Earliest evidence of loss of seasonal egg laying in chickens

While some of us are still asking “why did the chicken cross the road?” an international team of researchers has been answering a different question: when did humans begin raising them for eggs?

In a new paper published in Nature Communications, scientists have presented the earliest clear evidence of people raising chickens for egg production from approximately 400 BCE.

The researchers argue that it was a change from seasonal egg laying to more prolific egg production that drove the domestic chicken’s dispersal across Eurasia and northeast Africa.

“This is the earliest evidence for the loss of seasonal egg laying yet identified in the archaeological record,” says Dr Robert Spengler, leader of the Domestication and Anthropogenic Evolution research group at the Max Planck Institute of Geoanthropology, Germany, and principal investigator on the study.

“This is an important clue for better understanding the mutualistic relationships between humans and animals that resulted in domestication.”

The research team collected tens of thousands of eggshell fragments from archaeological sites along the main Central Asian corridor of the Silk Road. Using a method of biomolecular analysis known as ZooMS (Zooarchaeology by mass spectrometry) they were able to identify the source of the eggs.

ZooMS identifies animal species from remains such as bone, teeth, skin, antler, and egg by characteristic sequences of amino acids in the protein collagen. Because ZooMS relies on protein signals rather than DNA, this makes it a faster and more cost-effective option than genetic analysis.

“This study showcases the potential of ZooMS to shed light on human-animal interactions in the past,” says Dr Carli Peters, a researcher at the Max Planck Institute of Geoanthropology and first author of the new paper.

The results of their analysis shows that chickens were widely raised in Central Asia from approximately 400 BCE to 1000 CE and were likely dispersed along the ancient Silk Road. 

The abundance of eggshells throughout the sediment layers at each site also indicate the birds must have been laying out of season and more frequently than their wild ancestor, the red jungle fowl, which nests once per year and typically lays six eggs per clutch.

It was this trait of prolific egg laying, the researchers argue, that made the domestic chicken so attractive to ancient peoples.

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