A man's ring finger may point the way to domestic bliss

Before you get too serious about a new boyfriend, you may want to make him show you his hands.

New research out of McGill University shows that men with shorter index fingers and longer ring fingers are nicer towards women. The researchers say exposure to certain hormones in the womb causes a man to develop a longer ring finger and affects his behavior as an adult.

"When with women, men with smaller ratios [between index and ring fingers] were more likely to listen attentively, smile and laugh, compromise or compliment the other person," Debbie Moskowitz, lead author and professor of psychology at McGill, said in a press release. These men also tend to have more children than their shorter ring-fingered counterparts.

The study, published in the journal Personality and Individual Differences, isn't the first to show a link between ring-finger length and adult male traits.

Previous research points to the digit ratio -- the length of the index finger divided by the ring-finger length -- as an indication of the amount of male hormones, mainly testosterone, that a fetus is exposed to in development. A smaller digit ratio means more male hormones, and the McGill study implies that this has an impact on how men behave and interact with women as adults.

"It is fascinating to see that moderate variations of hormones before birth can actually influence adult behavior in a selective way," said coauthor Simon Young, McGill emeritus professor in psychiatry.

The study spanned 20 days and asked 155 participants to fill out forms, checking off a list of behaviors they engaged in for every social interaction lasting five minutes or more. The scientists classified certain behaviors as agreeable or quarrelsome. They found that men with small digit ratios reported approximately one third more agreeable behaviors and approximately one third fewer quarrelsome behaviors than men with large digit ratios.

"Our research suggests they have more harmonious relationships with women; these behaviors support the formation and maintenance of relationships with women," said Moskowitz. "This might explain why they have more children on average."

The researchers said they did not find a statistically relevant link between digit ratios and dominant behaviors like competitiveness, and suggested more studies to look into that question.