Our physical characteristics say all kinds of interesting things about us. For instance, our height may reveal something about our interest in being a leader (Are You Sure…?) and how we use our dominant hand may indicate something about our political ideology (On One Hand...).

It turns out that the length of your index finger relative to your other fingers may also have political implications.

What?!

I know, this sounds crazy. But let’s step back and look at what the “finger ratios” may be biomarkers for. A number of scientists argue that the ratio of the length of the second digit (index finger) to the length of the fourth digit (ring finger), known as the “2D:4D ratio,” is an indicator of prenatal exposure to testosterone

As the argument goes, the larger one’s in utero exposure to testosterone is the smaller one’s later 2D:4D ratio is (i.e., index finger length ÷ ring finger length). For a very rough guide, according to one study the average adult male 2D:4D ratio for the right hand is 0.95, while the average adult female ratio is 0.97 (with a standard deviation of about 0.03 for both sexes—sorry, I’m a scientist, I can’t help reporting the numbers). It’s important to emphasize this is a very imprecise benchmark, because the ratio varies more between races and cultures than it does between the sexes. 

So what?

Although 2D:4D effects are not universal and the exact causal mechanisms have not been identified, a great deal of research suggests something more than chance is going on. Research has shown that prenatal testosterone is related to adult aggressiveness in both humans and non-human primates. One recent study indicates both men and women with smaller 2D:4D ratios (suggesting greater prenatal testosterone exposure) self-report greater verbal aggressiveness. Another recent study associates 2D:4D with sports-related mental toughness, aptitude, and achievement. Finally, research co-authored by fellow PT blogger Gad Saad (Homo Consumericus) finds that men, but not women, with smaller finger ratios take more risk in certain recreational, social, and financial situations.

Clearly, this finger ratio may be indicative of political preferences. For example, one study found that low, more masculine 2D:4D predicted greater unprovoked attack in a simulated war game, in particular in men. It’s very easy following these and the results of some of the non-political research to begin wondering whether 2D:4D could be a useful bio-indicator for differences in political ideology in general and in policy preferences specifically such as crime policy and the management of security net programs like Social Security and Medicare.

If this research continues to hold true, be careful talking with your hands. You’ll have to worry about one more physical characteristic betraying your thoughts.

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For more information on the war game study, see: McIntyre et al. 2007. “Finger length ratio (2D:4D) and sex differences in aggression during a simulated war game.” Personality and Individual Dierences 42: 755-764.

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