The new palmistry

I am a gorgeous hunk of virile manhood. How do I know? I looked at my fingers.

Research has shown that men whose ring finger on their right hand is longer than their index finger are regarded as better looking by women, possibly because their faces are more symmetrical.

There is no link, however, between this finger length and how alluring women find a man's voice or his body odour, the study found.

Guys, you may be looking at my picture on the sidebar and thinking there must be something wrong here…but no, I assure you, my right ring finger is distinctly longer than my right index finger, and I will waggle that in your face and tell you to ignore the schlubby, hairy, homely middle-aged guy attached to that hand — the fingers don't lie.

Right now I know a lot of you fellows are staring at your hand, and some of you are noticing that you have a long index finger, a sure sign that you are a hideous beast, unlike me. And others have nice long ring fingers, and you get to join me in my club of attractive manly men, no matter what the rest of your body looks like. We'll get together and make the ladies swoon.

Except, well…I've been looking at some of the data, and I'm distinctly unimpressed.

It's not the idea that digit ratios vary, though: that looks to be well established, with observations first made in the 19th century that men have relatively longer ring fingers, while women have relatively longer index fingers. There does seem to be an entirely plausible (but small) side-effect of testosterone/estrogen on digit development. There is even some rather noisy looking data that suggests that we can use digit length ratios as a proxy for embryonic testosterone/estrogen exposure.

The problem, unfortunately, is that there seems to be a little industry of scientific palmists who are busily cross-correlating these digit ratios with just about anything, and I think they are drifting off into measuring random noise. It's amazing what can get published in respectable journals, and subsequently get loads of attention from the press. Look at the methods for this study of attractiveness, for instance.

The team studied 49 Caucasian men aged between 18 and 33 years of age. They measured their finger ratio, got them to recite into a voice recorder, took a photograph of them with a neutral expression and got the non-smokers to wear cotton pads under their armpits for a day. The men were then evaluated for attractiveness, facial symmetry and masculinity by 84 women, and the results are published in the Proceedings of the Royal Society B.

Wow. Tiny little sample size, probably drawn from the usual limited population of college students, one straightforward objective measure (the digit ratio), and a subjective evaluation…and from this the authors try to infer a general rule. And sometimes they get a positive correlation with one thing, and no correlations with other things.

This is not only rather uninteresting, it's also not very reliable. But it's easy to do!

But wait, you might say, statistics is a powerful tool, and maybe those correlations are awesomely solid. This could be, so I went looking for papers that showed some of the data, so I could get a feel for how robust these effects were. Here, for example is a chart comparing number of the number of children to the ratio of index finger length to ring finger length (2D:4D ratio) for English men, where we'd expect low ratios to be a consequence of higher testosterone and therefore more virility, and for English women, where we'd expect a reversal, because fertile womanly women would of course have more estrogen. And it works!

Look at the slopes of those lines, and they actually fit the prediction. But then…look at the actual data points, and I think you can see that knowing the length of the fingers of any individual tells you absolutely nothing about how many children they have. You can guess why: it's because there are a great many factors that influence how fecund you are, and small variations in hormones are only going to be a tiny component of such decisions.

You may also notice the outliers. Look at that man with most womanly hands of the entire group, having a 2D:4D ratio of 1.1 — he also has the second largest brood of the whole sample, with 5 kids. And the woman with man-hands with ratio somewhere around 0.87? Four kids.

It's also a good thing that these data are collected in two separate graphs, because if you put the men and the women on the same chart, they'd overlap so much that you wouldn't be able to tell them apart. While the sex difference may have been documented since the 19th century, it's clearly not a big and obvious difference, and the overlap between the sexes is huge.

Or how about these data?

That's the splat you get when you compare 2D:4D ratio in women against another classic magic number associated with attractiveness, the waist-hip ratio. A correlation emerges out of that mess, too, and it turns out that more estrogen exposure (as indirectly measured by looking at digit lengths) is correlated with relatively thicker waists. Sort of. I guess. Yeah, it's statistics all right.

How these sorts of data are interpreted is to see them as suggesting the presence of sexually anatagonistic genes, that is, genes that respond to high testosterone with expression patterns that are beneficial to males, and genes that respond to high estrogen with expression that favorably biases morphology towards typically female variants. I can believe that such phenomena exist, and that doesn't bother me in the slightest; what does, though, is this I've-got-a-hammer-so-everything-looks-like-a-nail approach, using an easily measured metric that is indirect and variable, and the neglect of the particular for the useless general. This is clearly a situation where testosterone/estrogen levels are only one relatively minor variable, and the more interesting factors would be allelic variations, genetic background, and social/cultural effects. But hey, we can measure fingers with calipers, easy, and then we can through questionnaires or easy, fast, noninvasive tests at a handy population, and look! Numbers! Must be science, then.

Except that we don't really learn very much from it, other than that I'm really beautiful, despite what I actually look like.

Ferdenzi C,
Lemaître J-F,
Leongómez JD,
Craig Roberts SC (2011)
Digit ratio (2D:4D) predicts facial, but not voice or body odour, attractiveness in men.
Published online before print April 20, 2011, doi: 10.1098/rspb.2011.0544 Proc. R. Soc. B

Manning JT, Barley L, Walton J, Lewis-Jones DI, Trivers RL, Singh D, Thornhill R, Rohde P, Bereczkei T, Henzi P, Soler M, Szwed A. (2000) The 2nd:4th digit ratio, sexual dimorphism, population differences, and reproductive success. evidence for sexually antagonistic genes? Evol Hum Behav. 21(3):163-183.