Have you fallen in love with a runner? Science may have discovered why. In a study published on Wednesday in the scientific journal PLoS One, researchers studied participants in the 2013 Robin Hood Half Marathon, charting their finishing times and comparing that to the length of their fingers.
According to previous studies, a lower second-finger-to-fourth-finger (2D:4D) ratio has been proven as a marker for higher sperm count in men, along with a higher level of testosterone. According to the new study, in which researchers polled 439 men, runners with a lower digit ratio performed better over the 13.1-mile distance.
“A marker of testosterone exposure is therefore associated with running ability,” the study concludes, “which ethnographic evidence has shown to be an important attribute for hunting.”
The “ethnographic evidence” the study refers to is primitive man’s use of distance running to hunt prey, commonly called persistence hunting. This hunting method can still be observed in disparate cultures such as the Tarahumara tribe of Northern Mexico and the Kalahari in Africa, according to the report.
“Since testosterone is widely associated with reproductive success, an association between testosterone and endurance running would make running prowess a reliable signal of male reproductive potential,” the study says. “It may be that women are attracted to men with the capacity to ‘get,’ rather than those who ‘have.’”
Researchers say the next step will be to test this conclusion against hunting societies.