(AFP) – Nov 2, 2010
PARIS — Neanderthals may be lampooned as slack-jawed low-brows who could just about wield a heavy club on a good day, but in one important respect they outperformed us: in the number of sex partners.
So says an unusual study which suggests finger length can indicate promiscuity among hominins, as the ancient family of humans is known.
Researchers led by Emma Nelson of Liverpool University, northwestern England, looked at fossilised fingers from four hominin species.
They comprised Ardipithecus ramidus, a hominid who lived around 4.4 million years ago; Australopithecus afarensis around three to four million years ago; Neanderthals, who disappeared around 28,000 years ago; and a fossil of an early Homo sapiens, as anatomically modern humans are known, from around 90,000 years ago.
Nelson's theory is based on the ratio between the length of the index finger as compared to the ring finger.
Previous research by her group concluded that exposure in the womb to key sex hormones known as androgens, which includes testosterone, affects finger length -- and future behaviour.
High levels of in-utero androgens increase the length of the fourth finger in relation to the second finger, which thus lowers the ratio.
They are also linked with competitiveness and promiscuity, according to this work.
So how did the primates line up?
A low finger ratio showed Ardipithecus ramidus was likely to be randy, while a high finger ratio indicated Australopithecus afarensis was likely to be exclusive.
Meanwhile, low ratios from the Neanderthal and the early human "suggest that both groups may have been more promiscuous than most living human populations," say the authors.
The scientists admit that their approach is novel, and further evidence is needed to shed light on the social behaviour of ancient humans.
"Although finger ratios provide some really exciting suggestions about hominin behaviour, we do accept that the evidence is limited and to confirm these findings we really need more fossils," said Nelson.
The study's conclusions add a new element of debate over human lineage. More promiscuous species of hominins would have an advantage over monogamous ones, in terms of numbers and the size of the gene pool.
"Pair-bonding, in a broad sense, is universal among humans, but it is not known when the transition from a promiscuous mating system to a stable bonded one occurred," observes the paper, published by the British journal Proceedings of the Royal Society B.
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