DNA of long-dead cows read from pages of Medieval books
Hidden messages - Courtesy of The Chapter of York
You could call it reading behind the lines. When medieval scribes sat down to preserve the literature and records of their day, they often wrote on parchment – a paper-like material made from animal skins. What they didn’t know was that the parchment holds DNA that can provide information about medieval life – and might even hold clues on how to preserve the ancient documents more effectively.
Seven years ago, Matthew Collins at the University of Copenhagen in Denmark and his colleagues had the idea of applying state-of-the-art genetic analysis techniques to the animal skin pages of medieval documents.
“We realised all these dead cows have a date written on them,” he says. “We thought, ‘This is crazy, why aren’t we exploiting this’.”
Collins and researchers from the University of York, UK, and Trinity College Dublin in Ireland turned to the York Gospels, among other texts, to see what the DNA could show. The York Gospels are thought to have been written around the year AD 1000.
In standard ancient DNA studies, geneticists physically extract material from old animal bones for analysis. But this approach is too invasive to apply to priceless manuscripts.
Instead, the team turned to conservators for help. They periodically clean books like the York Gospels with rubber erasers. The waste rubbings are usually thrown away, but Collins and his colleagues carefully collected and analysed them to see what proteins and DNA were present.
The proteins helped identify the animals used to make the book’s pages – mostly cattle in the case of the York Gospels, with some pages made from sheepskin. The DNA also revealed the sex of the animals that provided some of the parchments – most were female. Knowing information like this could, in future, help the researchers understand which livestock populations contributed to parchment making. Or it might even show how bookmakers periodically changed their materials following an outbreak of disease among specific kinds of livestock.
Perhaps more useful, as far as conservators are concerned, is the detection of DNA from bacteria including Saccharopolyspora. This genus is associated with unsightly spots that can develop on old parchment manuscripts. Finding it could alert conservators to the likelihood of the spots appearing on the manuscripts.
Just knowing the type of animal used is useful, says book and paper conservator Emma Nichols at Cambridge University Library. This is because, in their work, conservators often try to match replacement materials with those originally used so that the conservation work is as sympathetic to the document as possible.
The DNA reveals other secrets too. For instance, pages containing oaths for clergy that would have been touched and kissed regularly were associated with higher levels of human DNA.
“You can even see the use to which the text is being put, which is kind of amazing,” says Collins.
“We are all accustomed to hearing research termed ‘ground-breaking’ – that is not in any way an overstatement here,” says Timothy Stinson, an English professor at North Carolina State University. He points out that a year-by-year record of domestic animals spanning more than a millennium has essentially been preserved in European libraries.
“It is the type of collaboration between arts and humanities and science which one wishes to see more often,” says M. A. Michael at the University of Glasgow, UK.
Michael says that some of the findings – such as discovering which pages in a book of gospels were used most frequently – would already have been known to scholars. But he believes the possibility for mapping animal distribution in the period using such analysis is new.
The team has also applied the same techniques to another text, the Gospel of Luke owned by Corpus Christi College, Cambridge, which dates from the 12th century. They found that the book is a veritable menagerie – made with skins from calves, sheep, goat and two species of deer.
Journal reference: Biorxiv, DOI: 10.1101/146324