Summary: Dairy products are nutritional resources of global economic importance, and their emergence in prehistory marks a major shift in human dietary ecology. However, basic questions regarding the origins and role of dairying in early human societies remain poorly understood. It is now known that adult hypolactasia (the inability to digest milk sugar) is an ancestral human trait, and that relatively few human populations have genetic variants that allow continued milk digestion into adulthood, a trait known as lactase persistence (LP). The rise of LP has been regarded as a classic example of gene-culture evolution; however, the association between LP and lactose intolerance phenotypes is variable, and LP genotypes do not consistently appear in the archaeological record until more than 5,000 years after the origins of dairying. This has left archaeologists with a puzzling problem, a “milk paradox” regarding how and why ancient peoples developed milk into a dietary resource, how the Bronze Age steppe migrations contributed to the spread of dairying across Eurasia, and what other factors besides LP may have been involved this process. There is now a growing body of evidence that microbes have played important, yet overlooked, roles in the successful establishment of prehistoric dairying economies. This study seeks to answer fundamental questions about the prehistory of dairying by focusing on Mongolia, a country where as much as 80% of the rural diet derives from dairy products, and where dairying has been practiced for more than 3,500 years. Specifically, cutting-edge genomics techniques will be used to identify the origins of Mongolian dairy livestock, proteomics techniques will be used to refine methods for detecting milk proteins in archaeological Mongolian dental calculus, and metagenomics techniques will be used to test hypotheses regarding the relationship between the gut microbiome, lactose digestion, and LP genotypes in nomadic Mongolian dairy herders.
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