New research carried out in Northern Ireland has found that people who find themselves in a situation of conflict with other groups are less likely to help individuals from outside their own group.
The study, conducted by researchers from University College London, found no evidence that Catholics or Protestants in Northern Ireland were less likely to help people within their own group as a result of their exposure to sectarian violence.
For some time, it has been thought that humans have learned to cooperate because of the competitive advantage this gives them over groups made up of selfish individuals.
More recently, however, scientists have theorised that altruism within groups co-evolves with hostility towards other groups, because it contributes to the success of the inwardly altruistic group.
The researchers set out to test this hypothesis, by studying the behaviour of groups on both sides of the sectarian divide in Northern Ireland.
They conducted a number of field experiments, including an effort to collect donations for either a Catholic or Protestant school in the local area, or a neutral charity.
They also ran a lost letter experiment, where 832 stamped letters addressed to fictional Catholic, Protestant and cancer charities, were dropped on the ground in 22 areas, to see if they would be picked up and posted on.
Their results, published in the journal Proceedings of the Royal Society B, found that the level of donations made by people to schools outside of their religious group were less than those made to schools they were religiously affiliated with.
In particular, individuals who had experienced greater sectarian violence and felt most threatened by the other groups were less likely to donate money to a so-called "out-group" school.
Likewise, fewer letters were returned to the fictional charities of the so-called "out-group", particularly in neighbourhoods with higher perceived threat levels.
However, the results also show that cooperation within groups was not influenced by exposure to sectarian conflict.
Instead, the researchers found that socio-economic status was the main determinant of group cooperation, with wealthy and highly-educated people more likely to help others.