03 April 2015

Finger Length Ratio

Welcome back. Today I’m going to tell you things about you. To do that I’ll need a number. Please do the following:
2D:4D Finger Length Ratio.
(Photo from multiple websites)

Find a ruler and measure the length of your index finger (aka forefinger), base to tip on the palm side. Label that measurement “2D,” for second digit. (The thumb is 1D.) Now, measure the length of your ring finger. Label that “4D,” for fourth digit. Finally, do a little math. Calculate the ratio 2D:4D by dividing the length of your index finger, 2D, by the length of your ring finger, 4D.

You’ll be amazed how much your 2D:4D finger length ratio conveys about you.

Digit Ratio and Agreeableness

When I first saw that a recent study found men’s 2D:4D ratios signaled the men’s agreeableness with women, I had serious reservations even though the work came from the highly respected McGill University in Montreal.

The McGill researchers had 155 volunteers (78 men, 77 women) spend three weeks completing forms with a checklist of "agreeable" or "quarrelsome" behaviors for every social interaction that lasted at least five minutes with someone of the opposite sex.

Men with smaller 2D:4D ratios (index finger shorter than ring finger) were significantly more agreeable and less quarrelsome toward women than toward men. Those men checked on the order of one-third more agreeable behaviors toward women and one-third fewer quarrelsome behaviors. Women, in contrast, showed no relationship between their finger length ratio and behavior.

Cause for Differences?

Was this phrenology revisited? (Phrenology, you’ll recall, is the pseudoscience that focused primarily on measurements of the human skull to gauge an individual’s strengths and weaknesses.) Nope, it’s real science and the finger length ratio is far from being a new parameter.

Ratio differences were reported in scientific papers in the final quarter of the 19th century--for example, that men and women typically have shorter index fingers than ring fingers, but men’s are generally shorter. If I got it right, however, it took another century before anyone reported a relationship between the ratio and behavior and offered an explanation for why.

A 1983 study of 985 women by a researcher at King’s College in London found that women with 2D:4D ratios less than 1 (index finger shorter) were more likely to describe themselves as “assertive and competitive” than women with 2D:4D ratios greater than 1 (index finger longer). The researcher suggested that the finger length and behavioral differences could reflect the simultaneous effect of prenatal sex hormones on body and brain.

And apparently that’s more or less still the accepted cause. The 2D:4D ratio, like other adult phenotypes, is affected by androgens, such as testosterone, while developing in the uterus. The ratio is thus a measure, albeit rough, for the level of prenatal androgen exposure.

Wrap Up

Over the years, various studies have related 2D:4D ratios with behaviors, health and sexuality. While not all studies had positive results, among many that did are relationships with academic performance, rate of ADHD, anxiety, leadership, sensory perception, risk of prostate cancer, heart disease and alcohol dependency, sperm count and penile length.

The relationships seem better expressed by the right than left hand, suggesting that more than prenatal androgen exposure is involved; and more relationships are men only (not just penile length) than female only.

Overall, it’s an interesting topic with a broad potential reach. Thanks for stopping by.


McGill University study in Personality and Individual Differences journal:
Articles on McGill and related studies on Science Daily and LiveScience websites:
King’s College study in Personality and Individual Differences journal:
Discussion of topic on Wikipedia:

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