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. "It has, for instance, slightly heavier eyebrows than the average person, and is generally somewhat more robust than average," she adds, explaining that modern humans have gradually evolved to become more slight and slender than upper Palaeolithic people were.
     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. 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. "Cioclovina did not meet any of these criteria - a strong refutation of the hypothesis that it represents a hybrid," Harvati says.
     The researchers, however, do not rule out that interbreeding may have taken place. "Modern humans and Neanderthals are very closely related species, so it is possible that, like living closely related species of primates today, they could have interbred to a limited degree," she says. "[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. Professor Eric Delson, chair of the Department of Anthropology at Lehman College, City University New York, also supports the conclusions, adding 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".

Sources: ABC, Discovery News (10 December 2007)