Saturday, September 20, 2008

More about finger length

Let's take a closer look at that last post. The person who wrote the UPI piece didn't interpret the original paper the same way I did. The finger measurement they were using was the ratio between the length of the index finger (2D) and the ring finger (4D).

Since as early as the 19th century(1), people have noticed that men tend to have a lower 2D:4D ratio than women. Since then the ratio has been linked to a variety of sexual, psychological, and behavioral traits. The number tends to be lower for men, for people with greater athletic prowess, assertive women, engineers, mathematicians, and lesbians. So they call a lower number a "masculinized" 2D:4D ratio.

But it's different in mice. Mice with a HIGHER ratio are more aggressive, more likely to bite when handled, and have a higher daily level of activity.

In the study cited here, the investigators selectively bred mice to be more active; they selected the mice that liked to run in their wheels more and bred them to each other. Then they measured their fingers. Voila. They had a HIGHER 2D:4D ratio.

So does this mean that finger length has any biological implication for behavior, physical prowess, or sexuality? Here's what the authors said:

"Given the many factors that have the ability to affect digit ratio, it is clearly more complicated than a simple testosterone-driven manliness metric."

I couldn't have said it better. Yeah, there might be some hormonal thing going on, but as it stands, it's no more scientific than trying to guess what's going on in a person's head by mapping the bumps on the skull.

(1) Anthropological Notes on the Human Hand Frank Baker
American Anthropologist Jan 1888, Vol. 1, No. 1: 51–76.