Can you judge a person by his fingers? If that person’s a men, yes you can, some scientists would agree. Researchers at McGill University found that men with short index fingers and long ring fingers are on average nicer to women. Not entirely a correlative study, the findings seem to have weight as previously a link was found between high levels of testosterone in the womb and shorter index finger relative to the ring finger. You can stop watching your fingers now.

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Generally, index fingers are shorter than ring fingers  in men. This difference is less pronounced in women. The ratio between the second digit length and the fourth digit length   is an indication of the amount of male hormones, chiefly testosterone, someone has been exposed to as a fetus: the smaller the ratio, the more male hormones.

“It is fascinating to see that moderate variations of hormones before birth can actually influence adult behaviour in a selective way,” says Simon Young, a McGill Emeritus Professor in Psychiatry and coauthor of the study.

During 20-day-long study, 155 participants were asked to log in any social interaction that lasted more than 5 minutes and check a list of behaviours. These could be 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.

“When with women, men with smaller ratios were more likely to listen attentively, smile and laugh, compromise or compliment the other person,” says Debbie Moskowitz, lead author and Professor of Psychology at McGill.

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 report.

This might serve to explain why men with shorter index figures have more children, the researchers write in the journal Personality and Individual Differences.

“Our research suggests they have more harmonious relationships with women; these behaviors support the formation and maintenance of relationships with women,” Moskowitz says.