London: Men only have to believe that they have bested another man in competition to get an inflated sense of their own value as a sexual prospect, and indulge in promiscuous behaviour.
Scientists from the University of Cambridge in the UK found that this hormonal and psychological shift made men more inclined to approach new potential partners.
The research team measured hormone levels, as well as self-perceived attractiveness and confidence in approaching women, in 38 men in their twenties before and after competing in head-to-head battles on rowing machines.
The competitions in the study were rigged to randomly declare the winner, regardless of who was the stronger rower.
The study, published in the journal Human Nature, shows that just being convinced you have won, or indeed lost, is enough to cause male hormonal fluctuations that can influence sexual behaviour.
The body attempts to take advantage of this apparent status improvement by inducing chemical and consequently behavioural changes that promote a "short-term" approach to reproductive success, researchers said. This may mean more sex with new and different partners.
"Victory in a rowing contest strongly implies the possession of greater physical strength than the opponent, a trait found to be valued by women in our evolutionary past when choosing a mate," said Danny Longman, from Cambridge.
He took saliva samples to test hormone levels before and after the races. A number of psychological questionnaires were also administered, designed to gauge self-esteem, 'sociosexuality' (willingness to engage in casual sex), 'self-perceived mate value' and mating behaviour (eg the likelihood of approaching attractive women).
Crucially, researchers then manipulated the results of the races.
The men who believed they had won received an average testosterone increase of 4.92 per cent, while those convinced they had lost dropped by an average of 7.24 per cent.
Overall, men who thought they were winners had testosterone levels 14.46 per cent higher their deflated opponents.
The men who thought they had lost showed no difference in their perceived value as a mate or confidence approaching women.
However, the men who felt like winners had a 'self-perceived mate value' that was 6.53 per cent higher, on average, than their rivals, and were 11.29 per cent more likely to approach attractive women in an effort to instigate sexual relations.
"The endocrine system that controls hormones is responsive to situational changes. Previous research has shown that testosterone is lower when men are in a committed relationship, or have children, to promote long-term mating strategies," said Longman.
Male social status has less to do with physical strength in many modern societies, and Longman would be curious to see if similar results arise from intellectual challenges more familiar to the office-based culture many men now inhabit. There is always the issue of free will, however.