From the Jamaica Gleaner:
The athletic prowess of Jamaicans
by William Aiken
Dr. William Aiken is the head of Urology at the University Hospital of the West Indies and president of the Jamaica Urological Society
The sprinting prowess of African-Americans and Afro-Caribbean people in general and Jamaicans in particular is legendary and is demanding of serious scientific enquiry and research. It cannot be coincidence that over the years the fastest men and women in the world were born in Jamaica. Herb McKinley, Arthur Wint, Donald Quarrie, Linford Christie, Donovan Bailey, Ben Johnson, Bert Cameron, Michael Frater, Asafa Powell, Merlene Ottey, Sherone Simpson, Veronica Campbell, Deon Hemmings, Bridgette Foster-Hylton and Sanya Richards come readily to mind...
While it is clear that good sport administration, excellent coaching, proper nutrition and adequate funding and facilities are vital to achieving athletic greatness, in the absence of raw athletic sprinting ability this will not occur.
I wish to propose a hypothesis that addresses not only the aspect of Jamaica's raw athletic talent, but also encompasses an explanation of seemingly diverse phenomena as our high incidence of prostate cancer (one study found it to be by far the highest in the world at 304 / 100,000 men / year), our high crime rate (murder capital of the world status earlier this year), our high road traffic accident and fatality rate, and our alleged high levels of promiscuity.
What do these seemingly disparate phenomena, characteristic of Jamaican life, have in common? On close examination these phenomena are manifestations of high levels of aggressiveness and drive, high libidos, highly efficient muscles from persons of lean body mass and black ethnicity.
On closer scrutiny all of these phenomena are either related to high circulating levels of testosterone or alternatively to high levels of responsiveness of testosterone receptors to circulating testosterone. It has already been shown that the testosterone receptors of blacks are different genetically to those of whites and this difference confers increased responsiveness to testosterone.
I've long felt that Occam's Razor points in the same direction. Differences in average levels of male and female sex hormones and in function of sex hormone receptors can parsimoniously account for many of the racial patterns that can't be accounted for by differences in IQ.
I'm not as persuaded, however, that Dr. Aiken's specific theory attributing differences to the Middle Passage is as plausible.
I propose that Jamaicans of primarily African descent have even greater testosterone responsiveness than blacks anywhere else.
But why should this be? I believe the answer to this lies in the slave ship routes within the Caribbean and the New World. First, let us assume that all Africans who survived the trek from the African interior to the West African coast and subsequently the middle passage would have been more or less subject to the same inhumane conditions which would have produced a severe selection pressure that enabled only the fittest slaves to survive the journey.
My hypothesis is that for each incremental increase in the journey travelled, once the slave ships entered the Caribbean, there was a corresponding selection pressure which ensured that only the fittest of the fit slaves survived and furthermore the traits which enabled survival were somehow dependent on high levels of responsiveness to testosterone. Characteristics such as aggression, determination, drive, strong bones, lean body mass, high surface area to body mass ratio, highly efficient and responsive muscles were probably all important for survival and are testosterone-dependent.
The math doesn't really work. Steven Levitt's partner Roland Fryer has revived a similar theory about African-American blood pressure problems being caused by selection for salt retention on slave ships. Greg Cochran explained to Fryer:
"The reason it wouldn't have an important effect is that you don't get a lot of genetic change in one generation unless you try _really_ hard. If they lost the bottom 15% of the people (in terms of salt retention) during the Middle Passage, a cutoff of about one std below average, the increase in salt retention would be about a tenth or so of a standard deviation, assuming a narrow-sense heritability of 50%. You'd never notice the difference."
Nonetheless, Aiken makes an interesting observation about clinal difference within the West Indies:
Since Jamaica was one of the last stops to be made by the slave ships it ensured that only the most resilient and fittest of slaves were alive to disembark in Jamaica. This hypothesis is supported by a number of observations. African-Americans and Afro-Caribbean people are represented far more frequently in sprinting events than persons from Africa. Even more interesting is that as one goes westward within the Caribbean, sprinting prowess becomes more prevalent and reaches its peak by the time Jamaica and Bahamas are reached.
West Indian countries are definitely better at sprinting than West African countries, although the weakness of West Africa at sprinting is often exaggerated. West Africa would be the strongest sprinting region in the world if not for the competition from the West African Diaspora in places like Jamaica and the U.S. I would tend to assume that the West Indian superiority over West Africa is due to advantages in health, nutrition, and social organization, rather than in genetic differences.
What about the clinal difference within the Caribbean? The most striking example is Barbados, whose citizens are renown for being the best educated and most civil of all the West Indians. Barbados was the richest and most easterly of the West Indies.
An alternative theory is that the clinal pattern is due to artificial rather than natural selection. According to the PBS series The Story of English, as the first stop for the slave ships coming from Africa, the wealthy slaveowners of Barbados had their pick, and they preferred to buy slaves from tribes they had found to be the most cooperative. Then they'd send the leftovers from the Bad Dude tribes on to be sold in Jamaica and the U.S.