A few days ago, I wrote about a test, now being marketed in the United States, that predicts whether your toddler has more potential as a power athlete or as an endurance athlete. The test examines ACTN3, a gene that affects fast generation of muscular force. Fray poster Andrea Freiboden isn't impressed. "What a lot of crap. Just look at the race of the athlete," she writes:
Generally, people of West African origin have more fast twitch muscles which allow intense bursts of power. This is why running backs, defensive linemen, and receivers are almost all black. We don't need any expensive test. All you have to do is look at the physique. Blacks in basketball are lean and musularly [sic] hard. Whites have softer muscles, which is why white basketball players have to rely more on skill than blacks who have the advantage of skill + great speed/strength.
Oy. I've been through this wringer before. It's true that some racial averages differ in part for biological reasons. It's also true that that this is one of them. But Freiboden is exactly wrong. Race is a less, not more, reliable gauge of physical characteristics than genes are. In fact, that's one of the chief consolations of nontherapeutic genetic testing: No matter how inaccurate genes are as a predictor of this or that ability, they're more accurate than predictions based on race. And the sooner we get past judging by race, the better.
ACTN3 has two key variants: R and X. To recap:
Roughly speaking, the more copies of the R variant you have, as opposed to the X variant, the more likely you are to excel at sports requiring power or speed. (You can be RR, RX, or XX.) The testing company, Atlas Sports Genetics, cites studies that support this pattern. A 2003 analysis of hundreds of athletes who had represented Australia at international meets found that 53 percent of the male competitors in sprinting or power events were RR—nearly twice the prevalence of this genotype in a less-athletic population sample. None of the 35 female sprinters were XX. Nor were any of the 25 male Olympic sprinters. Subsequent studies show the same basic pattern in Finland, Greece, and Russia.
Few genes are known to be decisive in determining life outcomes. Nutrition, training, and other genes matter. But the evidence that this gene significantly influences athletic ability is strong.
Now look at the frequency of the R and X variants in different populations. According to data published seven years ago in Human Molecular Genetics, the relative frequency of the X allele is 0.52 in Asians, 0.42 in whites, 0.27 in African-Americans, and 0.16 in Africans. If you break out the data further, the frequency of the XX genotype is 0.25 in Asians, 0.20 in European whites, 0.13 in African-Americans, and 0.01 in African Bantu. Conversely, the frequency of RR (the genotype for speed and power) is 0.25 in Asians, 0.36 in European whites, 0.60 in African-Americans, and 0.81 in African Bantu. Among Asians, you can expect to find one RR for every XX. Among whites, you can expect nearly two RRs for every XX. Among African-Americans, you can expect more than four RRs for every XX.
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