Fossilized Fingers Reveal Ancestors' Behavior

A joint research between scientists and researchers from the universities of Liverpool, Southampton and Calgary, found out more about the social behavior of ancient hominins by analyzing their fossilized fingers.

They used fossilized skeletal remains of ancient apes and extinct hominins, and determined the levels of exposure to prenatal androgens, experienced by these species.

Prenatal androgens are a group of hormones very important for the development of masculine characteristics like aggression and promiscuity, and it is believed that androgens like testosterone, affect finger length during development in the womb.

High hormone levels make the fourth finger longer than the second one, which gives a low index to ring finger ratio.

“It is believed that prenatal androgens affect the genes responsible for the development of fingers, toes and the reproductive system,” explains Emma Nelson, from the University of Liverpool's School of Archeology, Classics and Egyptology.

“We have recently shown that promiscuous primate species have low index to ring finger ratios, while monogamous species have high ratios.

“We used this information to estimate the social behavior of extinct apes and hominins, [and] although the fossil record is limited for this period, and more fossils are needed to confirm our findings, this method could prove to be an exciting new way of understanding how our social behavior has evolved.”

Dr Susanne Shultz, from the Institute of Cognitive and Evolutionary Anthropology at the University of Oxford agreed and said that “social behaviors are notoriously difficult to identify in the fossil record,” this is why “developing novel approaches, such as finger ratios, can help inform the current debate surrounding the social systems of the earliest human ancestors.”

The analysis carried out by the researchers included the fossil finger bone ratios of Neanderthals and early apes, as well as hominins, Ardipithecus ramidus and Australopithecus afarensis, to further understanding of their social behavior.

The results showed that the fossil finger ratios of Neanderthals and early hominins were lower than for most living humans, so this can only mean that they had been exposed to high levels of prenatal androgens.

In other words, early humans were more competitive and promiscuous than people are today.

Another conclusion drawn from the research is that the early hominin, Australopithecus – dating from nearly 3-4 million years ago, was most probably monogamous, while the earlier Ardipithecus seems to have been very promiscuous and more similar to living great apes.

In order to fully understand the social behavior of these two groups, further fossil studies are necessary.

This research was supported by the British Academy Centenary Research Project, Lucy to Language and published in Proceedings of the Royal Society B.