Madgwick et al (2019) used strontium (Sr), oxygen (O) and sulphur (S) isotopes to determine how far pigs had been transported before being consumed at Neolithic sites in Wessex. Strontium is the most reliable indicator of geographical location and depends upon underlying geology. Strontium is incorporated into tooth enamel in young animals and is then fixed for the rest of the animal’s life. The strontium isotope values of a few pigs from some sites showed that they were raised in areas of older rocks (not the chalk found in Wessex). The Sr isotope ratio of bioavailable strontium on the Wessex chalkland is around 0.708, but some pigs had a Sr isotope ratio much higher than this, up to 0.717. There are older rocks in the south of Britain; the Silurian rocks of south wales and the pre-Cambrian rocks of the Malvern Hills have a high ratio, but rocks with a Sr isotope ratio as high as 0.717 are only found in the north of Britain, in the Lake District or some areas of Scotland. This led Madgwick et al to suggest that animals may have been brought from Scotland to Durrington Walls.
In another paper published around the same time, the same group (Evans et al 2019) studied Sr ratios in cattle. They had concluded that some cattle may have been transported from Scotland, but they also raised the possibility that there could be sources of high strontium isotope ratios in the south of Britain that were so far undiscovered. This possibility was raised because other papers had found high strontium isotope ratios in animals and humans that were very unlikely to have been raised in Scotland. However this suggestion was not included in the paper on pigs.
One of the problems with the suggestions that animals were moved around 400 miles before being consumed is the impracticality. It is conceivable that cattle could have been driven along drove roads to get from Scotland to Wessex, but this would have been a journey of several weeks. The return journey would take the total journey into months. Pigs are even more difficult to transport. Pigs cannot be herded like cattle or sheep so driving pigs all that way is highly improbable. Live animals could have been transported by sea but that would be an extremely arduous coastal route that would still involve land transport at each end of the journey. The only other possibility for the transport of live animals is that they were moved by cart. (Is there any evidence for wheeled vehicles in the neolithic?) If they weren’t transported as live animals were they butchered in Scotland and the meat carried to Wessex? Again, unlikely. If the pig had been butchered in Scotland would they really have carried the head all the way to Wessex?
Madgewick et al have been criticised for publicising an unlikely conclusion. Barclay and Brophy (2020), pointed out that strontium isotope ratios up to 0.716 have been found in the Malverns and several places in Wales. Only two pigs out of 131 had ratios above this with a maximum of 0.7172.
Madgwick et al responded by emphasising that their study was a multi isotope study and the results from oxygen and sulphur isotope values support their claim that the pigs could have originated from Scotland. I am not convinced. Oxygen isotope values from pigs are difficult to relate to oxygen isotope values of groundwater and they do not attempt to do this, so cannot identify possible origins of individual pigs. All they can say is that there is a variety of values that must reflect a variety of sources. My biggest problem with this is that pigs are omnivores. They eat anything that is available and if they are fed food waste, how the food has been processed will affect the oxygen isotope values.
Similarly sulphur isotope values cannot be related to specific locations. Generally values are related to the proximity of the sea but the resolution is poor and there is no map that relates sulphur isotope values to location. Again, the authors say that the wide variety of values reflects a variety of origins for the pigs.
To quote directly from Madgwick et al (2019):
On the basis of current mapping data, it is not possible to define origins with confidence, even when using multi-isotope proxies.
Unfortunately, in their abstract they are not quite so cautious and talk about transport pigs “over vast distances”. In their conclusion, based on strontium isotopes, they say that “some of the pigs are likely to derive from Scotland.” I think it is fair to say that their mixed messaging invites criticism.
Overall, the transporting of pigs from Scotland is a very unlikely scenario. There is no doubt that the animals consumed at Stonehenge came from a variety of sources but they most likely came from different sources across southern Britain.
Barclay, G. and Brophy, K. (2020) ‘A veritable chauvinism of prehistory’: nationalist prehistories and the ‘British’ late Neolithic mythos. Archaeological Journal https://www.tandfonline.com/doi/abs/10.1080/00665983.2020.1769399?journalCode=raij20
Evans, J., Parker Pearson, M., Madgwick, R., Sloane, H. and Albarella, U. (2019) Strontium and oxygen isotope evidence for the origin and movement of cattle at Late Neolithic Durrington Walls, UK. Archaeological and Anthropological Sciences 11:5181-5197
Madgwick, R., Lamb, A., Sloane, H., Nederbragt, A., Albarella, U., Parker Pearson, M. and Evans, J. (2019) Multi-isotope analysis reveals that feasts in the Stonehenge environs and across Wessex drew people and animals from throughout Britain Science Advances https://advances.sciencemag.org/content/5/3/eaau6078
Madgwick, R., Lamb, A., Sloane, H., Nederbragt, A., Albarella, U., Parker Pearson, M. and Evans, J. (2021) A veritable confusion: use and abuse of isotope analysis in archaeology, Archaeological Journal https://www.tandfonline.com/doi/full/10.1080/00665983.2021.1911099?scroll=top&needAccess=true#.YKPempqPVqU.twitter
Update, Jan 2023
Recently a more accurate strontium isotope map of south west England has been published, https://the-past.com/news/redrawing-the-strontium-isotope-map-for-the-south-west/ This demonstrates that there are areas in the south west that have higher strontium isotope ratios and that the cattle and pigs found in the Stonehenge area probably came from local sources, not from Scotland, vindicating the above post.