A study released earlier this month relied on the "2D:4D" ratio to determine that57 percent of men are inclined to be promiscuous. Now, a second study says the same ratio—which makes use of the length of the index and ring fingers—can also indicate how nice men are to women.

The study, published in Personality and Individual Differences, notes that a lower ratio "indicates greater androgen exposure"; in less scientific-speak, it means the longer a man's ring finger compared to his index finger, the more male hormones (chief among them testosterone) he was exposed to in the womb.

As lead author Debbie Moskowitz explains in a McGill University press release, "When with women, men with smaller ratios were more likely to listen attentively, smile and laugh, compromise or compliment the other person." The results stemmed from 155 participants' self-reported behavior.

Over the course of 20 days, they selected which behaviors they exhibited in any social interaction of at least five minutes. The researchers mapped those behaviors as agreeable or quarrelsome, and discovered men with lower digit ratios reported roughly a third more agreeable behaviors with women, and also a third fewer quarrelsome ones.

The results went beyond the romantic: They held regardless of who the woman was, from a romantic partner to a co-worker. But in terms of the romantic, Moskowitz noted her findings may support previous research that also linked smaller ratios to having more kids.

"Our research suggests they have more harmonious relationships with women ... This might explain why they have more children on average." Somewhat incongruously though, the smaller-ratio men were the ones who fell into the potentially more promiscuous camp in the previous study.