The real chicken mystery has nothing to do with whether the egg came first. Scientists would like to know when, where and how a bird of the jungle came together with human farmers to begin down the path that eventually led to the Popeyes chicken sandwich.
The more bioarchaeologists and evolutionary biologists delve into the deep past of the chicken, the more complex its history becomes, and the more difficult it is to imagine a time when they were not food. But recently, scientists have been reconstructing a past in which the birds, descendants of the red jungle fowl, were first viewed by humans as marvelous and exotic, then sometimes sacrificed to ancient gods and sometimes revered as status symbols.
Details of when and where the chicken was domesticated were debatable. The picture that had emerged was one of early domestication 8,000 or more years ago, possibly in China or India or Southeast Asia. But a pair of companion articles released Monday in the journals Proceedings of the National Academy of Sciences and Antiquity offered an updated origin story, putting the emergence of the domestic chicken closer to 3,500 years ago in what is now Thailand.
The reports also propose a new hypothesis for how domestication occurred. The researchers argue that the first archaeological evidence of domestic chickens coincides with the advent of rice and millet cultivation in dry fields that attract the jungle fowls, bringing them out of the forest into regular contact with people.
In combination, the reports make the case for a “comprehensive re-evaluation of chickens” and demonstrate “how wrong our understanding of the time and place of chicken domestication was,” said Greger Larson, a specialist in domestication and ancient DNA at Oxford University who was an author on both papers.
In the report in the Proceedings, researchers re-evaluated the evidence from more than 600 sites in 89 countries and found the earliest fossils of domestic chickens at a stone age site, Ban Non Wat, in central Thailand. The bones were about 3,500 years old.
The study also found that chickens spread west to Africa with seafaring traders from Southeast Asia, and then eventually north into Europe. Previous estimates of chickens reaching Europe 7,000 years ago did not hold up. Instead, the researchers estimate that chickens first reached Southern Europe 2,800 years ago. It took hundreds of years to reach more northern areas and a full millennium to reach Scandinavia and Scotland.
Joris Peters of Ludwig Maximilian University in Munich, an author on the paper in the Proceedings, said that the study “rewrites the origins and history of poultry husbandry.”
The report in Antiquity was based on radiocarbon dating of 23 samples of chicken bones from North Africa and Europe, many of which had been previously studied. It showed that three quarters of the fossils had been wrongly dated. In some cases, as in one in Morocco, modern chicken remnants (from 1950 or later) had been dated to the Iron Age.
Julia Best, an author on the report, said that with radiocarbon dating rather than geological and archaeological methods, “We now have the clearest picture yet of our early interactions with chickens.”
Some patterns of how ancient people treated chickens became clear with the method. In Britain and at European Iron Age sites, the researchers found adult chickens buried alone with no signs of butchery, one even with a healed leg fracture, which suggested human care.
It seems humans did not begin by eating the birds, but by admiring their charismatic and exotic presence. As the chicken spread around the globe with extraordinary speed, every human group seemed to treat it with reverence.
Naomi Sykes, at the University of Exeter in England and an author on both papers said, “for centuries chickens were celebrated and venerated.” Only later did we start eating them regularly.
Even when the birds arrived in a new location, the evidence suggested that it took a few hundred years of living with chickens to get to know them well enough to begin eating them regularly. When Romans invaded Britain, they were eating the birds, while the Britons were not.
Olivier Hanotte, a specialist in animal genomics at the University of Nottingham in England and the International Livestock Research Institute, said that the articles provided a “really good analysis of all the data.” Dr. Hanotte, who recently participated in an analysis of chicken ancestry along with Dr. Larson and others but was not involved with either of the two new papers, said the latest studies demonstrated that the domestication of chickens was more recent and spread very rapidly around the world. “So we should really not be saying that the domestication was so ancient.”
However, he was not completely convinced by the domestication hypothesis offered in the paper, which the authors acknowledged would require further research to confirm. He said that in many societies, children kept wild animals as pets. That could have been a precursor to domestication, he said, and would leave few traces.
Dr. Larson said the new hypothesis was valuable because ideas about domestication have too often concentrated on human actions and intent. First, he said, researchers need to look for a situation in which the animals derive some benefit from association with humans.
The authors said the pattern of dry rice cultivation present in Thailand 3,500 years ago, with large productive and fallow fields and bordering thickets, may have been a better niche for jungle fowl than the irrigated paddies common in other areas.
“And that kicks off this relationship,” Dr. Larson said.