Tim Stinson carefully cuts a piece from one of the medieval parchment leaves used in the study. Genetic tests confirmed the parchment was made from calf skin.
Credit: C. Michael Stinson
Cutting a piece out of a page of a 15th-century prayer book may seem like sacrilege, but to one researcher, it's a small sacrifice in the name of solving medieval mysteries.
The goal is to build a DNA database of parchment to trace the lineage of ancient books.
Tim Stinson, an assistant professor of English at North Carolina State University, studies medieval texts and literature and how they changed through the Middle Ages. Though thousands of such texts have survived the centuries, the time and place of origin of many is unknown, which makes it hard to place manuscripts in their proper historical context.
Stinson and other researchers try to use clues from the texts themselves, such as handwriting and dialect, to divine a manuscript's origin, but "both of those things are tricky," Stinson said, because they are fairly inexact.
It was while poring over some texts and trying to puzzle out their origin that Stinson thought of a better method in what he calls his "aha moment" — instead of looking for the key in the words on the page, why not look at the code embedded in the pages themselves?
Most medieval manuscripts are written on parchment made from animal skin, which contains DNA. Stinson reasoned that if DNA, which contains all our genetic information, could be extracted from ancient bones and other sources, why not from these ancient hides?
"It just suddenly occurred to me," Stinson told LiveScience.
Stinson's plan, which he recently presented at the annual meeting of the Bibliographical Society of America in New York, is to take DNA samples from manuscripts with known dates and establish a reference base to which samples of texts of unknown origin can be compared. He hopes to do this by pinning down the specific herds of animals each piece of parchment came from and comparing pieces for potential family relationships.
If it works, it could make tracing the lineage of ancient books much easier.
So for the Middle Ages (roughly A.D. 450 to A.D. 1450), "a majority of what we have is going to be parchment, and parchment was still widely used even after paper was widely available" in more expensive books, Stinson said.
Surviving manuscripts can include: legal documents, such as deeds and leases; Church documents, including Bibles and choir and Mass books; devotional books for lay people; and from later in the time period, literary manuscripts.
While legal documents and writings from the Catholic Church, especially chronicles penned by monks, were usually dated, literary manuscripts almost never had a date attached.
For texts where the date and place of origin are uncertain, one can look at the style of handwriting, which changes with time (just as print faces do), as well as what dialects are used, which can be from very specific locations.
But both of these methods only give researchers a ballpark estimate on the source of a manuscript, "and what I'm trying to do is zero in a lot better than that," Stinson said.
The use of DNA in dating the manuscripts is helped along by the fact that there was little variation in the types of animals used for parchment in Europe.
"In Europe, it tended to be three types of animals used all the time, and that's calf, sheep and goat," Stinson said, adding: "And that varies geographically." So sheep were the animal of choice for parchment in England, while a mix of sheep and calves would have been used in France.
These animals were used because they were larger, and so yielded more skin, and because they were domesticated, "which means you have lots of them on hand," Stinson said.
Only young animals were used to make parchment because "once they become adults, the hide is just too thick to use for parchment anymore," Stinson said. The upper age limit for calves was about 11 months, he said.
Combining historical details, such as associations among regions and animals, with DNA data can help determine the origin of each piece of parchment in a book and establish similarities among the parchment in different books.
The first step to creating a DNA database of parchment was to see if DNA could even be extracted from the well-aged pages.
So Stinson bought six leaves of parchment that looked like they all once belonged in a 15th-century French prayer book. The leaves had wide enough margins that a square plug could be cut out without damaging any of the writing.
In the first round of testing, only one sample was examined to see if the technique would work. It did. Scientists were able to extract DNA, and that DNA gave them the species of the animal that gave its skin. In this case, it was a calf.
Next, five leaves were tested to see if any information about any relationships among skins could be gleaned; for example, were all five taken from the same animal?
The DNA that was extracted from the parchment was mitochondrial DNA. Most other DNA in multicellular organisms is found in the cell nucleus, but mitochondrial DNA is found in the energy-generating organelles in the cells, called the mitochondria.
Mitochondrial DNA is easier to extract from samples, particularly ancient ones, because there are more mitochondria than nuclei and so it stands a better chance of surviving the test of time. But it is only passed down from the mother, so it can reveal maternal relationships, but can't differentiate among individuals.
The mitochondrial DNA taken from Stinson's five pieces of parchment showed that they broke down into one group of two and one group of three. This means that "these have the same maternal lineage in each group," Stinson explained.
In each group it's unlikely that any of the individuals are siblings because cows rarely give birth to twins and bookmakers were unlikely to wait an entire year for another calf to be born to finish their book. So this "means that we have to have at least two individuals."
It's possible that the individuals in each group are first cousins, but it would take nuclear DNA to pin down their full identities.
Getting nuclear DNA from the samples is one of the next steps that Stinson will be pursuing.
He's also working with scientists to develop less invasive testing techniques.
"We can't keep taking plugs of people's manuscripts," he said.
Stinson also wants to broaden the scale of the project by testing many documents of known origin, establishing the relationship among the animals that contributed the parchment and building that out into a database of herds. He plans to focus on a particular area with a few known anchor books "and sort of build out from there," he said.
If the project succeeds, ancient book researchers will have an entirely new tool at their disposal.
"It's a dataset in your hand essentially," Stinson said.