Milk left a chemical fingerprint in the bones of Neolithic farmers, and researchers are now using calcium isotopes to read it directly from human skeletons for the first time. Archaeologists have long known that early farmers kept cattle and goats, and that they processed milk in pots—traces of dairy fats survive in ancient pottery. But no method could tell whether specific individuals actually drank the milk, or how much. This matters because the ability to digest lactose into adulthood is one of the fastest-spreading genetic traits in recent human evolution, yet the link between milk drinking and the rise of lactase persistence remains untested at the individual level. If the calcium isotope proxy works, it will let researchers measure milk consumption in hundreds of ancient skeletons across Europe and Southwestern Asia. They can then compare those measurements against DNA from the same individuals to see whether milk drinkers were more likely to carry the lactase-persistence gene. The same technique could also reveal whether milk use was underestimated at sites where people used perishable containers instead of pottery. This is primarily fundamental science—it aims to resolve a long-standing question about how a major dietary shift and a genetic adaptation co-evolved. The project also includes a modern component: analysing calcium isotopes in participants from the Children of the 90s study, which could improve understanding of calcium metabolism in living people and inform research on conditions such as artery calcification and osteoporosis.
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Milk and dairy products were introduced relatively recently to the human diet but have had a profound impact on our biology since, with 1 in 3 adults worldwide now being able to digest lactose. Milk production in the past has been assessed through the archaeological study of domesticated animal skeletal elements and the reconstruction of herd management strategies using animal kill-off profiles. Milk use and processing has been inferred through the study of dietary lipids trapped in the ceramic walls of pots during cooking. These methods have provided crucial insights into milk production and use in the past. However, assessing milk consumption in prehistoric populations remains challenging. This project aims to use the calcium isotope signal contained in human skeletal remains to quantify milk consumption at the individual level and explore the links between milk consumption and ecological, nutritional, cultural and genetic factors in the early farming communities of Europe and Southwestern Asia. To achieve this, we will first calibrate the relationship between the calcium isotope composition of diet and consumer tissues using calcium-containing foodstuffs, modern humans from a birth cohort longitudinal study (ALSPAC, known as Children's of the 90s study) and an animal model (pigs). We will then use this calibration to quantify milk consumption in past populations via the analysis of ancient human skeletal remains. We will target populations from the Pre-Pottery Neolithic (PPN) to investigate the dietary shift immediately following animal domestication. Post-PPN populations will also be studied to understand milk consumption at sites where perishable containers may have been used for milk processing and thus where the analyses of dietary lipids preserved in pottery vessels may have underestimated milk use. Finally, we will target genotyped archaeological individuals from Europe and Southwestern Asia to test the link between the presence of lactase persistence alleles and milk consumption. This project will aim to test, using a model comparison framework, the link between milk consumption and ecological, nutritional, cultural and genetic factors. This project is highly interdisciplinary, with environmental chemistry, archaeology, genetics, and epidemiology at its heart. This research will provide a novel proxy for milk consumption in ancient populations that is complementary to lipid residue analyses of pottery sherds, thus expanding the compendium of diet-informative isotopes. The project will reveal - for the first time - the individual-level correspondence between prehistoric milk consumption and lactase persistence, and so provide an 'as it is happening' perspective on the evolution of the most advantageous monogenic human trait to have evolved in the last 10,000 years. Our study of modern populations from the ALSPAC study will increase our understanding of calcium homeostasis in human populations, opening the way to studies on Ca-related health issues, e.g. artery calcification and osteoporosis.
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