Direct chemical evidence for widespread dairying in prehistoric Britain

Abstract

Domesticated animals formed an important element of farming practices in prehistoric Britain, a fact revealed through the quantity and variety of animal bone typically found at archaeological sites. However, it is not known whether the ruminant animals were raised purely for their tissues (e.g., meat) or alternatively were exploited principally for their milk. Absorbed organic residues from pottery from 14 British prehistoric sites were investigated for evidence of the processing of dairy products. Our ability to detect dairy fats rests on the observation that the delta(13)C values of the C(18:0) fatty acids in ruminant dairy fats are approximately 2.3 per thousand lower than in ruminant adipose fats. This difference can be ascribed to (i) the inability of the mammary gland to biosynthesize C(18:0); (ii) the biohydrogenation of dietary unsaturated fatty acids in the rumen; and (iii) differences (i.e., 8.1 per thousand ) in the delta(13)C values of the plant dietary fatty acids and carbohydrates. The lipids from a total of 958 archaeological pottery vessels were extracted, and the compound-specific delta(13)C values of preserved fatty acids (C(16:0) and C(18:0)) were determined via gas chromatography-combustion-isotope ratio mass spectrometry. The results provide direct evidence for the exploitation of domesticated ruminant animals for dairy products at all Neolithic, Bronze Age, and Iron Age settlements in Britain. Most significantly, studies of pottery from a range of key early Neolithic sites confirmed that dairying was a widespread activity in this period and therefore probably well developed when farming was introduced into Britain in the fifth millennium B.C.

Figure 1

(a) Histogram of the δ¹³C values of C_18:3 fatty acid and glucose extracted from plants. The histogram demonstrates that there is an 8.1‰ mean difference in the δ¹³C values of C_18:3 fatty acid (mean = −36.3‰) and glucose (mean = −28.2‰), and these isotopic differences are known to result from fractionation during the formation of acetylCoA (21). (b) Diagram showing the routing of dietary fatty acids and carbohydrates in the rumen, adipose tissue, and mammary gland of the ruminant animal. Approximately 60% of the C_18:0 in ruminant milk appears to be directly incorporated from the diet, after biohydrogenation of unsaturated fatty acids (e.g., C_18:3) in the rumen (*) and reflects the inability of the mammary gland to biosynthesize C_18:0 (19, 20). The difference in the δ¹³C values of C_18:0 in ruminant adipose tissues and dairy fats can also be seen graphically in Fig. 2.

Figure 2

(a) Plot of the difference in the δ¹³C values of the C_18:0 and C_16:0 fatty acids (=Δ¹³C value) obtained from the modern reference fats. The mean and 2 SD are depicted and demonstrate that the animal fats are also distinguished by using this criterion. (b) Plot of the δ¹³C values of the major fatty acid components (C_16:0 and C_18:0) of modern reference fats. The three fields correspond to P = 0.684 confidence ellipses calculated for the δ¹³C values of the domesticates known to comprise the major component of prehistoric economies in Britain. All of the animals were raised on C₃ diets. The δ¹³C values obtained from the modern reference materials have been adjusted for post-Industrial Revolution effects of fossil fuel burning by the addition of 1.2‰ (31). Analytical precision is ±0.3‰.

Figure 3

Plots of the δ¹³C values of the major fatty acid components (C_16:0 and C_18:0) and the Δ¹³C values of lipid extracts from potsherds from the Neolithic sites of Windmill Hill (a), Hambledon Hill (b), and Eton Rowing Lake (c). The fields and ranges corresponding to the modern reference fats (see Fig. 2) serve to classify the lipid extracts. Extracts that plot between the reference ellipses are indicative of the mixing of commodities in antiquity.