• You are on a first date. You're both enjoying your meal and having a good conversation. You are really getting interested in this person. On the way back from the restaurant, he or she takes your hands, clearly a romantic gesture. But then he takes a ruler from his pocket and starts measuring your fingers, one by one.
  • You are interviewing for a management job. At one point, you are asked to present both your hands and someone comes in to measure up the length of your digits, especially your index and ring finger.

These sound like implausible scenarios, and yet the science of hand reading is moving fast and it is not entirely inconceivable that it will be a routine part of job interviews, or first dates, sometime in the future.

What do your digits tell about your personality?

What researchers are particularly interested in is the ratio between the lengths of your index finger versus your ring finger—the 2D:4D ratio. This ratio is a record of how much you were exposed to androgens such as testosterone, the male sex hormone, as a developing fetus in the womb. In other words, this digit ratio gives an indication of how masculinized both your body and your brain is. The lower the 2D:4D ratio—in other words, the longer your ring finger compared to the pointer—the more masculine you supposedly are.

You might want to try this at home but be warned: It is not easy to estimate this with the naked eye; researchers use a scanner to scan the hands and calculate the 2D:4D ratio precisely.

So what could this ratio reveal about you? Given that it is an indication of how masculine you are, men have a relatively longer ring finger (compared to the pointer) than women. Another fairly consistent finding is that it reveals something about your sexual orientation. Gay women have relatively low (more masculine) 2D:4D ratios compared to straight women. Gay men have a relatively high (more feminine) 2D:4D ratio. This suggests that sexual orientation is determined well before one's birth.1

Digit ratios have also been linked to a range of other traits such as voice pitch, spatial ability, physical prowess, and status and dominance but the correlations are not always very strong and these effects need replication.

In a recent study in the journal Aggressive Behavior, Dutch and Spanish scientists find that among men a lower 2D:4D ratio is related to a more aggressive, dominating personality.2 They first scanned the left and right hands of the male participants and then averaged the 2D:4D’s of both hands (hands are not identical). They then completed an aggressive dominance scale with items such as “When people are annoying me, I put them in their place” and “I quickly feel aggressive with people.” The more masculine 2D:4D’s scored higher on this scale. Digit ratios however were unrelated to any measure of social dominance or leadership. So, on items such as ”I have no problem talking in front of a group” or “People turn to me for decisions” there was no difference between the more masculine versus feminine digit ratios.

A more complex finding on digit ratios was published recently in the prestigious journal Nature. A research team in the Netherlands (which I was part of) conducted a study, where we looked at the effects of administering testosterone—via the mouth—on social cooperation. There was no straightforward effect of testosterone on social cooperation. Yet the effect is moderated by digit ratios. Only the more feminine digit ratios responded to testosterone by cooperating more with other people.

This shows that a boost in testosterone might not always produce more dominant or aggressive behavior. In fact, it will have the opposite effect for people with a higher (more feminine) digit ratio whi become more friendly.

So, if you are interested in someone romantically or would like to hire them as a future employee you could look them in the eyes to find out about their personality. Alternatively, and perhaps even better, ask them to send photocopies of their hands.

1 Putz, Gaulin, Sporter, & McBurney, (2004). Sex hormones and finger length: what does 2D:4D indicate. Evolution and Human Behavior, 25, 182-199.

2. Van Der Meij, Almela, Buunk, Dubbs, & Salvador (2012). 2D:4D in men is related to aggressive dominance but not sociable dominance. Aggressive Behavior, 38, 208-212.

3. Van Honk, Montoya, Bos, Van Vugt, & Terburg (2012). New evidence on testosterone and cooperation. Nature, 485, E4-5.

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