Research On Sex Lives of Ancestors Hints At Why Monogamous Humans Out-Competed Neanderthals

A research team from the University of Liverpool, led by Evolutionary Anthropology PhD student Emma Nelson, reckon theyve made some tenuous inroads into establishing just how much early human-like primates liked to play the field when it came to sex. With it, they may have found some clues as to why Homo sapiens managed to see off Neanderthals as the dominant species on the planet.

The secret is in the ratio between the index and ring fingers on human hands, which are thought to be telltale indicators of how much androgen and with it, testosterone a person is exposed to in the womb. More androgen means longer ring fingers and a lower index-to-ring finger ratio, and vice-versa; studies (highly contentious ones) have suggested that men and in some cases women exposed to a larger amount of androgen will probably be physically and sexually more competitive, whereas those with shorter ring fingers are more likely to be monogamous.

Nelson and co hunted down male primate fossils that contained hands with intact index and ring fingers two Neanderthals and one Australopithecus afarensis (an extinct hominid ancestor of modern humans) and got their measuring tapes out. The Neanderthal had longer ring digits, suggesting he was a promiscuous chap who spent more time chasing skirt than feathering the nest; the Australopithecus afarensis had shorter ring fingers, suggesting he was a faithful chap who cared for his mate.

They were, in technical terms, a non-pair bonded and pair-bonded male respectively. What theyre seeing is very interesting, commented Dean Snow of Pennsylvania State University, speaking to Discovery News, on Nelson and her teams findings. The difference between being pair-bonded and non pair-bonded mating is a major watershed within primates. If a distinction is that Neanderthals werent pair-bonded and modern humans were, that would be a major consideration in trying to figure out why modern humans out-competed Neanderthals in Europe.

The Neanderthal had longer digits, suggesting he was a promiscuous chap who spent more time chasing skirt than feathering the nest.

The difference would have been most crucial, Snow pointed out, when it came to pregnancy. A pair-bonded male would stick around to help his partner out with food and protection while she was in such a vulnerable condition, greatly improving her and her childs chances of survival. This monogamy would be beneficial to the future of the species too.

Its of course a massive leap from a set of stubby digits to solving one of the great conundrums of human evolution, and Nelson acknowledges that there is much more work to be done. Many more fossil hominids in particular skeletons of Homo sapiens that lived at the same time as Neanderthals need looked at. But it seems there is much to be learned from the sex lives of our ancestors, and as much to be learned from the backs of our own hands.

Picture by Dan Shouse. Some rights reserved.