Or at least, irrational.
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.
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.