What makes Jamaicans such champion sprinters? Is it a combination of nature and nurture?

Runners of West African descent—which includes Jamaicans as well as most African-Americans—seem to be built for speed. 

Several biological factors may be coming into play here. One study conducted in Quebec in the 1980s found that black West African students had significantly higher amounts of "fast-twitch" muscle fibers—the kind that are responsible for short, explosive bursts of action—than white French Canadians did. (So far, there is no evidence that even extensive training can turn slow-twitch muscles into fast-twitch ones, though moving in the other direction is possible.)  

Exercise physiologists at the University of Glasgow and the University of the West Indies are currently researching the genetic, nutritional, and sociological factors behind West Africa's sprinting success.  The team has just begun to analyze the genetic data it has collected, but preliminary findings suggest that 70 percent of Jamaicans have the "strong" form of the ACTN3 gene—which produces a protein in their fast-twitch muscle fibers that has been linked to increased sprinting performance. 

That's a significantly higher percentage than in the United States, where about 60 percent have the gene variant. A further 28 percent of Jamaicans are heterozygous for the gene—which has the same effect, but to a lesser degree—compared with about 20 percent of Americans. 

The rest, by contrast, have the "null" form of the gene that produces no protein at all, apparently making for lousier sprinters but perhaps better endurance runners. (Ironically, a sample of Kenyans showed a lower incidence of the null form than Americans.)