Fingered

Posted on Thursday 11 November 2004 to unknown


Non-geek

While we're on the subject of fingers, allow me to point out [sic] some interesting dactylic research.

Men who work in the so-called "hard" sciences, that is, sciences which are mathematical and precise (physics etc.), generally have hands that differ from the general male population. Specifically, they tend to have index fingers which are at least as long or slightly longer than their ring fingers. The wider male population, on the other hand [sic], tend to have ring fingers which are longer than their index fingers.

This same pattern is also reflected amongst computer programmers where finger ratio has been correlated to test scores.

While most of us have, at one time or another, had our palms scrutinised for lines and creases by someone with an interest in palmistry and fortune telling, I'm pretty sure not a lot of people have given much thought to the relative lengths of their fingers. Surprisingly, we can learn quite a bit about our destinies by examining them.

How much precisely? Well, cross my palm with silver1 and let me tell ye.

1 - or you could try clicking one of those Google Ads below.

It's been known for over a century that male and female hands differ noticeably in terms of their relative finger length. Men on average, as I mentioned earlier, tend to have longer ring fingers while women are more likely to have index and ring fingers of the same length. We're not talking here about big differences, only a few percent, but even such slight variations can be revealing.



The ratio of the length of an individual's index finger to their ring finger remains remarkably constant throughout the whole of life and is established very early on, while still a foetus in the womb. Finger length development is strongly influenced by the levels various hormones and different fingers are influenced by different hormones. The growth of the index finger is most sensitive to the level of oestrogen while the growth of the ring finger is most sensitive to the level of testosterone. It has been discovered in recent years that the ratio between the lengths of these fingers serves as a surprisingly reliable indicator of the relative levels of these hormones during pregnancy.

For males a longer index finger (i.e. a higher oestrogen to testosterone ratio) is linked to enhanced spacial skills and this in turn can help them do maths and science. Longer ring fingers, conversely, are linked with greater social and communication skills.

Furthermore, males with longer index fingers tend to have fewer children, run a higher risk of early heart disease and have a higher than average likelihood of having relatives with dyslexia. Males with longer ring fingers are generally more assertive and aggressive in their behaviour, have a greater aptitude for music, have a higher fertility and, if the youngest out of a family of boys, a higher than average proclivity towards homosexuality. Quite long ring fingers may also be indicative of autism or Asperger's Syndrome.

Finger length ratios in women also indicate a number of things. Let me start by offering the chaps reading this an even better reason to check a woman's ring finger before asking her out.

Women with index fingers equal or longer than their ring fingers tend to be more fertile but they also run a greater risk of getting breast cancer. Women with longer ring fingers tend to be more assertive and aggressive in their behaviour and have a higher than average proclivity towards homosexuality.

One of the questions that has not yet been adequately addressed by this kind of research is that if males with index fingers equal in length to their ring fingers (i.e. having an oestrogen to testosterone ratio comparable with that of women) tend to be good at the "hard" sciences, why aren't there more women scientists and mathematicians? The answers offered, predictably enough, range from biological differences to social prejudice. One observation that has been made, however, is that women in the social sciences tend to have longer ring fingers and therefore have hormone ratios similar to those of their male collegues.

See also: Book Review Digit Ratio: A Pointer to Fertility, Behavior and Health by John T. Manning



UPDATE: Mark Liberman at Language Log makes some very interesting and important comments about this post. His key point is that these findings about finger length ratios should be used with extreme caution and should not be used to infer anything in an individual person't case. I'll just quote it at length:

What (little) know about the stuff on sex hormones, finger lengths and cognitive profiles is from the work of Doreen Kimura (her home page is here). The serious part is the putative relation between sex hormones and cognitive skills; a good summary of her perspective is "Sex Hormones Influence Human Cognitive Pattern", Neuroendocrinology Letters 2002; 23(Suppl. 4):67-77. The finger length business is not entirely a curiosity, since to the extent that it really reflects prenatal sex hormone levels, it serves as a somatic marker that can interestingly be correlated with all sorts of things, including adult sexual orientation as well as various test results, life choices and so on.

The jargon for the difference is 2D:4D ratio ("second digit to fourth digit ratio"). It's easy to measure -- though there is surely a real possibility for observer bias to play a role in the measurements -- and the fact that collecting data is so simple strikes me as both an opportunity and a danger. It's easy to do little studies of this that and the other, and for people to do self-evaluations from which they (or their schoolmates) may draw invidious conclusions. In the (few) cases where I've looked at the data in detail, I find results like those in Q. Rahman and G.D. Wilson, "Sexual orientation and the 2nd to 4th finger length ratio", Psychoneuroendocrinology 28:3, April 2003, 228-303, where the differences were highly significant in the statistical analysis:

For right-hand ratios, there was a significant effect of sexual orientation (F=24.237, df=1, 239 P=0.000); homosexuals having lower right-hand 2D:4D ratios than heterosexuals. There were no significant effects of gender (F=0.115, df=1, 239, P=0.735), no significant interaction (F=1.684, df=1, 239, P=0.196) and no significant effects of the covariates (all Ps>0.10). Overall, the difference between homosexuals and heterosexuals constituted a moderate to large effect.

However, these highly significant differences in the mean value were nevertheless rather small, as a proportion of the means, and also relative to the variance:


 Right-hand
2D:3D ratio
(mean)		 Standard deviation
Heterosexual males
0.97
0.03
Heterosexual females
0.98
0.02
Homosexual males
0.96
0.03
Homosexual females
0.95
0.02

In other words, the mean values for homosexuals and heterosexuals differed in their sample of males by 1 part in 100, and in their sample of females by 3 parts in 100; while the standard deviations of the measurements within each subgroup were 2 to 3 parts in 100. It bothers me that the newspapers (and even science magazines) who report this kind of stuff never try to explain this aspect of the results, which could easily be gotten across with histograms, or with scatter plots when the dependent variable is something like programming skill. The excuse for not doing this, I've been told, is that readers would be confused by the details; but an equally strong reason, I suspect, is that such explanations would undermine the apparently spectacular results ("you can tell someone's sexual orientation from their finger lengths!") with a small dose of reality ("no you can't, not with any accuracy in individual cases; the experiment showed only that you can distinguish a set of 60 homosexuals from a set of 60 heterosexuals on the basis of this measurement").

One could (and should) take the same care in presenting the results about demonstrated sex differences in cognitive skills, which are often of a similar nature.