When it comes to human cooperation, it seems that our generosity is governed by how quickly we make decisions. A study in this week’s Nature indicates that our intuitive response is to cooperate; humans tend to be generous when making snap decisions, but act more selfishly when given time to reflect.

Although cooperation is central to human social behaviour, it often requires individuals to incur a personal cost to benefit others, which goes against what self interest should dictate. However, relatively little is known about the cognitive mechanisms that underlie cooperative decision making. David Rand and colleagues use a series of 10 experimental set ups, including both one-shot and repeated games, to investigate whether the gut response is cooperation or selfishness. They find that faster decisions are associated with higher contributions, whereas reflection can undermine these cooperative impulses. The authors propose that our intuitive responses may have been shaped by cultural evolution and the development of social behaviour.