They find the oldest direct evidence of milk consumption in Neolithic humans.
A team of scientists at the University of York (United Kingdom) has identified a milk protein called β-lactoglobulin (BLG) in the mineralized dental plaque of seven individuals who lived in the Neolithic period. This is the first direct evidence of milk consumption in adults found worldwide, but this discovery throws up new unknowns.
A mutation that allows you to digest milk
Naturally, the adult human being does not have the capacity to digest milk properly. This is because as the body grows, it stops producing lactase, which is the enzyme responsible for processing lactose. Only those people who carry a genetic mutation known as lactase persistence (LP), keep the gene for this enzyme active and can digest milk throughout their adult life.
However, this evolutionary process should have been very slow, and different evidences suggest that, in the Neolithic, the frequency of people with the LP mutation and the ability to digest milk would still be very low.
It is estimated that one third of the world's population carries LP, with the highest frequencies found in Europe, East Africa, West Africa and the Middle East, where 75% of the adult population can digest milk without problems. In fact, the persistence of LP is considered a very clear example of coevolution between genes and culture, and supports the idea that cultural practices are capable of modifying our genetic code.
The idea is that the Neolithic populations would begin to consume milk as a result of the domestication of animals, ideas that have been supported by various archaeological evidences, for example the discovery of organic residues in Neolithic ceramics that show the presence of various lipids of the milk. The increased dependence on dairy during the Neolithic would have driven natural selection for the LP mutation during the subsequent millennia.
A perfect biomarker
Β-Lactoglobulin is a milk protein that is preserved in human tartar and can be used to detect the consumption of this food in the past. It is only found in milk, and also its amino acids differ between species, making it a perfect biomarker.
The British team, which has published its results in the magazineArchaeological and Anthropological Sciences, analyzed its presence in various individuals who lived in Great Britain during the Neolithic. Furthermore, these samples came from three different archaeological sites, and the results are the oldest evidence found so far for the presence of BLG in human dental plaque.
"The fact that this protein was detected in the tartar of individuals from three different Neolithic sites could suggest that dairy consumption was a widespread dietary practice in the past," reflects Sophy Charlton, one of the researchers participating in the study. How to explain this result if, as we have said, it does not seem that the mutation that allows lactose to be digested was widespread in the Neolithic? The authors believe that these individuals probably still consumed very small amounts of milk, or its derivatives.
"Most of the people who lived in the Neolithic period would have gotten sick from consuming milk, so one explanation could be that these farmers were processing it and obtaining foods with lower lactose content, such as cheese," adds the expert. "Identifying more individuals with BLG can give us more clues about past milk consumption and processing, and increase our understanding of how genetics and culture have interacted to increase lactase persistence in the world," he says.
Another promising line of research would consist of looking for a pattern in milk consumption: "perhaps the amount of dairy products or the animals from which they were obtained also varied according to sex, age or social position", concludes the researcher.
Reference: Charlton et al. 2019. New insights into Neolithic milk consumption through proteomic analysis of dental calculus. Archaeological and Anthropological Sciences. https://doi.org/10.1007/s12520-019-00911-7