Letter: Ancestral traits catch us napping

Sir: Tessa Thomas's article extolling the benefits of a siesta ('Take a tip: have a midday kip', 17 August) confirms both personal physical experience and my theory that our tropical ancestry has programmed humans to sleep twice in each 24-hour period - once at night when it is too dark and cold to forage for food, and once at midday when it is too hot to do so. This neatly explains the paradox that while hot afternoons send us to sleep hot nights keep us awake.

Please do not phone me between the hours of 1 and 2pm.

Yours faithfully,

PETER WRAGG

Cambridge

18 August