The Sports Gene: Inside the Science of Extraordinary Athletic Performance

Chapter 8 launches a discussion of height in sports, especially in basketball, with an anecdote about NBA Hall-of-Famer Dennis Rodman, who didn’t excel at basketball until after he’d grown to his height of 6’8” around the age of 21. Epstein explains that “height is an incredibly narrowly constrained trait among humans” (130), meaning that most humans fall within a rather narrow range of heights. Among professional basketball players, however, the average height goes up, and players earn more based on their height. In the 1980s, when NBA players began participating in league profits, the monetary value of a career in basketball shot up, and “NBA teams began scouring the globe for giants” (132). Even the shorter players in the NBA have long arm spans to compensate for their lack of height.

Epstein broadens the discussion about height to its genetic influences and expressions in populations across the globe. He claims that “the permutations of size-determining interactions between nature and nurture are fathomless” (137), meaning that height is a trait influenced both by genes and by environment. Epstein provides the example of European children during World War I and World War II who experienced stunted periods of growth due to famine, but whose growth sped up after the wars, delivering them to normal full adult heights.

Experts also find that people with "recent African ancestry” across all sports tend to have narrower hips and longer limbs (138). This distinction plays out in the gap between white and black NBA players. Limb length, and therefore height, are also affected by a population’s proximity to the equator. Because greater surface area allows for a greater ability to radiate heat and cool the body, there was a natural selection for individuals with longer limbs within populations in warm locations.

In 2010, a study found that black adults had, on average, a center of mass higher than white adults, making black adults more effective at running and white athletes more effective at swimming. The researchers, according to Epstein, “did a backbend to avoid racial stereotyping. ‘Our study does not advance the notion of race,’ they wrote” (141). Epstein admits that social factors may limit an athlete’s access to training in sports, but he closes with the claim that running, a sport with “few barriers to entry” (141), is dominated by black athletes and that it would be wrong to ignore this fact. 

Chapter 9 tracks the findings of Yale geneticist Kenneth Kidd, which include the discovery that “there was more genetic variation among Africans from a single native population than among people from different continents outside of Africa” (143). This finding supports the “‘recent African origin’ model” (143), which holds that “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” (144). The groups that migrated off the African continent were small compared to their source population, resulting in less genetic variation within populations that descended from those groups.

Because the greatest genetic variety exists on the African continent, it’s probably true 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” (145). Kidd supposes that individuals with African descent, and not Africans on average, therefore “do have a genetic advantage in sports” (145).

Epstein then discusses genetic variations as they evolved according to certain populations: “as ancestral humans spread cross 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” (147). Lactose intolerance is one genetic trait whose distribution amongst populations is explainable by this theory.

Genetically speaking, because of our relative youth vis-à-vis the planet’s history, humans are highly similar. However, Epstein argues, our differences make an impact. According to a Stanford press release, “people’s self-identified race/ethnicity is a nearly perfect indicator of their genetic background” (149). Epstein adds that “skin color is already being used as a proxy, albeit often a crude one, for underlying genetic information” in medical research (150). A genotype is the combination of genes, while a phenotype is the physical expression of those genes. One question that remains unanswered is whether having the greatest diversity of genotypes, which Africans do, means having the “greatest diversity of athletic phenotypes” (151).

Epstein closes with a detailed, step-by-step account of research conducted by geneticist Kathryn North on the ACTN3 gene, which codes for the alpha-actinin-3 structural protein that’s found in fast-twitch muscle fibers. She found that one variant of that gene, called the X variant, stopped production of that protein. Her research found that the X variant “had been favored by natural selection only in non-African environments” (154), that almost no elite sprinters had two X variants, and that “nearly all of the control subjects from African populations” had the protein in their fast-twitch muscles (155). North concluded, therefore, that ACTN3 must be a “gene for speed” (155). Private gene-testing companies have developed tests for the ACTN3 gene, though Epstein argues “the inherited component of complex traits, like athleticism, is most often the result of dozens or even hundreds or thousands of interacting genes, not to mention environmental factors” (157).