Did modern humans interbreed with Neanderthals and, if so, did the mating result in a half-human, half-Neanderthal hybrid?
The answer is possibly ‘yes’ to the interbreeding but ‘no’ to the hybrid, according to the authors of a new study that is already making waves among anthropologists.
At the centre of the study, published online in the Journal of Human Evolution, and the current debate, is a 29,000 year old Romanian skull that is one of the oldest fossils in Europe with modern human features.
But those features aren’t quite a perfect match with us, which has led some experts to suspect it was a cross between a Neanderthal and a modern human.
That’s not so, according to study leader Dr Katerina Harvati, a senior researcher in the Department of Human Evolution at the Max Planck Institute for Evolutionary Anthropology and adjunct associate professor of anthropology at the City University of New York Graduate School.
“It differs from living people only in subtle ways, and always well within the range of modern human variation,” says Harvati, who worked with the Max Planck Institute researcher Dr Philipp Gunz and Professor Dan Grigorescu, from the University of Bucharest.
She and her team took detailed 3D measurements of the Romanian skull, called Cioclovina calvaria, and compared these with a similar head shape analysis of Neanderthals, modern humans and fossils of other hominids found in Europe, Africa and countries bordering the eastern Mediterranean Sea.
The researchers also studied animal hybrids and developed an unprecedented list of proposed criteria for evaluating whether or not a fossil specimen is a hybrid.
The criteria include: greater or much smaller size than the parental species, on average; evidence for developmental instability; possible occurrence of rare attributes, such as having extra teeth or bone joints; and possessing an intermediate shape.
“Cioclovina did not meet any of these criteria—a strong refutation of the hypothesis that it represents a hybrid,” Harvati says.
The scientists support the ‘single origin’ model of human evolution.
This holds that modern humans evolved between 200,000 and 100,000 years ago in a single location, mostly likely Africa, with subsequent migration displacing archaic hominid populations, including Neanderthals, around the world.
The researchers, however, do not rule out that interbreeding may have taken place.
“[If it occurred] it was probably a rare event and the result was not significant in evolutionary terms.”
Dr Ian Tattersall, curator in the Division of Anthropology of the American Museum of Natural History in New York says he is “thoroughly in agreement” with the new study.
“The strenuous search for a Neanderthal-modern human hybrid has yet to turn up any evidence of such a thing.”
Delson [Professor Eric Delson, chairman of the department of anthropology at Lehman College] adds that, when combined with recent genetic studies that have found “indications of low to nonexistent” levels of Neanderthal genetic imprinting on modern humans, the new findings lead “us to reject widespread hybridisation and thus a major influence of Neanderthals on later human populations in Europe”.