Wednesday, December 22, 2010

2D-4D Studies: A Changing Simple Theory?

Remember the theory about comparing the length of the forefinger (2D) to the length of the ring finger (4D)? The idea is that a long ring finger compared to the forefinger is evidence of prenatal testosterone exposure, at least within the male sex. I earlier wrote about one study which found that male stockbrokers with especially low 2D/4D ratio (indicating a longer ring finger than forefinger) seemed to earn humongous amounts of money. This was explained by their greater willingness to take risks, based on that presumed prenatal testosterone bath.

When I wrote that earlier post, I got really annoyed by this:

"Men typically have a ratio below 1, indicating their ring fingers are longer, Coates said. Women typically have a ratio of 1 or above."

So Coates is arguing that the average woman has forefingers longer than her ring fingers? I tried to Google more about this topic and only came across something in Desmond Morris' (of all people!) book The Naked Woman:

Despite its importance the forefinger is usually only the third longest of the four fingers, being exceeded in most cases by the middle finger and the ring finger. In 45 percent of females, however, it is the second longest finger, relegating the ring-finger to third place. Surprisingly, this is true of 22 percent of males.
The reason for my irritation is that I had never noticed any women having equally long forefingers and ring fingers. It seems that this is something I should have noticed, you know, if the above assertion was to be taken as a universal one.

But all is made much clearer now. A recent study carried out with data from Finnish women gives the 2D-4D average figure for right hands as 0.978 and for left hands as 0.972. Compare these values with the above quote. No wonder that I didn't believe that assertive statement.

The 2D-4D ratio seems to show genetic differences between countries or at least differences as one moves northwards. This is a good example of a changing simple theory, perhaps even a dying one.

The reason for the latter speculation is that several recent studies fail to find support for the idea that the digit ratio can tell us much about, say, the fertility behavior of individuals. Indeed, my random surfing among these studies seemed to pick up mostly negative results. An example:

We failed to demonstrate meaningful relations between the radiographic 2D:4D index and the wide scale of studied variables. Despite the ideal set-up of the measuring possibilities in a relatively large radiographic material the variables currently studied were not dependent on the length of finger bones. It can therefore be questioned whether any real associations between the bony 2D:4D index in adult life and (direct or indirect) hormone dependent effects exist. There may be a publication bias explaining that mostly positive findings have been previously reported. This study cannot rule out the possibility that the previously found associations between the 2D:4D index and several items are due to finger soft tissues.

What's the point of this post? Not to criticize the digit ratio studies as such, but to point out that the popularizing media is nowhere to be found when things get less clear-cut or when negative results predominate. It's all hullabaloo with the initial findings (assuming they show youknowwhat) and after that, snores.