altruism

worker ants tend to take greater risks as they get older. Scientists have shown that this behavioural trait benefits the colony because certain risky activities, such as foraging far from the nest, are best done by ants coming to the end of their useful lives – it doesn't pay to put young workers in high-risk jobs.

As a result, younger ants tend to do housekeeping chores around the nest, which is inherently safer than travelling further afield.

In evolutionary terms, worker ants are the supreme altruists because they dedicate their lives to bringing up the offspring of another individual – their queen – while remaining sterile themselves. This is also true of many other social insects, which perplexed Charles Darwin and generations of biologists who came after him because it appeared to contradict the central idea of evolution – leaving behind as many of your own offspring as possible.