Psychologists in Canada have finally proved what women have long suspected – men really are irrational enough to risk entire kingdoms to catch sight of a beautiful face.

Biologists have long known that animals prefer immediate rewards to greater ones in the future. This process, known as “discounting the future”, is found in humans too and is fundamental to many economic models.

Resources have a value to individuals that changes through time. For example, immediately available cash is generally worth more than the same amount would be in the future. But greater amounts of money in the future would be worth waiting for under so-called ‘rational’ discounting.

But some people, such as drug addicts, show ‘irrational’ discounting. For example, preferring a small amount of heroin today rather than a greater amount in the future.


Margo Wilson and Martin Daly of McMaster University in Hamilton, Canada decided to investigate discounting behaviour and see if it varied with sexual mood.

Male students, when shown pictures of pretty women, were more likely to opt for short-term economic gain than wait for a better reward in the future.

Sexual opportunity

Both male and female students at McMaster University were shown pictures of the opposite sex of varying attractiveness taken from the website ‘Hot or Not’. The 209 students were then offered the chance to win a reward. They could either accept a cheque for between $15 and $35 tomorrow or one for $50-$75 at a variable point in the future.

Wilson and Daly found that male students shown the pictures of averagely attractive women showed exponential discounting of the future value of the reward. This indicated that they had made a rational decision. When male students were shown pictures of pretty women, they discounted the future value of the reward in an “irrational” way – they would opt for the smaller amount of money available the next day rather than wait for a much bigger reward.

Women, by contrast, made equally rational decisions whether they had been shown pictures of handsome men or those of average attractiveness.

“We have not elucidated the psychological mechanisms mediating our results,” says Margo Wilson. “But we hypothesise that viewing pictures of pretty women was mildly arousing, activating neural mechanisms associated with cues of sexual opportunity.”

Tommaso Pizzari, an evolutionary biologist at Leeds University, offers another possible explanation: “If there’s the prospect of getting a very attractive partner it may pay a man to take more risks than if an average partner was available.”

He told New Scientist: “If this is a response to sexual selection then you would expect men who are less attractive to take more risks. If you have many attractive potential partners then it does not pay to take risks. If you are less attractive, with few potential partners, then it pays to take risks.”

Journal reference: Biology Letters (DOI 10.1098/rsbl.2003.0134)