The Vikings by all Hollywood accounts enjoyed their grog and meat. Whatever about their drinking habits, excavations at the Wood Quay site at the foot of Christ Church Cathedral, Dublin, did show that they liked their beef.
The site was littered with the remains of feasts past, according to Dr David MacHugh, of the archaeological genetics department at the Smurfit Institute of Genetics, Trinity College. "Bones were some of the most plentiful remains found at Wood Quay."
A collaborative effort involving geneticists and archaeologists from Trinity and Queen's University Belfast set out to determine the origin of these bones. The object of the Wellcome-funded study, Dr MacHugh explained, was to establish whether the animals were brought to Ireland on Scandinavian galleys delivering a taste from home or if they were herded or plundered locally. Their work will be published in the December issue of Philosophical Transactions: Biological Sciences.
Ireland was an ideal location to do ancient DNA work, he said. The climate was conducive for the survival of DNA in archaeological remains, and the bones, dated to just over 1,000 years, were well within the accepted 10,000-year limits for ancient DNA hunters. The bones were taken from soggy riverside soils, but this thwarted biological breakdown, Dr MacHugh said. "They were in anoxic conditions so there was very little bacterial growth or damage."
When the bones were collected in the late 1970s and 1980s they were measured and examined but the ability to study the animals' genetic make-up, their genetic fingerprint, was yet to be introduced, he said.
The team included Dr MacHugh, Mr Chris Troy and the lead author, Prof Dan Bradley, all of Trinity, Dr Finbar McCormick of the School of Archaeology and Palaeoecology at Queen's and support from researchers at the Norwegian College of Veterinary Medicine, Oslo, and the Agricultural Research Institute in Reykjavik, Iceland.
They used the latest genetic techniques including polymerase chain reaction (PCR) amplification of mitocondrial DNA. They compared the DNA in Wood Quay samples with samples collected from modern Irish (including Kerry cows), Norwegian and Icelandic cattle breeds, to determine the origins of the medieval beef.
PCR was a highly demanding method for retrieving DNA, Dr MacHugh said. It could isolate a single DNA fragment and then replicate it a million-fold to a point where its genetic sequence could be studied in detail. Success required elaborate safeguards to protect against accidental contamination, however.
While DNA from the cell nucleus could sometimes be retrieved, ancient DNA hunters frequently isolated DNA from the cell's mitocondria because mitocondrial DNA was more plentiful, Dr MacHugh explained. While there was one nucleus in the cell there could be many hundreds of mitocondria, each offering the possibility of a viable DNA sample. Even so only 11 of the 22 bone samples examined had DNA available for PCR amplification, he said. Generally, the older the bones the lower the success rate.
The bone samples were first sand-blasted to clean away centuries of dirt and contamination and then exposed to strong ultraviolet light to sterilise their surfaces. A bone sample was then taken and powdered and any available DNA was identified and sequenced.
One might have expected the incoming Vikings to have brought some of their own native cattle, but there was no evidence of this in the bones under study, Dr MacHugh said. The new arrivals were happy to take or trade for what was available locally.
The cattle bones recovered at Wood Quay were not far removed genetically from today's animals, however. "They were very similar to modern European cattle. This would suggest that the diversity found in modern cattle arose 5,000 years ago when cattle first appeared in Europe."
However, some level of genetic shift was apparent. The Wood Quay remains "seemed to have some [DNA] sequences that were not present in modern breeds", Dr MacHugh said. These could have been lost through spontaneous change or susceptibility to disease that eliminated certain cattle groups.
The research effort is ongoing with cattle breeds from Spain and Portugal being added for comparison. The 12-strong Trinity group is also examining ancient human DNA and horse and salmon DNA, looking in particular at differences between farmed and wild salmon. Bones from the now extinct ancient Irish elk are also being studied to see if they are related to modern deer.