Although scientists have long known that settlers of prehistoric Britain kept domestic animals, it was uncertain whether these animals were raised primarily for their meat or for secondary products such as wool or milk.

Seeking chemical evidence to solve the puzzle, Dr Mark Copley and colleagues in the University's School of Chemistry collected potsherds - the broken, dirty dishes of ancient civilisations - from several archaeological sites in Britain settled during the Neolithic, Bronze Age, and Iron Age.

The researchers examined each sherd for evidence of fats from milk or meat. Although the fats are chemically very similar, milk fats contain different ratios of the stable isotopes of carbon (carbon-12 and carbon-13), compared to meat fats.

Residues on potsherds from each site indicated the presence of dairy products. However, the age of sherds containing milk residues differed from site to site, a factor that points to the gradual spread of dairying practice throughout Britain with time.

Of particular interest were three sites with dairy sherds from the Neolithic era, a period in which dairy use had previously been uncertain. The researchers suggest that the widespread availability of dairy products may have had major impacts on ancient peoples' diet, health, and subsistence economy.

The paper The Earliest Direct Chemical Evidence for Widespread Dairying in Prehistoric Britain by Dr Mark Copley, Professor Richard Evershed and others will be published in the Proceedings of the National Academy of Sciences (PNAS) of the United States of America, week commencing 27 January 2003.