A new study has shown that kind-hearted people are naturally generous.
A research team led by Masahiko Haruno of Tamagawa University in Tokyo, Japan has shown that generosity - or the desire for fairness - appears to be automatic and arises from activation in a brain area that controls intuition and emotion.
They define "prosocial" people as those who prefer to share and share alike, and "individualists" as those who are primarily concerned with maximising their own gain.
During the study, Haruno along with colleagues from University College London conducted MRI scans of the brains of 25 prosocial people and 14 individualists and rated their preference for a series of money distributions between themselves and a hypothetical other person.
They found that the prosocial group preferred even splits while the individualists favoured distributions where they got the most money.
And the only brain region that differed in activity between the two groups was the amygdala.
The study showed that when presented with unfair money distributions the activity in the amygdala increased significantly in prosocial people but not in the individualists.
"And the more they disliked the split, the more activity you saw in this region," New Scientist quoted Frith as saying.
"The amygdala tends to respond automatically, without thought, or even without awareness," Frith added.
In another test to understand if the prosocial aversion to unfairness was automatic, the researchers gave the participants a memory task to complete at the same time as they rated the splits.
They found that the prosocials' brains still reacted to the unfair distributions, even when the parts of their brain responsible for deliberative processes were taken up by other tasks, suggesting they were not suppressing selfish desires.
So far, all behavioural and fMRI experiments confirm that prosocials are intrinsically motivated to cooperate," said Carolyn Declerck, a neuroeconomist at the University of Antwerp, Belgium.
The study appears in journal Nature Neuroscience.