Two years ago, a group of Ugandan chimps provided a blow to the idea that humans are the only animals that truly behave selflessly to one another. These chimps showed clear signs of true selflessness, helping both human handlers and other unrelated chimps with no desire for reward.

The question of why we help each other, instead of looking out for ourselves, is one of the most compelling in modern biology. Evolutionary and game theory alike predict that selfish behaviour should be the rule with altruism the exception, and animal experiments have largely supported this idea. Nature, ‘red in tooth and claw’, is painted as a fierce competition between selfish individuals and their even more selfish genes. In this stark