The lambs break their silence

A study of ancient bones shows that Early Neolithic sheep-breeders were faced with high levels of mortality among young animals in their herds. A statistical model, partly developed at Ludwig-Maximilians-Universitaet (LMU) in Munich, allowed the age distribution of the bones to be precisely determined.

In the 8th millennium BCE, early sheep-herders were already aware that the conditions under which their animals were housed had an impact on mortality rates among the lambs. This one result of a study researchers led by Nadja Pöllath (a curator at the State Collection for Anthropology and Palaeoanatomy in Munich), LMU zooarchaeologist Joris Peters (who is also the Director of the state collection) and LMU statistician Sevag Kevork have now taken a closer look at the bones of unborn and neonatal lambs, which form part of the collections studied by them. The material comes from the Early Neolithic site Aşıklı Höyük, one of the largest and best investigated settlements from this period in Central Anatolia. The site was occupied from 8350 to around 7300 BCE, and the study reveals that the life expectancy of newborn lambs gradually increased over this timespan. The researchers attribute this finding to improvements in husbandry of the herds, which enabled a larger proportion of neonates to survive the nursing period, and be let out to graze the nearby pastures.

The archaeological remains that have come to light at Aşıklı Höyük provide valuable information, not only on its domestic architecture and cultural practices, but also on the surrounding vegetation and the diets of the people and animals living in the area. Moreover, it sheds light on the development of agriculture and animal husbandry during the Early Neolithic period. The finds indicate that, in the settlement’s earliest phase, its inhabitants still obtained their meat mainly from hunting. Later on, however, domesticated animals – primarily sheep – supplied much of the animal protein consumed. The discovery of compacted dung layers within the settlement indicates that sheep were kept for longer periods within the boundaries of the settlement.

A new analysis of the age distribution of the animal bones found at Aşıklı Höyük illustrates the problems with which early sheep-herders were confronted – and on how they learned to mitigate them. Most of the conventional approaches used to determine the exact age at which the animals died focus on teeth. However, such methods are not sufficiently sensitive to enable researchers to reliably differentiate between developmental stages in very young animals – in this case, sheep covering the age range from the fetus to newborns and juveniles.

In order to determine the ages of fetuses and lambs as accurately as possible, the researchers developed a new statistical model. They first analyzed the morphology of the humerus or upper-arm bone in a sample of modern sheep breeds, based on material kept in anatomical reference collections in the US, the UK, Spain, Portugal and Germany, and used the results to construct a comparative model for Neolithic sheep. In this way, the age at death of the bones of lambs from Aşıklı Höyük could be precisely determined. “Our analyses were of great value in enabling us to narrow down the range of possible ages of death in fetuses and lambs,” says Nadja Pöllath. “We now have a better understanding of the difficulties that early herders faced in the early phases of sheep domestication in Aşıklı Höyük.” Infections were the primary causes of early mortality, together with malnutrition and dietary deficiencies. In addition, the animals were kept under overcrowded conditions. When they were subsequently let out to grass their health improved. The zooarchaeological data also suggest that, towards the end of the occupation of Aşıklı Höyük, fetal mortality fell and more lambs survived. Prof. Peters concludes: “Our research thus proves for the first time that learning by doing determined the early phase of livestock farming in the 9th and 8th millennia BCE.”

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