At Chimfunshi Wildlife Orphanage in Zambia, a male chimpanzee wraps his arms around another from behind. A second male joins the embrace. Then a third, then a fourth, until the whole cluster has folded into what the researchers who watched it happen started calling a reassurance train. It happened in the minutes before feeding, the exact window when a restricted food source is about to turn a peaceable group into a jostling one.
That observation, made by Jake Brooker and colleagues at Durham University, became the seed of a study just published in Proceedings of the Royal Society B.1 The question underneath it is simple enough to state and surprisingly hard to test: does touching each other before a fight over food actually stop the fight from happening?
