Competitive team games in which men test their mettle against others are universal across the world, and may have deep roots in our evolutionary past. Among hunter-gatherers, these games enable men to hone their physical skills and stamina, assess the commitment of their team members, and see how each performs under pressure. All these activities suggest motivation to practise skills involved in lethal raiding, says Michelle Scalise Sugiyama of the University of Oregon in the US, lead author of a study in Springer’s journal Human Nature.