If that promotes the development of fast-twitch muscle fibres in growing foetuses, that could add to the Jamaican edge. The truth is, we don’t have enough information to draw firm conclusions about the Jamaican dominance of sprinting. But there is good reason to dig deeper – and it has nothing to do with athletics. We now have evidence that extreme stress, heat, cold, malnutrition and pollution (including tobacco smoke) trigger changes in the way genes are activated or silenced.