Finger length as indicator of behavior

Curious langur
Curious langurCourtesy John Downer
Have you ever wondered why people honk at you .02 seconds after the light turns green? Or why some people take Connect Four a little too seriously? Well, it may be the length of their fingers. That’s right, the difference in length between your 2nd finger (or pointer finger) and your 4th finger (or ring finger) is thought to be an indirect measurement of testosterone levels you were exposed to during fetal development. The more testosterone, the longer your ring finger compared to you pointer finger.

In a recent study, researchers from the University of Liverpool and Oxford used this measurement to link aggressiveness in primates with the levels of prenatal testosterone in utero. They found that Old World monkeys tended to have a low 4th digit (4D) to 2nd digit (2D) ratio (i.e. their ring fingers were longer than their pointer fingers) and also exhibited aggressive, competitive, and promiscuous behavior. New World monkeys (like gibbons), on the other hand, along with Great Apes (like chimps and orangutans) tended to have a higher 2D:4D ratio. These species were found to exhibit much more cooperative and tolerant behavior. The results of the study have implications for our own social behaviors. We live in large multi-male, multi-female groups and are (usually) quite cooperative. This study, and more like it, could start to shed light on the origins of our sociality.

The use of digit ratio as a measurement of prenatal testosterone is not new, however. Many researchers have used it even in humans (we are primates after all) to try and predict various behaviors, aptitudes, and personal characteristics. For example, some of the traits suggested to correlate with low digit ratios (ring longer than pointer) include greater male fertility, assertiveness in women, and greater musical and athletic ability. These studies looked at the increased competitive nature brought out in individuals with exposure to high levels of prenatal testosterone.

So the next time someone cuts you off, just know it might be the case that their 4th digit is longer than their 2nd… so try to leave your 3rd digit out of it.

Your Comments, Thoughts, Questions, Ideas

JGordon's picture
JGordon says:

Cool article! I posted earlier this year about finger length and associated individual characteristics, but I had never heard about it being applied to general species characteristics. Interesting that it goes beyond (perhaps) trivial individual variation to the point where prenatal testosterone levels may have affected our development as a species.

posted on Wed, 11/11/2009 - 9:34am
Anonymous's picture
Anonymous says:

JGordon just wants to show off the photo of his highly masculinised finger ratio again!

posted on Wed, 11/11/2009 - 2:32pm
JGordon's picture
JGordon says:

That's a big part of it.

Plus, I want more people to accept my current excuse for being caught shoplifting last weekend.

posted on Wed, 11/11/2009 - 4:04pm
Liza's picture
Liza says:

I don't know what the delta between the two finger measurements has to be to be considered significant, but I'm feeling inadequate. Upon cursory inspection, my ring finger is probs only a few millimeters longer than my pointer finger. How do I excuse my cruddy behavior now?

Minimal difference: Alas.
Minimal difference: Alas.Courtesy Liza Pryor

posted on Thu, 11/12/2009 - 5:19pm
Anonymous's picture
Anonymous says:

You are walking on a slippery slope when suggesting certain physical charactersitics influence or are tied to other physical characteristics and definately so when you suggest it ties to ones behavior. There is a long history people doing this and in all cases the science is flawed. Things like saying one can tie skin color to intelligence for example. No you cannot. Physical traits are independent of each other tied to different gene loci-common to all people ( a species ).

posted on Thu, 11/12/2009 - 5:20pm
JGordon's picture
JGordon says:

You raise a good point, but I don't think anyone here is going quite that far.

While the study referenced above makes generalizations about various species of apes and monkeys, they are, after all, different species. When it comes to humans, as you say, we're all the same species, and so variation in things like finger length/prenatal testosterone exposure are going to come down to person-to-person differences. It's small behavioral associations in individuals, not differences between groups of people. And I think we're on fairly safe ground with something like testosterone—it's been pretty well established that levels of a hormone like testosterone (a physical trait) can affect behavior to some extent*. But, again, the affect it has varies from person to person, and even within a single person, because hormone levels can change over the course of your life.

*Obviously we all control our own behavior, but the way your brain and body feel and function will probably influence how you act, right?

posted on Thu, 11/12/2009 - 5:51pm

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