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The first ancient DNA sequences to be gathered - 3400 base pairs from a 2400-year-old Egyptian mummy - were a proof of principle. A full genome sequence would be far more informative - perhaps explaining what killed King Tut, for instance. At present, Inuk's is the only published ancient human genome. However, a team led by Svante Paabo and Ed Green at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Gennany, will soon publish the complete genome sequence combined together from several Neanderthals, from between 38,000 and 70,000 years ago.
Neanderthals are not the only hominids whose genomes could be sequenced, says Willerslev. Homo erectus, a species that emerged in Africa about 2 million years ago, survived in east Asia until less than 100,000 years ago. If well-preserved bones can be found, a genome might be possible, Willerslev says. Willerslev's laboratory has just received bones from Spain belonging to Homo heidelbergensis, the predecessor to Neanderthals. "We are basically starting on it right now," he says. If these genomes ever materialise - and that's a big if- they could lead to a better understanding of how different hominid species are related, and when and where they branched off. If the genetic infonnation is good enough, it may tell us something about the nature of past peoples - possibly even what they looked like. Ancient human genomes could give us insights into the evolution of our own species, explaining when genes involved in disease and higher cognitive skills emerged.
But DNA is not forever. As it ages, its long strands shred into ever smaller pieces. Eventually they become too small to reassemble, and all information is lost. "There seems to be a time horizon of 100,000 years or so under most preservation conditions during which intact DNA survives," Green says. Stephan Schuster at Pennsylvania State University, who led the woolly mammoth genome project, thinks ancient genomics is already plateauing. Large chunks of Inuk's genome couldn't be filled in because his DNA had crumbled into small pieces. "We will face an uphill battle in trying to apply this to a large number of human remains," he says.
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