A few years ago I spent eight months in Ivory Coast and Mali, in the sweltering humidity of Abidjan and the burning, dusty heat of Bamako. It struck me that everyone - whether they were expatriate visitors from colder climates like me or people whose ancestors had lived in West Africa for as far back as anyone can tell - loved air conditioning and would spend money on it even if they were not particularly well off. Of course, some of this could be down to the prestige of this expensive, luxury technology. But I didn't believe that could account entirely for the apparent paradox: given that we evolved in Africa, why do we find it so hard to bear Africa's climate?