DNA Extracted From Blood of 1.8-Million-Year-Old Hominid
July 26 2001
If the find at a local World Heritage Site is authenticated, it could be the oldest such sample yet extracted.
Two researchers claim that they have extracted the DNA of a 1,8-million-year-old hominid from microscopic traces of blood found on stone tools excavated at the Sterkfontein Caves.
It is a discovery, scientists say, that could revolutionise the study of ancient DNA and the origins of mankind.
"The DNA we have found is something between a chimpanzee and a human, which suggests a hominid," explains Wits University micro archaeologist Bonnie Williamson.
Williamson and Professor Tom Loy of the University of Queensland believe that this DNA sequence is that of either our direct ancestor Homo habilis or Paranthropus robustus. If their findings are verified it would be the oldest DNA yet extracted.
The oldest DNA so far sequenced and independently verified is from a 50 000-year-old woolly mammoth.
"We strongly suspect that the DNA that we have is that of a hominid, but we still want to conduct more research to verify our claim," says Loy, who plans to publish the findings in a leading scientific journal soon.
The DNA they have sequenced is one base point of that of human DNA. In comparison, the DNA of a chimpanzee, human's closest relative, is three base points away from that of a human's.
What Loy feels gives credibility to the research is that both he and Williamson, his PhD student, got the same results using different techniques and working in laboratories on different continents.
Loy had discovered the minute quantities of blood on the Sterkfontein stone tools several years ago while examining them under an electron microscope. "Blood is a remarkably tough residue that can survive for long periods of time. Even artefacts that have been washed in laboratories often still have traces of blood on them," he says.
To extract the DNA from the blood sample Loy used a technique called polymerase chain reaction to replicate the short strands of DNA. Care had to be taken to avoid modern DNA contamination of the sample.
Some scientists have expressed caution over Loy and Williamson's claim. There have been false alarms in the study of ancient DNA. In 1995 a scientist announced that he had extracted DNA from an 80-million-year-old dinosaur bone. Other researchers concluded that the dinosaur DNA was that of a mammal.
Even a sneeze or a speck of dust containing human skin or hair can contaminate a sample.
"We took all the necessary precautions, we used bleach to sterilise surfaces and ultraviolet light to destroy any other modern DNA," says Loy, who in the past 12 years of ancient DNA research has had only one contamination.
"Obtaining DNA that is older than 100 000 years some academics believe is chemically impossible as the DNA has decayed to such an extent.
So far no one has been able to independently authenticate DNA of that age or older. It usually turns out to be a contamination," says Dr Paulette Bloomer of the department of genetics at the University of Pretoria.
Bloomer was unsuccessful in attempting to extract DNA from a blind sample of primate teeth that she suspected was older than 100 000 years.
But both Bloomer and Professor Terry Robinson of the department of zoology at the University of Stellenbosch believe if the findings are independently verified in another laboratory then the hominid DNA will be the oldest yet extracted and it will be a major breakthrough for science.
"We still want to do more work on the DNA. For one we want to see if we can extract hominid DNA from fossilised teeth ," Loy says.
Not only suspected hominid blood was identified on the stone tools -- other residues were also found.
Williamson believes she has extracted the DNA from another blood sample, which she has identified as belonging to the bovid family.
"Also found on the artefacts were samples of bone that suggests these stone tools were used to make and sharpen bone tools.
"We have also identified starch grains from several plant species, including a tuber from the hypoxis family. There is also residue from a number of wooded plants," says Loy.
Loy believes the hypoxis tuber was dug up and eaten.
"What we are in the process of doing is building up a database of DNA references so that we can identify some of these residues.
"There are plans to collect DNA samples from animals in the San Diego zoo. In November I plan to return to South Africa to do a bit of plant hunting out in the bush."
If the DNA on the Sterkfontein tools is in fact that of a hominid, palaeontologists will have to do a little detective work to explain how the blood got on to the artefacts.
"Anyone who has tried to make a replica of one of these tools soon realises that it is inevitable that you will nick yourself and bleed. I think that is what happened with these hominids," Loy speculates.
The site where the tools were found is included in the Sterkfontein valley area that was declared a World Heritage Site by Unesco in 1999.
The Sterkfontein valley is particularly rich in fossils because of its geological conditions. The dolomite caves are slightly alkaline, which preserves bones by encouraging calcification.
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