Of course you can choose to get up early (and maybe you can choose to be gay)

‘Oh, I’m an owl,’ said my friend Nick. ‘You’re probably a lark.’ I raised an eyebrow. He explained. Apparently all human beings are either owls or larks, being genetically predisposed to stay up late or get up early, and to be at their best after sundown or dawn.

Nonsense, of course, complete nonsense. Nick just likes partying and his career does not demand his availability much before ten in the morning. The woman friend he had just consigned to the larks section of the human aviary has land and horses, needs to be up before dawn, and not unnaturally begins to flake out after about 9p.m.

None of this has anything to do with genes. Obviously the earlier you rise the earlier you feel like bed, the later you drift off the harder it is to get up early, and we settle into the rhythm and sleep patterns determined by our circumstances, by the pleasures that we seek, or by the willpower we lack.

Willpower (I’ll grant) might be influenced by genes; but it would be strange indeed if Darwinian selection had created two categories of human, the larks and the owls. In rural Africa, I pointed out to Nick, there are no electric lights and everybody goes to sleep around nine. They have to be up well before dawn, because of the heat that comes after sunrise; women have to fetch water, men to work in the cool. Are millions of rural Africans, then, natural owls, living wretched lives as their body clocks fight their circumstances? Or was Nick suggesting all Africans are larks?

But he was having none of my scepticism, and the reason was plain. The cheeky cigar, the midnight brandy, were because dear Nick was an owl, not because he was being self-indulgent.