The study, conducted by researchers from UCL and Oxford University and funded by the Wellcome Trust, is the first to experimentally compare how much pain people were willing to anonymously inflict on themselves or strangers in exchange for money.

The results showed that people would sacrifice an average of 20p per shock to prevent shocks to themselves and 40p per shock to prevent shocks to others.

Similarly, people would need an average 30p incentive per shock to increase shocks to themselves and 50p per shock to increase shocks to others.

The findings provide a surprisingly optimistic view of human nature, in stark contrast with previous economic studies claiming people fundamentally care about their own interests over those of other people.

Understanding how people balance financial gains against the suffering of others could help to explain how policymakers and business leaders make spending decisions, for example on policies to improve the welfare of citizens or employees.

We have shown that when it comes to harm, most people put others before themselves. Dr Molly Crockett

The research also provides insight into clinical disorders characterised by a lack of empathy, such as psychopathy. People with more psychopathic traits were more likely to harm both others and themselves, suggesting antisocial behaviour could result from a general insensitivity to harm. A better understanding of how people evaluate the suffering of others relative to themselves, and how that differs in people with antisocial tendencies, could lead to more effective treatments.

The research involving 80 pairs of adults is published in the journal Proceedings of the National Academy of Sciences.

In the experiment, the 160 participants were randomly assigned to the roles of decider and receiver without knowing who they were paired with.

All participants were given mildly painful electric shocks matched to their pain threshold so that the intensity was not intolerable. Deciders were explicitly told that shocks to receivers would be at the receiver’s own pain threshold.

Deciders went into a room alone with a computer terminal, and each took part in 150–160 trials. For each trial, they had to choose between different amounts of money for different numbers of shocks, up to a maximum 20 shocks and £20 per trial. For example, they might be offered a choice of 7 shocks for £10 or 10 shocks for £15. Half of the decisions related to shocks for themselves and half to shocks for the receiver, but in all cases the deciders would get the money.

At the end of the session, one of the chosen trial results would be implemented so that the decider or receiver received the shocks and the decider received the profits. As such, their decisions had real consequences. Deciders knew that their decisions would be kept secret so that fear of judgement or retaliation would not skew the results.

At the end of the study, volunteers could donate a proportion of their winnings to charity. Although the people in this study were highly altruistic in terms of sparing others from pain, they only donated an average 20% of their winnings to charity, consistent with past research. This comparatively selfish behaviour shows that altruism is highly context-dependent.

'These results contradict not just classical assumptions of human self-interest, but also more modern views of altruism' says lead author Dr Molly Crockett, who conducted the study at UCL and is now in the Department of Experimental Psychology at Oxford University. 'Recent theories claim people value others’ interests to some extent, but never more than their own. We have shown that when it comes to harm, most people put others before themselves. People would rather profit from their own pain than from someone else's.

'We also timed volunteers' decisions, and found that they hesitated longer when the decision involved harming another person. The most altruistic subjects in our study took the longest to decide for others, suggesting that they may have been making moral calculations.'

She adds: 'Although people in this study were highly altruistic in terms of sparing others from pain, they were much more selfish when given the chance to donate money to charity. Exchanging money seems to bring out the worst in people who might otherwise selflessly help others avoid suffering, if given the opportunity.'