There is nothing like altruism for getting people upset. This discovery of apparently altruistic behaviour in babblers is certain to annoy people. There are some who see altruism as a purely human trait, who believe that the capacity for altruistic behaviour is the difference between human and non-human animals.

Then there are those who must demonstrate that every form of apparent altruism – human or non-human – has an explanation in self-interest. It is possible that our sentinel babblers are, by looking after the group, looking after their own relatives and thus the survival of their genes; or perhaps they are doing it out of reciprocity, doing the job because it will be someone else’s turn on sentry duty next.

There are many examples of nonhuman altruism. Vampire bats are models of altruistic behaviour and will give a hungry neighbour a meal of regurgitated blood; dolphins will keep a sick or injured fellow afloat, safe from drowning, for hours; and wild dogs come back from the hunt and vomit up a meal for those who stayed behind to mind the pups.

I have watched many groups of co-operative breeders in Africa. In this strategy, only one pair from the group breed, but the extended family help to raise the young.

Human beings are not the only altruists. Any co-operative society depends on a degree of flexibility and generosity: a society made up entirely of cheats cannot survive.

There is a continuity between the human and the non-human worlds: and it not something we are comfortable with. The less they are like us, the more comfortable we are with killing them, after all. But, if we pay attention, we find that we have far more in common with animals than we are traditionally led to believe. This leads with dreadful inevitability to the truth that dare not speak its name: that we are animals ourselves.

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