Male sex drive is at the root of most conflict in the world, from football violence to world wars, scientists have claimed.
A review of psychological evidence concludes that men are shaped by evolution to be aggressive towards 'outsiders'.
The tendency, at the heart of all inter-tribal violence, emerged through natural selection as a result of competition for mates.
Today it can be seen in large-scale conflicts between nations as well as clashes involving rival gangs, football fans or religious groups, say the researchers.
Women, on the other hand, are said to have evolved to resolve conflicts peacefully.
Natural selection has programmed them to 'tend and befriend' to protect their offspring.
Professor Mark van Vugt, from the Institute for Cognitive and Evolutionary Anthropology at Oxford University, said: 'A solution to conflict, which is an all too common problem in societies today, remains elusive.
'One reason for this might be the difficulty we have in changing our mindset, which has evolved over thousands of years.
'Our review of the academic literature suggests that the human mind is shaped in a way that tends to perpetuate conflict with "outsiders".
'Our research finds that conflict between rival groups of men has presented opportunities to gain access to mates, territory and increased status.
'We believe this has resulted through natural selection in an evolved psychology amongst men to initiate and display acts of inter-group aggression.'
Better behaved: Researchers say natural selection has programmed women to 'tend and befriend' to protect their offspring
The findings, which support the so-called 'male warrior hypothesis', are published today in the journal Philosophical Transactions of the Royal Society B.
In all cultures and throughout history men rather than women have sought to get their way by initiating violence, the psychologists claim.
Men were more likely to demonstrate prejudice and discrimination against other men viewed as outsiders, according to the research.
They preferred group-based hierarchies and were 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,' said Prof van Vugt. 'For example, the males continuously monitor the borders of their territory.
'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.'
