bell curve), a tiny difference in the average height in a country means a big difference in the number of people at the far extremes, like seven-footers.

This has implications (but it well known to people in the know) for "any" polygenic trait. See this contribution by the late and great James F. Crow.

[About Jamaica] Contemporary letters from British officials show deep respect for the Coromantee, whom one British governor in Jamaica called “born Heroes . . . implacably revengeful when ill-treated,” and “dangerous inmates of a West Indian plantation.” Another Brit, writing in the eighteenth century, said that these “Gold Coast Negroes” were distinguished by “firmness both of body and mind; a ferociousness of disposition . . . an elevation of the soul which prompts them to enterprizes of difficulty and danger.”

Here’s the conclusion of Peter Matthews, the track-and-field statistician who compiled those numbers: “In these days of computer games, sedentary pursuits, and driving our children to school—it is the ‘hungry’ fighter or the poor peasant who has the endurance background, and the incentive to work on it, who makes the top distance runner.”

The Cinderella story is still a must of course.

Interestingly, a system that thrives on the hard work of many is fueled by an abiding belief in natural talent. The Kenyan coaches and runners I spoke with almost uniformly said that it was never too late to begin training. If one has talent, they said, then one just needs to start training hard and elite status will come swiftly.

As psychologist Drew Bailey told me: “Without both genes and environments, there are no outcomes.”

That's a nice one-liner. At the same time, we want to know at the population level how much is explained by nature and how much by nurture. These contributions are only to be estimated at the population level, this is a very important and often overlooked point.

Using the gene frequencies, Folland and Williams made statistical projections of how many “perfect” endurance athletes (people with two “correct” versions of the twenty-three genes) walk the planet.

The paper is here (free access).

Thoroughbreds may have either reached their physiological terminal velocity or simply run out of new athleticism genes within the breeding population. (Thoroughbreds are relatively inbred, with more than half of the genes of modern racehorses tracing back to only four individual horses—the Godolphin Arabian, the Darley Arabian, the Byerley Turk, and the Curwen Bay Barb—that traveled from North Africa and the Middle East to England in the late seventeenth and early eighteenth centuries.)

In the very last line of his paradigm-shattering On the Origin of Species, Charles Darwin says this of his revelation that all the biological variation he sees springs from common ancestry: “. . . from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”

Isn't that cool?