Ladies, stop judging a man by his shoes, check his fingers instead!
Men with short index fingers and long ring fingers are on average nicer towards women and less quarrelsome, according to a new study.
Researchers at McGill University, Canada, said this phenomenon stems from the hormones these men have been exposed to in their mother's womb.
Men's index fingers are generally shorter than their ring fingers. The difference is less pronounced in women.
Previous research has found that digit ratio - defined as the second digit length divided by the fourth digit length - is an indication of the amount of male hormones, chiefly testosterone, someone has been exposed to as a foetus: the smaller the ratio, the more male hormones.
The McGill study suggests that this has an impact on how adult men behave, especially with women.
"It is fascinating to see that moderate variations of hormones before birth can actually influence adult behaviour in a selective way," said Simon Young, a McGill Emeritus Professor in Psychiatry and coauthor of the study.
The study is the first to highlight how finger lengths affect behaviour differently depending on the sex of the person you are interacting with.
"When with women, men with smaller ratios were more likely to listen attentively, smile and laugh, compromise or compliment the other person," said Debbie Moskowitz, lead author and Professor of Psychology at McGill.
They acted that way in sexual relationships, but also with female friends or colleagues. These men were also less quarrelsome with women than with men, whereas the men with larger ratios were equally quarrelsome with both.
For women though, digit ratio variation did not seem to predict how they behaved, the researchers said.
In the study, for 20 days, 155 participants filled out forms for every social interaction that lasted 5 minutes or more, and checked off a list of behaviours they engaged in.
Based on prior work, the scientists classified the behaviours as agreeable or quarrelsome.
Men with small digit ratios reported approximately a third more agreeable behaviours and approximately a third fewer quarrelsome behaviours than men with large digit ratios.
A previous study had found that men with smaller digit ratios have more children.
"Our research suggests they have more harmonious relationships with women; these behaviours support the formation and maintenance of relationships with women. This might explain why they have more children on average," Moskowitz said.
The study was published in the journal Personality and Individual Differences.
