Yesterday's big news was the announcement from Leicester University researchers saying they successfully identified the bones of King Richard III — a conclusion they proclaimed was "beyond a reasonable doubt." Less than a day later, a swarm of people are now crying foul, saying that the paper has yet to be peer reviewed, and that the methodology used may not stand the scrutiny from DNA experts.
Indeed, the critical contention is the claim being made by the Leicester researchers that they successfully matched Richard's DNA to a living ancestor, the Canadian Michael Ibsen. It's an open-and-shut case, they say. But some experts have a bone to pick with the researchers.
Stephanie Pappas writes in LiveScience:
"The DNA results presented today are too weak, as they stand, to support the claim that DNA is actually from Richard III," said Maria Avila, a computational biologist at the Center for GeoGenetics at the Natural History Museum of Denmark. "Perhaps more in-depth DNA analysis summed to the archaeological and osteological [bone analysis] results would make a round story."
As Pappas notes, ancient DNA is very susceptible to contamination. She continues quoting Avila:
"Before being convinced of ANY aDNA study, it should be explicit that all possible cautions were taken to avoid potential contamination," Avila wrote in an email to LiveScience. "It is just part of the protocol." (aDNA refers to ancient DNA.)
Avila also warned that people could share mitochondrial DNA even if they didn't share a family tree. To be confident that Ibsen is related to the owner of the disinterred skeleton, the researchers must present statistics showing how common the DNA profile is in the United Kingdom, she said. Otherwise, the similarities between Ibsen's mitochondrial DNA and the skeleton's could be coincidental.
Of course, what Pappas meant to say was how common the DNA profile is in the United Kingdom and Canada (where Ibsen lives).
New Scientist's Douglas Heaven reports on similar concerns:
Mitochondrial DNA is passed down the maternal line and has 16,000 base pairs in total. Typically, you might expect to get 50 to 150 fragments from a 500-year-old skeleton, says Ian Barnes at Royal Holloway, University of London, who was not involved in the research. "You'd want to get sequences from lots of those fragments," he says. "There's a possibility of mitochondrial mutations arising in the line from Richard III."
"It's intriguing to be sure," says Mark Thomas at University College London. It is right that they used mitochondrial DNA based on the maternal line, he says, since genealogical evidence for the paternal lineage cannot be trusted.
But mitochondrial DNA is not especially good for pinpointing identity. "I could have the same mitochondrial DNA as Richard III and not be related to him," says Thomas.
The researchers used the two living descendents to "triangulate" the DNA results. The evidence will rest on whether Ibsen and his cousin have sufficiently rare mtDNA to make it unlikely that they both match the dead king by chance.
They must also not be too closely related. If Richard III's living descendants shared a common female ancestor even 150 years ago, their DNA could still be too close for the pair to count as distinct samples, says Thomas.
The Guardian's Alok Jha also chimes in:
Ross Barnett of the Centre for GeoGenetics at the Natural History Museum in Copenhagen also questioned the depth of the mtDNA match between the skeleton and Ibsen.
"The [diagrams] they showed were only about 30 base pairs or so … you need to have quite a lot more than 30 base pairs to get a deep match." The more common a mtDNA type is in the population, the more base pairs of DNA are required to get a reliable match.
These criticisms are all valid, no doubt, and it will be interesting to see how the paper fares in peer review. But it's also important to remember that other clues were used as well, including radiocarbon dating and historical accounts.
Images: University of Leicester.