Sorting the sheep from… the other sheep

Continuing this blog’s impromptu ‘DNA season’, I’d like to flag up another recent article. Now this is ingenious stuff. It made me chuckle with admiration, in an I-wish-I’d-thought-of-that sort of way.

First, the problem: historic livestock. How can we know what breeds of livestock were kept in the past? How far back can we trace so-called ‘heritage breeds’? For more recent periods of history, there might be realistic paintings or detailed descriptions that allow us some insight, but such sources will get much less reliable the further back we go. By the medieval period at least, we’d be skating on very thin ice. What about the evidence of animal bones? True, that’s extremely useful. Skeletal remains can allow a specialist to calculate the original size of animals (withers heights, etc.). This can allow the identification of selective breeding –  but only if the farmers were selecting for size. Potentially more information could be acquired by extracting aDNA (ancient DNA) from the animal bones, but these are usually far too degraded to allow any such thing. In most cases, after all, they’ve been butchered, gnawed, and thrown away.

That’s where parchments come in. Documents have been written on animal-hide parchment for centuries and, although they’re not guaranteed to survive forever, it’s safe to say that they won’t usually be gnawed or butchered. Indeed, because they often have legal value, a great number have been carefully curated over the centuries. In Britain alone, it’s estimated that more than a million parchments may survive from the last millennium. And now it’s been demonstrated that they can be used as a good source of livestock aDNA. Researchers from Dublin and York have done a pilot project, successfully getting verifiable aDNA from tiny samples of sheepskin parchment from the 17th and 18th centuries.

The Past Horizons website has a good summary.

Not only that, but the original research is published in an open access article, free for anyone to read and download:

Teasdale, M.D., van Doorn, N.L., Fiddyment, S., Webb, C.C., O’Connor, T., Hofreiter, M., Collins, M.J., & Bradley, D.G. (2015). ‘Paging through history: parchment as a reservoir of ancient DNA for next generation sequencing’, Philosophical Transactions of the Royal Society B, volume 370.

From the two parchments that they analysed, they suggest a speculative interpretation: that one represents an ‘unimproved’ sheep breed (i.e. closer to its natural progenitor) and the other a selectively ‘improved’ breed: potentially, we have here a major new tool to explore how livestock changed during the era of agricultural improvement in England – and of course other periods and places too, if the material survives.

Oh, and if curators don’t mind samples being trimmed from their parchments.

MJM.

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