Scientists have revealed that the reason for most conflict in the world from war to football violence could be caused by the male sex drive.
A review of psychological research has concluded that men evolved to be aggressive towards 'outsiders', a tendency at the root of inter-tribal violence.
The researchers say it emerged through natural selection as a result of competition for mates, territory and status, and is seen in conflicts between nations as well as clashes involving rival gangs, football fans or religious groups.
"A solution to conflict?.?.?. remains elusive," said Professor Mark van Vugt, of Oxford University's Institute of Cognitive and Evolutionary Anthropology.
"One reason might be the difficulty we have in changing our mindset, which has evolved over thousands of years," he stated.
The findings support the 'male warrior hypothesis.'
The psychologists claim that in all cultures and throughout history, men have sought to get their way by initiating violence.
They prefer group-based hierarchies and are identified more strongly with their own groups than women.
At a basic level, such 'tribal' aggression helped men in a group to obtain more females, increasing their chances of reproduction.
"We see similar behaviour in chimpanzees. For example, the males continuously monitor the borders of their territory," said Prof van Vugt.
"If a female from another group comes along, she may be persuaded to emigrate to his group. When a male strays too far, however, he is likely to be brutally beaten and possibly killed," he explained.
The findings are published in the journal Philosophical Transactions of the Royal Society B.