How to tell if a man will commit? Check out his fingers

High up the list of must-haves for most women seeking a partner is commitment. But how can you tell if a man’s the sort to stick around?

Many of us learn from bitter experience that promises of commitment are easily broken. If only there was a reliable way of gauging a man’s propensity for devotion before starting up a relationship. Well, it turns out there might be, and the place to look is rather unusual. It’s his hands. And I’m not talking body language here, I’m talking digit ratio: that’s the relative length of his fingers.

If a man’s index finger is shorter than his ring finger, he’s more likely to be a short-term kinda guy.

This might sound like the sort of quack idea that’s regularly torn to shreds by Ben Goldacre in his Bad Science column, but it’s nothing to do with the life lines and fate lines beloved of fairground palmists. In fact, there’s a decent amount of scientific evidence that all kinds of behaviour and abilities can be predicted by the ratio of the second to fourth digits, or, as it’s also known, the 2D:4D ratio.

That’s because finger growth is influenced by the amount of testosterone you’re exposed in your mother’s womb. Males, for example, are exposed to more testosterone than females, which explains why men tend to have lower 2D:4D ratios than women. And 2D:4D not only differs between the sexes — there are also differences between individuals, regardless of their gender.

Sascha Schwarz and colleagues of Wuppertal University in Germany recently carried out a study to see if these differences might predict preferences for long- or short-term relationships. They predicted that, because testosterone can promote sexual behaviour, men who were exposed to more testosterone in the womb, and who therefore have shorter index fingers compared to their ring fingers, would be orientated more towards a short-term mating strategy.

In two studies, published recently in the journal Archives of Sexual Behavior, they confirmed this hypothesis. Men with male-typical digit ratios were orientated more towards short-term relationships, agreeing more strongly with statements such as “There is nothing to be said against having sex with a stranger” and “I want to have as many relationships as possible”.

The researchers didn’t find the same effect in women, which is unsurprising given that previous studies have shown women are more flexible than men in their relationship orientation. For example, women tend to be more pro-short-term relationships during the fertile phase of their menstrual cycle, around ovulation, and more pro-long-term relationships at other times.

Men’s digit ratio wasn’t associated with their preferences for long-term relationships, which is also unsurprising because digit ratio is influenced by testosterone, and long-term attachment is probably driven by other hormones, such as vasopressin and oxytocin—the family of natural chemicals that promote lactation and mother / child bonding.

So if you want to make sure your man is for life and not just for Christmas, you know what to put in his stocking. A massive bottle of vasopressin. Failing that, I always find a pair of socks is a good stand by.

Schwarz, S., Mustafić, M., Hassebrauck, M., & Jörg, J. (2011). Short- and long-term relationship orientation and 2D:4D finger-length ratio. Archives of Sexual Behavior, 40(3), 565–574. Read summary

The content of this post first appeared in the December 2010 episode of The Psychology of Attractiveness Podcast.

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