Fireside tales

IT SEEMS a universal human rule that the day is for work and the night for play. So a study showing this applies to Kalahari Bushmen as much as to city sophisticates might look unremarkable. But the Ju/’hoansi of northern Botswana do not have electric lighting (or, at least, they did not in the 1970s, when the data in question were gathered). And the gatherer of those data, Polly Wiessner of the University of Utah, wonders whether her recently analysed findings, just published in the Proceedings of the National Academy of Sciences, illuminate a previously unperceived effect on human evolution of the taming of fire.