Are humans born to run long distances or short sprints?
One of the most intriguing genes discovered, ACTN3 encodes a protein that governs metabolism in “fast twitch” muscle fibres, which generate force at high speed.Around 18 percent of the world’s population has a truncated variant of the gene which blocks this protein. The stubby variant, called R577X, is common among successful endurance athletes, previous research has found.
On the other hand, elite sprinters, who need explosive speed, are likelier to have the reverse — a functioning variant of ACTN3.
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The apparent reason for this: the loss of ACNT3′s protein was compensated by a different protein, called alpha-actinin-2, which shifted muscle metabolism towards a smoother, more efficient, aerobic pathway.
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North’s team also looked through genetic profiles from individuals of European and East Asian descent and found that there was remarkably little sign of mutation in the wider stretch of genetic code in the vicinity of R577X.Such similarity is a telltale sign of what evolutionary experts call positive selection. Genes which help the fight for survival get lastingly incorporated in the human genome, whereas those that encumber it get weeded out.
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According to North’s calculations, R577X took root among populations in central Europe around 15,000 years ago and in East Asia around 33,000 years ago.