JOIN USResearchers from Oxford, Liverpool, Southampton and Calgary universities reached their conclusion by measuring the fossilised finger bones of early extinct apes and extinct members of our own lineage — hominins.
The ratio of the second to the fourth finger can be used as an indicator of mating behaviour in primate species.
Previous studies by the research team have shown that promiscuous species have low index to ring finger ratios while monogamous species have high finger ratios. High levels of androgens, such as testosterone, increase the length of the fourth finger in comparison to the second finger.
It is thought that prenatal androgens affect finger length during development in the womb, which in turn is linked to competitiveness and promiscuity.
In this latest study, the finger ratios of early apes were low suggesting they were highly promiscuous, similar to the living great apes. However, hominins were found to be split:
Ardipithecus ramidus (around 4.4 million years old) appeared to be highly promiscuous, while Australopithecus afarensis (around 3-4 million years ago) was more likely to be monogamous.
However, Neanderthal ratios and those of an early human from Israel (dated to 90,000 years old) suggest that both groups may have been more promiscuous than most living human populations.