Researcher Emma Nelson of Liverpool University has conducted an interesting study regarding finger length and promiscuity, based on studying fossilized hands of four hominin species.
The length of our fingers is controlled by the hormone levels we are exposed to in the womb and apparently the ratio of index finger to ring finger has been determined to be an indication of increased promiscuity in certain hominin species. "High levels of in-utero androgens increase the length of the fourth finger in relation to the second finger, resulting in a low ratio." Essentially a low ratio (little distance in length of these two fingers) is linked to being promiscuous and high ratio (larger distance in length) linked to being exclusive. In our evolutionary history, it seems based on finger length, both Neanderthals and early humans were more "promiscuous than most living human populations," say the authors.
Image Credit: Science/AAAS