Now I lay me down to sleep

ELECTRIC lighting, television, the internet and caffeine all get blamed for reducing the amount of time people sleep compared with the days before such luxuries existed. Such alleged sleep deprivation is sometimes held responsible for a rise of obesity, mood disorders and other modern ailments. The trouble with this argument, though, is that no one really knows how long people slept before coffee and light bulbs existed.

A study just published in Current Biology by Jerome Siegel of the University of California, Los Angeles and Gandhi Yetish of the University of New Mexico tries to provide an answer. Dr Siegel and Mr Yetish looked at three groups who cleave to pre-industrial (indeed, pre-agricultural) ways of life, to see if their sleep patterns differ from those of wired, urban humanity. To some surprise, they have found that in many ways they do not.