Wednesday, June 8, 2022

Chicken Domestication

New article in PNAS:

Though chickens are the most numerous and ubiquitous domestic bird, their origins, the circumstances of their initial association with people, and the routes along which they dispersed across the world remain controversial. In order to establish a robust spatial and temporal framework for their origins and dispersal, we assessed archaeological occurrences and the domestic status of chickens from ∼600 sites in 89 countries by combining zoogeographic, morphological, osteometric, stratigraphic, contextual, iconographic, and textual data. Our results suggest that the first unambiguous domestic chicken bones are found at Neolithic Ban Non Wat in central Thailand dated to ∼1650 to 1250 BCE, and that chickens were not domesticated in the Indian Subcontinent. Chickens did not arrive in Central China, South Asia, or Mesopotamia until the late second millennium BCE, and in Ethiopia and Mediterranean Europe by ∼800 BCE. To investigate the circumstances of their initial domestication, we correlated the temporal spread of rice and millet cultivation with the first appearance of chickens within the range of red junglefowl species. Our results suggest that agricultural practices focused on the production and storage of cereal staples served to draw arboreal red junglefowl into the human niche. Thus, the arrival of rice agriculture may have first facilitated the initiation of the chicken domestication process, and then, following their integration within human communities, allowed for their dispersal across the globe.

Since Indian archaeologists have claimed domesticated chicken remains as old as 6,000 BC, this is not going to be accepted without a fight. Nor should it be; the study of dog and horse domestication has shown that different approaches can produce widely divergent results – for dogs, c. 15,000 years ago vs. 33,000 years ago – using arguments that seem compelling on their own terms.

An earlier spread of domesticated chickens has also been used to explain a bunch of odd evidence, for example an Egyptian text from 1450 BC that mentions "the bird that gives birth every day." If those weren't chickens, that leaves unanswered questions.

This new result is one of dozens flowing from improved radiocarbon dating. Many old dates are wrong because things buried in the ground get contaminated. For example, these authors say that one chicken bone from Morocco with an ancient date was actually a modern bone that came into contact with old material; what was on the outside of the bone had nothing to do with the bone itself. Using modern methods, a lab can take that same bone and extract purified bone collagen from it, a tiny amount to be sure but enough to produce a radiocarbon date that almost certainly relates to the bone itself.

Besides the redating, these authors also say that chickens were not initially domesticated for food. The early bones come from ritual contexts, not trash dumps, and they are complete birds rather than cut up bones. One theory is that chickens served as alarms and were treated as guardian spirits. Another is that they were initially used for cockfighting, which may have had some ritual function. Or maybe they were just pets; people all over the world still do that.

When I was growing up I read a lot of very confident statements about animal domestication, as if the questions had all been answered, but that has turned out not to be true at all.

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