Courtesy John DownerHave 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.