The beautiful medieval illustrated manuscripts of Europe were carefully inked on parchment; animal hides crafted into something resembling modern paper. Called "uterine vellum,” records hinted it might be made from the hides of calves, sheep, or maybe squirrels and rabbits. And did it really come from a uterus? (Ew.)

In a study published Monday in the Proceedings of the National Academy of Sciences, scientists finally found an easy way to answer your burning questions about uterine vellum. And in the process, they learned a few things about the history of animal husbandry, too.

Figuring out just what this vellum is made of poses a major problem. In order to examine DNA in ancient vellum, researchers have to permanently destroy part of a unique, historic document — or else rely on size, hide thickness, levels of grease, and follicle patterns (ew) to come up with an educated guess for the parchment's origin.

Genetic analysis of Marco Polo’s pocket Bible in 2012 determined it was calfskin, for example, as opposed to fetal lambskin. However, a 5 mg sample of the book presented to Kublai Khan in 1275 was destroyed to make that discovery. Most archivists would faint at the prospect of cutting pieces off precious 700-year-old books to be ground up for analysis.

Researchers needed a way to non-destructively gather proteins from historic vellum. Sarah Fiddyment, a biochemist working in the University of York’s Department of Archaeology, explained, “We had to work with archivists to try and develop a technique that was noninvasive but that could still give us results.”

Fiddyment turned to erasers. Yes, erasers. Polyvinyl Erasers are commonly used by conservationists to clean dirt and stains from parchments. The gentle rubbing creates a triboelectric effect (science translation: a small electric charge) that soils are attracted to. Fiddyment wondered: could some molecules from the manuscript itself be drawn onto the eraser scraps? And could the eraser residue be swept up and analyzed for proteins?

The answer is yes, and with the cooperation of archivists around the globe, she and a group of researchers sampled over 300 vellum documents dating from 1200 to 1819. Peptide mass fingerprinting linked proteins in most of the vellum samples to cows and sheep.

This work not only resolves some scholarly arguments about vellum; it contributes to a separate, larger research project: understanding the genetics of livestock over history.

The large number of samples over a 600-year period let the researchers trace how vellum skins varied geographically over time. Sheepskin is most common in 14th century England, for example. This provides clues to domestication and breeding of livestock, as well as tracing medieval trade in finely crafted animal hides.

“By shedding light on the different animal species used in the production of books in specific areas and periods, the data given by DNA analyses can provide us with a better knowledge about medieval economy as a whole” said Damien Kempf, a medieval historian at the University of Liverpool.

“These are all dated objects, which you don't tend to find in archaeology. Manuscripts are great because they have a very precise date. Being able to attach a genome with an animal to a particular date is incredibly important for us," said Fiddyment.

But wait, you say. Was the uterine vellum actually uterine?

It turns out that monks probably weren't illuminating uteruses. It’s generally been accepted that “uterine vellum” referred to the skins of stillborn animals, not actual uterine walls. The mathematics of just how many uteruses would be needed to supply the output of medieval texts just isn’t practical. Neither is making the books from small animals. Fiddyment said, “Because the parchment is very fine, very thin, people assumed it must be from small animals…We thought, ‘well, realistically, just how many rabbits are we talking about?’"

The authors estimated that a maximum of 200 Bibles/year were created in the 12th century. Assuming an average of 474 pages each, 200 Bibles would be the equivalent of 55,000 rabbits, 27,500 stillborn sheep or goats, 18,000 stillborn calves, or 4,500 young calves or goats. From other sources, they knew that about 306 veal calves were eaten weekly in Paris around that time period. No extreme herd management practices would be needed to meet supply and demand for skins.

As an additional check, the researchers examined proteins found in modern fetal calfskins and young calves, and compared those to a sample from a 200-year-old document they were able to take a small physical sample from. No proteins common in fetal calfskin matched, suggesting that uterine vellum is a name without much connection to actual uteruses or aborted fetuses. For better or for worse, monks were not scrivening away on actual uterine vellum.

Gwen Pearson has a PhD in Entomology and is Outreach Coordinator for the Purdue Department of Entomology. She also blogs for WIRED. You can follow her on Twitter.

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