Issue 91

November/December 2006

Contents

news

New finds 30 years on from the drought of 76

Houses near Stonehenge astonish archaeologists

Roman pool may be for early Christian baptism

Logboat's last voyage launches new journey

In Brief

features

English landscape: lovely, isn't it? It's dead
Cider with trunk roads - Trevor Rowley casts an archaeological eye on the last century

Final proof of ancient UK contact with Sicily?
Salcombe and Dover - Bronze age wrecked cargoes in Devon and Kent

Science: evidence for ancient dairying
Neolithic farmers milked their animals in 4000BC

on the web

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ISSN 1357-4442

Editor Mike Pitts

science

Old English yogurt

Sebastian Payne, chief scientist at English Heritage, finds another unexpected way of learning about the past.

In a recent project, on which English Heritage joined Richard Evershed of Bristol University and others, we discovered that milk can be identified in English neolithic potsherds¹. The survival of degraded fats in unglazed sherds that are thousands of years old is surprising. One might expect that fats would be broken down by bacteria and other agents of decay very quickly after pots are discarded, and that we would only find fat traces in exceptional preservation conditions. But recent advances allow us to detect and identify organic compounds in very low concentrations: we found traces of degraded fats in over 50% of neolithic (4000–2200BC), bronze age (2200–800BC) and iron age (800BC–AD43) pot sherds from southern England.²

Presumably these degraded fats have been protected from microbial attack by being absorbed into the fired clay. They typically include relatively large amounts of two long-chain fatty acids: palmitic acid and stearic acid. Both occur in plant and in animal fats, but palmitic acid is much commoner in plant fats, and stearic acid in animal fats. In most of these prehistoric sherds stearic acid is much commoner than palmitic, suggesting the fats come mainly from animals.

Ruminants (such as cattle, sheep and goats) have unusual digestive systems in which stomach bacteria break down plant cellulose in a kind of double fermentation. Recent research has shown that the fats in ruminants, though made up of the same fatty acids, differ from fats in other animals (including people, pigs and horses) in the ratio of the two stable carbon isotopes: ruminant carcass fats have less of the heavy 13C isotope. During lactation some fats are routed in a different way and have even less 13C. So unusually low proportions of 13C suggest ruminant milk fats.

Pots probably had many different uses, so the isotope ratio in the stearic acid from one pot can reflect mixed use. But what is particularly interesting about the stearic acid from these English prehistoric pots is that in many cases the isotope ratios are those characteristic of ruminant milk.

Could these results be misleading, produced by the effects of burial? If decay has altered the ratios to any large extent, one would not expect the ratios from the pots to fall, as they do, inside the range expected from mixtures between pork, ruminant meat fat and ruminant milk fat. Experiments have shown that isotope ratios are not significantly changed by burial and decay.

The evidence for the widespread use of milk in the neolithic in England seems remarkably strong. Sex ratios and killing ages in contemporary animal bone assemblages, while not by themselves conclusive, tend to the same conclusion.

People have doubted that milk was consumed at an early stage of animal domestication, because in most human populations raw milk causes digestive problems in most adults: they have lost the ability – present in small children – to digest lactose, the sugar in milk. Butter, cheese and yoghurt, containing little or no lactose, cause fewer problems.

Burial trials show that fats from raw milk decay much faster than butter, probably because the sugars and less stable fats in milk encourage rapid bacterial attack and decay. If neolithic people were already processing milk into other products, this would explain why milk fats survive relatively commonly in neolithic pots. It would also have made it possible to avoid the lactose problem and to store milk products. It may be that milk was one reason why sheep, goats and cattle were domesticated.

More science

1 MS Copley et al in Antiquity 79 (2005), 895–908; MS Copley et al in Proceedings of the National Academy of Sciences 100 (2003), 1524–9
2 MS Copley et al in Journal of Archaeological Science 32 (2001), 485–546

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