Handsome By Chance: It Is Not About Makeup For Neanderthals
Chance, not natural selection, best explains why the modern human skull looks so different from that of its Neanderthal relative, according to a new study led by Tim Weaver, assistant professor of anthropology at UC Davis
Model of the Neanderthal man. Exhibited in the Dinosaur Park Münchehagen, Germany. (Credit: iStockphoto/Klaus Nilkens)
“For 150 years, scientists have tried to decipher why Neanderthal skulls are different from those of modern humans,” Weaver said. “Most accounts have emphasized natural selection and the possible adaptive value of either Neanderthal or modern human traits. We show that instead, random changes over the past 500,000 years or so – since Neanderthals and modern humans became isolated from each other – are the best explanation for these differences.”
Weaver and his colleagues compared cranial measurements of 2,524 modern human skulls and 20 Neanderthal specimens, then contrasted those results with genetic information from a separate sample of 1,056 modern humans.
The scientists concluded that Neanderthals did not develop their protruding mid-faces as an adaptation to icy Pleistocene weather or the demands of using teeth as tools, and the retracted faces of modern humans are not an adaptation for language, as some anthropologists have proposed.
Instead, random “genetic drift” is the likeliest reason for these skull differences.
Weaver conducted the research with Charles Roseman, an anthropologist at the University of Illinois at Urbana-Champaign, and Chris Stringer, a paleoanthropologist at the Natural History Museum in London.
Journal of Human Evolution Volume 53, Issue 2, August 2007, Pages 135-145 doi:10.1016/j.jhevol.2007.03.001
Were neandertal and modern human cranial differences produced by natural selection or genetic drift?
Timothy D. Weaver a, b, Charles C. Roseman c and Chris B. Stringer d
aDepartment of Anthropology, University of California, One Shields Avenue, Davis, CA 95616, USA
bDepartment of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, D-04103 Leipzig, Germany
cDepartment of Anthropology, University of Illinois at Urbana-Champaign, 109 Davenport Hall, 607 South Matthews Avenue, Urbana, IL 61801, USA
dDepartment of Palaeontology, The Natural History Museum, London SW7 5BD, UK
Received 10 July 2006; accepted 1 March 2007. Available online 23 May 2007.
Most evolutionary explanations for cranial differences between Neandertals and modern humans emphasize adaptation by natural selection. Features of the crania of Neandertals could be adaptations to the glacial climate of Pleistocene Europe or to the high mechanical strains produced by habitually using the front teeth as tools, while those of modern humans could be adaptations for articulate speech production. A few researchers have proposed non-adaptive explanations. These stress that isolation between Neandertal and modern human populations would have lead to cranial diversification by genetic drift (chance changes in the frequencies of alleles at genetic loci contributing to variation in cranial morphology). Here we use a variety of statistical tests founded on explicit predictions from quantitative- and population-genetic theory to show that genetic drift can explain cranial differences between Neandertals and modern humans. These tests are based on thirty-seven standard cranial measurements from a sample of 2524 modern humans from 30 populations and 20 Neandertal fossils. As a further test, we compare our results for modern human cranial measurements with those for a genetic dataset consisting of 377 microsatellites typed for a sample of 1056 modern humans from 52 populations. We conclude that rather than requiring special adaptive accounts, Neandertal and modern human crania may simply represent two outcomes from a vast space of random evolutionary possibilities.
Keywords: Neandertals; Hominin evolution; Evolutionary quantitative genetics; Population genetics