Claims by two researchers that they have isolated DNA from a 1.8 million-year-old hominid have been dismissed by leading palaeoarchaeologists.
Tom Loy of the University of Queensland, Australia, and Bonnie Williamson of Witwatersrand University, South Africa, are reported to have found a minute sample of blood on an ancient stone tool from South Africa鈥檚 famous Sterkfontein valley. They isolated DNA from that sample and sequenced it.
鈥淭he DNA we have found is something between a chimpanzee and a human, which suggests a hominid,鈥� Williamson told Johannesburg鈥檚 Mail & Guardian newspaper.
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However, Alan Cooper of the Ancient Biomolecules Centre in Oxford, UK, says it is much more likely to be blood from a modern-day archaeologist.
鈥淭his is yet another ancient DNA claim that is totally lacking in experimental and intellectual rigour,鈥� Cooper told New Scientist. 鈥淓verything we know about ancient DNA tells us that it can鈥檛 be correct.鈥�
Chris Stringer, a palaeontologist at the Natural History Museum in London, agrees: 鈥淚 do not believe that DNA of that age could be that well preserved.鈥�
Deep freeze
The oldest sample of DNA successfully isolated to date was about 50,000 years old, and came from a deep frozen mammoth. Most researchers think the theoretical limit for extraction is about 100,000 years old. After this time, DNA becomes too degraded to study.
Cooper says the results of the DNA sequencing of the blood sample could have a simple explanation. 鈥淚f it鈥檚 human DNA left by some archaeologist and it鈥檚 been there for 10 or 15 years, inevitably you would get damage to DNA sites from oxidation, UV light, and so on. So the sequence that you get back wouldn鈥檛 be quite human.鈥�
Previous claims by other researchers that they have obtained such ancient DNA have all been proved false. Loy and Williamson were uncontactable on Tuesday, but have said they plan more research to verify their study.