Mummy DNA: History or hype?


Last February, you got a glimpse of the first DNA study of Egyptian mummies—research that suggested King Tut was the product of brother/sister incest, among other discoveries. But recently, complaints from geneticists have started surfacing, making the earlier study—which was largely overseen by Egyptologists and mummy experts, including newly appointed Egyptian Minister of Antiquities, Zahi Hawass—seem seriously flawed.

At the heart of this story is a dispute over methodology. What is the right way to assess the DNA of a mummy? And, beyond that, is the DNA of a mummy likely be intact enough to tell you anything at all? Hawass' team diverged from majority opinion on both counts. And, because they haven't published their raw data, the concerned geneticists haven't been able to judge for themselves whether the unorthodox methods were valid. Jo Marchant wrote an article on the geneticists' critiques for New Scientist, and she delves deeper into the story on her own blog:

Critics are especially concerned by the method that Hawass's team used to analyse the mummy DNA. The DNA in ancient samples is generally degraded, present in very small amounts, and contaminated with modern DNA. This is a particular problem for human samples, where you have to work out whether the DNA you have belongs to the original individual or to other people who have come into contact with the body in modern times.

Ancient DNA researchers usually start by trying to amplify and sequence mitochondrial DNA (mtDNA). There are thousands of copies of this in every cell, so it is much easier to work with than genomic DNA, of which there are only two copies in every cell.

But the JAMA paper doesn't mention mtDNA. Instead, the researchers used genetic fingerprinting to construct their family tree. You might think that genetic fingerprinting, famous for its use in criminal investigations, should give black-and-white results. But it can actually be very subjective, particularly for poor quality samples (for example see Linda Geddes' excellent investigation).

Genetic fingerprinting involves testing variable regions of the genome called microsatellites. These are made up of short sequence repeats, the exact number of which differs between individuals and is inherited from parent to child. Each microsatellite region is amplified using a technique called polymerase chain reaction (PCR), then researchers estimate from the size of the product how many repeats it must contain. By comparing individuals over a number of such regions, it's possible to work out whether or not they are related. The problem is that PCR amplifies modern contamination as well as ancient DNA, and simply checking the size of the products offers no way to distinguish between the two.

With the current political situation in Egypt—where all the mummy DNA research was done—it'll probably be a while before there's any resolution on this issue. Zahi Hawass probably has bigger things on this mind right now.

But I think this is an interesting story, and one that's worth paying attention to—especially given the way Hawass' conclusions have already become accepted cocktail-party fact. That study was partially funded by the Discovery Channel, and its results were broadcast in a TV special. So, what happens if those results were wrong? This is shaping up to be a great example of the conflict between how the timeline and process of science works, compared to the timeline and process of journalism. Or, for that matter, edutainment.

Image: Flickr user jparise, via CC