We Are All Africans
Neandertals as European Ancestors?
The genetic evidence to which he refers has accumulated over the last six years, but the most dramatic advance came in 1999, when a team led by Svante P??bo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, became the first to extract mtDNA from the original Neandertal specimen. His group's success was a spectacular tour de force of meticulous technique and solid research design. The ancient mtDNA was compared with mtDNA from more than 2,000 people living in various regions around the world and differed from each of the modern regional groups by an average of 27 mutations (out of a possible 379 that were examined). Contrary to the predictions of the Multiregional hypothesis, the mtDNA of Neandertals was not closer to that of the modern Europeans. The work was a strong blow to the theory that humans evolved in several places simultaneously.
Multiregionalists Milford Wolpoff of the University of Michigan and Alan Thorne, then of Australian National University in Canberra, challenged the conclusions. They urged an investigation of mtDNA from additional Neandertals, in case the single individual used by Paabo's team was particularly unusual. They also suggested that Neandertal mtDNA might be closer to samples from the fossilized remains of early modern humans in Europe than from living Europeans.
Since these criticisms were levied, several teams have carried out additional studies of mtDNA from Neandertals and fossilized modern humans. All have shown that Neandertal samples differ significantly from modern
mtDNA, which is indistinguishable from fossilized modern human mtDNA. Giorgio Bertorelle of the University of Ferrara in Italy led one of these teams, which published important results last May. Bertorelle's team compared mtDNA from two early modern humans (Cro-Magnons) from Italy, dated to 23,000 and 24,720 years old, with four mtDNA sequences of Neandertals from 42,000 to 29,000 years ago. The chronological proximity of the Neandertal and modern fossils was key because it increased the likelihood that Neandertal mtDNA would strongly resemble the early modern human mtDNA—if the former evolved into the latter, as the Multiregional hypothesis states.
Bertorelle and colleagues found that the Cro-Magnon mtDNA was unlike the Neandertal samples, differing from them at 22 and 28 sites out of 360. Instead, the Cro-Magnon mtDNA sequences fell squarely within the range of variation of living humans. One of the Italian Cro-Magnons had a sequence shared by 359 (14 percent) of 2,566 modern samples in Europe and the Near East, and the other differs by only one mutation.
"The early modern humans had sequences that living individuals still have," concluded Bertorelle, "they [have] ... nothing to do with Neandertal sequences." He and Asfaw might chime in unison that Neandertals cannot represent a regional European transition from Homo erectus to modern Homo sapiens.
The identity between Cro-Magnon and modern human mtDNA sequences in this study and others is striking, and it has caused some researchers to worry about the possibility of
mtDNA contamination from researchers or others who have handled the fossils. Although contamination is a major problem in such studies, Bertorelle asserts spiritedly that his data are clean, stating that his group performed nine different tests to check for contamination and followed the most stringent procedures and methodology. He also points out the irony of questioning the validity of the mtDNA of a prehistoric human only because it is identical to that of modern humans.
» Post Comment