Painting depicting the story of the Good Samaritan

One for all, all for one?

If natural selection favours survival of the fittest, and genes are selfish, why do we ever help one another?

In the parable of the Good Samaritan, a man is robbed and left by the side of a road. Two travellers pass by on the other side, but a Samaritan stops and offers help.

I’d lay down my life for two brothers or eight cousins.

The parable illustrates the human ideal of altruism – helping others without expecting any benefit in return. But if our genes are only interested in making more copies of themselves, why would they cause us to behave like this? Why would natural selection favour people who helped others rather than people who looked after only themselves?

An early influential idea was that animals preferentially help their relatives, who share some of their genes. The more closely related they are, the more likely they would be to collaborate.

Kin selection suggested that genes supporting the survival of relatives could be favoured, even if they imposed a personal survival disadvantage. As J B S Haldane put it: “I’d lay down my life for two brothers or eight cousins.”

And there is evidence in nature, particularly social insects, that animals’ altruism varies with relatedness. But kin selection cannot be the complete story. Altruism, particularly in humans, goes beyond just family members.

What seems to be important is that social coordination and help for others is, in the long run, more successful. So mechanisms may evolve that lead to altruistic behaviour within a species because the long-term benefits outweigh the short-term advantage of selfishness.

How might that work in humans? One line of thought is that of ‘altruistic punishment’ – that there are policers of cooperative behaviour that enforce fair play. Anyone who transgresses a social norm is punished. This sort of behaviour can be seen in game theory studies, which explore people’s altruistic or selfish decision-making in various scenarios.

Another approach is to use mathematical models to analyse the spread of genes assuming particular types of behaviour in a population. This has shown that strategies such as indirect reciprocity – ‘I’ll scratch your back because I know someone will scratch mine’ – are successful.

Cooperation and altruism have been central to the success of human beings and remain essential for coherent, stable societies today. Scientifically, why we started acting together remains only partly clear.

Lead image:

Ted/Flickr CC BY NC


Questions for discussion

  • Do you think humans are naturally altruistic or only out for themselves?

About this resource

This resource was first published in ‘Evolution’ in January 2007 and reviewed and updated in December 2014.

Genetics and genomics, Ecology and environment, Psychology
Education levels:
16–19, Continuing professional development