There is a robin raising her young just outside my window. I know because every time we let the cats out, she becomes very agitated, hopping from perch to perch, chattering loudly, presumably as she tries to distract the cats away from the nest.

Evolutionary psychology would suggest that this is altruism in action. The robin is prepared to put her own life at risk for the sake of her young. From the point of view of her genes, as it were, it is better that she die and the chicks live, for then the genes will be expressed in another generation.

This is a plausible explanation to a degree, though if you look at it more closely, it seems flaky. For one thing, if the robin dies then presumably her chicks will too, they being abandoned in the nest. So the wise robin will not risk her life but ensure that she distracts the predator without doing so. In other words, she could be acting selfishly as much as altruistically, her own life being worth saving quite as much as that of her young.

Alternatively, even if this could be called altruism, it is a limited sort of altruism. The robin will only seek to distract the cats from her young: she shows kin group preference. Human altruism can certainly manifest itself when there is a close genetic connection. But it is not limited by those bonds, the fireman risking his life for complete strangers, and so on.

Then there is something else. I wrote about what the 'wise' robin will do. But, of course, a robin is not wise: she acts instinctually. (Presumably her genes, and other related factors, are responsible for that.) Human beings, though, are different because they think, at least sometimes. And when thinking is linked to action, it can often take us in a completely different direction from the instinctive.

Surely the non-instinctive is a necessary part of any account of altruism too: the soldier signs up against certain instincts of self-preservation, and undergoes a rigourous training so that when the moment comes, and they find themselves at the wrong end of a gun, their innate instincts have been completely replaced by the honour code of the military, and they are prepared to die. In so doing, they become a hero, with the suggestion that willed commitment - not the instinctive commitment of the robin - is at least part of altruism proper.

Actually, it you read evolutionary psychology, it is far from clear that there is a consistent account of altruism available. In one book it will say that morality is an adaptation, with the same ontological status as, say, teeth, and therefore altruism is an illusion of the genes. But then in another book you can read of the need for evolutionary psychology to have an absolute commitment to the genuine nature of human altruism. Even Richard Dawkins famously concludes his book The Selfish Gene with the comment that humans alone can rebel from the tyranny of the 'selfish replicators'. (And to be fair to the sociobiologists, it is not as if philosophers have arrived at an unequivocal account of altruism either.)

Having said all that, there is still something quite moving about the behaviour of the robin outside my window. She seems brave. Maybe that feeling is a pure anthropomorphism on my part. But it is enough to distract me. I must get the cats in.