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People still debate whether humans are genuinely altruistic by nature

If you believe there is no such thing as altruism, you are in good company. In The Selfish Gene, Richard Dawkins writes that we must “try to teach generosity and altruism, because we are born selfish”. Even if we are nice to members of our family, that doesn’t count because there is a pay-off, at least in biological terms: they share some of our genes, so by helping them we indirectly further our own genetic immortality. Meanwhile, other acts of seeming altruism are often just reciprocity. If you scratch my back, then I scratch yours – no matter how much later – that’s not selfless either.

This all makes good evolutionary sense, since spending time and energy helping someone without any return puts you at a distinct disadvantage in the survival stakes. The only trouble is that in recent years evidence has amassed that people do commit acts of genuine altruism. In experimental game-playing situations, for example, many people will share money with a stranger even when there is nothing in it for them. This has led biologists to conclude that altruism is a part of human nature. What they cannot decide is how or why it evolved.

“People with a certain version of a gene called AVPR1 are more altruistic than the average”

According to Robert Trivers of Rutgers University in New Jersey, pure altruism is a mistake. He argues that natural selection favoured humans who were altruistic because in the small, close-knit groups in which our ancestors lived, altruists could expect reciprocity. However, in our globalised world where many of our interactions are with people we do not know and may never meet again, our altruistic tendencies are misguided: they are unlikely to be reciprocated and are therefore maladaptive (91av, 12 March 2005, p 33).

Others disagree. They accept that altruism cannot be a product of genetic evolution, but argue that ever since our ancestors began to shape their own environment through culture, we have evolved by a process of genetic and cultural co-evolution. As well as favouring traits that benefit individuals, this can also select traits that benefit one group over another – and that is how altruism evolved. Altruism is crucial for social cohesion. And groups that are more cohesive are more likely to survive in interactions with other groups.

At a mechanistic level, gene-culture co-evolution makes sense. There are clear social mechanisms that promote altruism: for example, fear of punishment, reputation building, ideas of fairness and inculcation by religious or authority figures. There are also indicators that altruism has biological roots. Brain imaging reveals that it stimulates the reward centres of our brains. What’s more, it would appear that people with a certain version of a gene called AVPR1 are more altruistic than the average. Their brains are more susceptible to the effects vasopressin, a feel-good hormone implicated in social bonding (). Of course some might argue that if random acts of kindness give us a mental buzz, then this is not pure altruism after all.

Read more: Ten mysteries of you