Nice guy or a jerk? Check his hands
Nice guys and jerks can be recognised at a glance by looking at men's hands, new research suggests.
Scientists have discovered that men who are polite, attentive and considerate to women generally have ring fingers relatively longer than their index fingers.
Those with fingers closer to the same length turned out to be more quarrelsome, stubborn and rude.
Previous research has shown that "digit ratio" - defined as ring finger length divided by index finger length - is affected by hormone exposure in the womb.
The smaller the ratio, the more an unborn baby has been exposed to male hormones, chiefly testosterone.
This has an impact on the way adult men behave towards women, according to scientists at McGill University in Canada.
Lead researcher and psychiatrist Professor Debbie Moskowitz said: "When with women, men with smaller ratios were more likely to listen attentively, smile and laugh, compromise, or compliment the other person."
They acted that way both in sexual relationships and also with female friends or colleagues, she said.
The "nice guys" with smaller ratios were also less quarrelsome with women than they were with men. Men with larger ratios - whose ring and index fingers were nearer the same length - were equally likely to pick an argument with both.
During the 20-day study, 155 participants filled out forms for every social interaction that lasted five minutes or more and checked off a list of behaviours they engaged in.
Based on previous work, the scientists classified the behaviours as "agreeable" or "quarrelsome".
Men with small digit ratios reported roughly a third more agreeable behaviours and a third fewer quarrelsome behaviours than men with large ratios.
A previous study has found that men with smaller digit ratios have more children. The new findings suggest one reason for this might be that they are less likely to break up with women or end up dumped.
"Our research suggests they have more harmonious relationships with women," said Prof Moskowitz. "These behaviours support the formation and maintenance of relationships with women. This might explain why they have more children on average."
The scientists were surprised to find no statistically relevant link between dominant behaviours and digit ratios.
They suggested future research could study specific situations where male dominance varies, such as competitive situations with other men.
The findings were published in the journal Personality and Individual Differences.