Thursday, June 21, 2012

Earliest evidence of dairying practices in Sahara found

Researchers from the University of Bristol and other institutions have found the “first unequivocal” chemical evidence of dairying practices by Saharan people about 5,000 years ago — at a time when the region was in a humid phase and had plenty of plant cover. The story so far Researching the earliest evidence of dairying has so far been confined to Europe, Near East and Eurasia. This is the first time an attempt is made to study African samples. The results are published today (June 21) in Nature. Till date evidence of domestication of cattle, sheep and goats came from faunal samples. But faunal remains have been “highly fragmentary and poorly preserved.” Reconstructing evidence of herding has therefore been difficult. Even indirect evidence of dairying is “missing.” Of course, rock paintings and engravings have provided some compelling indirect evidence. The researchers therefore turned to molecular and isotope analysis of absorbed food residues found on potsherds to know the details. The rationale is simple: analysing food residues is a sure way of understanding diet and subsistence practices of humans a few thousand years ago. Making the study possible has been the exemplary preservation of absorbed organic residues, particularly lipids, on potsherds. This is unlike in the case of European sites where only 40 per cent of potsherds provided any evidence of lipids, and that to at very low concentrations. “This remarkable preservation [in the case of African samples] is likely to be related to the extremely arid conditions prevailing in the region” in the last hundreds of years. The researchers used carbon 13 isotopic ratios to study the major alkanoic acids of milk fat. The lipids belonged to three categories — “high abundance” of C16:0 and C18:0 (lipid numbers) fatty acids derived from degraded animals fats. There were carbon isotopes (C13 to C18) which are demonstrative of “bacterial origin” and diagnostic of “ruminant animal fats.” In the second category, the carbon isotopes found were diagnostic of plant oils and a certain kind of wax of vascular plants. The third type of residue indicates the “drying reaction of plant oils,” and reflects either “processing of both plant and animal products in the same vessel or the multiuse of the vessels.” Of the three types, only those indicative of degraded animal fats were taken up for detailed analysis. Compared with present day animal fats, about 50 per cent of lipid samples recovered from the potsherds fall within or on the edge of isotopic range of dairy fats. About 33 per cent fall within the isotope range for ruminant adipose fats. “The unambiguous conclusion is that the appearance of dairy fats correlates with the abundant presence of cattle bones in the cave deposits, suggesting a full pastoral economy,” they write. They also found unequivocal evidence for “extensive processing of dairying products” in pottery in the Libyan Sahara between 5,200-3,800 years ago. This confirms that “milk played an important part in the diet of these prehistoric pastoral people.” This is quite surprising considering the fact that these people were able to consume milk despite suffering from lactose intolerance. The study thus provides a window to the “evolutionary context for the emergence of lactase persistence in Africa.”

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