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The study of modern human origins has traditionally relied on fossil and archaeological data, and genetic studies of living populations. But in recent years researchers have succeeded in retrieving ancient DNA from fossils, adding a compelling new data set to the mix. So far, scientists have focused on DNA from Neandertals, a population of archaic humans who inhabited Europe and western Asia. The sample size is small (DNA from three specimens has been analyzed), but the results indicate that Neandertal DNA¿at least the DNA from the cell's energy-producing organs, the mitochondria¿differed from our own. As a result, a number of researchers concluded that Neandertals must therefore have been a separate species. Critics, however, have charged that without mitochondrial DNA (mtDNA) data from anatomically modern humans of similar antiquity for comparison, such differences are virtually meaningless. Now new research published today in the Proceedings of the National Academy of Sciences is filling in that gap, and the results may force some scholars to reconsider the evolutionary position of the Neandertals.
Gregory J. Adcock of the Australian National University and his colleagues retrieved and studied mtDNA from the fossilized remains of 10 ancient but anatomically modern Australians, including a 60,000-year-old specimen known as Lake Mungo 3 (LM3). Intriguingly, like the Neandertal mtDNA studies, analysis of the LM3 sequence revealed an mtDNA lineage that no longer exists as such in living humans. "If the mtDNA present in a modern human (LM3) can become extinct, then perhaps something similar happened to the mtDNA of Neandertals," population geneticist John H. Relethford of the State University of New York at Oneonta writes in a commentary accompanying the PNAS report. "If so, then the absence of Neandertal mtDNA in living humans does not reject the possibility of some genetic continuity with modern humans." That is, the much maligned Neandertals may well be among our ancestors.
