Why are most of the world's top sprinters from Jamaica?

The 100m finals were held this weekend. Get this:

-- 6 of 8 in the men's final and 4 of 8 in the women's final were from a Caribbean nation.
-- Bolt, a Jamaican, took the gold in the men's final, in world-record time.
-- Fraser, Simpson, and Stewart, all Jamaicans, took gold, silver and bronze, respectively, in the women's final.

That is amazing! Keep in mind, Jamaica, one of the largest Caribbean countries, has a pop. of just 2.8m. By comparison, the U.S. pop exceeds 300m.

And check this out. According to The Guardian,

Bolt's medal took Jamaica's [all time] Olympic total to 43, 42 of which have come on the track and all but one at distances of 400m or under.

What explains this phenomena? One explanation is certainly structural. It doesn't take much to get started as a runner. A pair of shoes? But culture must play a huge role as well. How did this running culture take hold in Jamaica and why has it persisted and [I believe] grown in recent years? And what other explanations are there for the geographic concentration of sprinting talent to such a small portion of the world?

Here is one attempt at an explanation, from the CS Monitor:

How does a poor Caribbean country of less than 3 million people produce such athletic riches? Improved coaching and a new system to develop raw talent at home have combined with a tradition of seeing sprinting as an inexpensive ticket out of poverty, observers say.

This explanation, I suppose, will have to suffice for now.