We may now know when chickens were domesticated – but not why

The earliest domestic chickens we have ever found lived no earlier than 3670 years ago, suggesting the world’s most common domestic animal has a far shorter history than previously thought. What is more, these birds don’t appear to have been raised for their meat, making it unclear what drove the domestication process.

The chickens alive today descend from a wild bird native to South-East Asia called the red junglefowl (Gallus gallus), but exactly when domestication occurred was unclear. Some researchers have estimated that the first domestic chicken lived more than 6000 years ago, while others claim to have found chicken bones at 10,000-year-old archaeological sites.

Ophélie Lebrasseur at the Centre for Anthropobiology and Genomics of Toulouse in France has co-authored a comprehensive analysis of the evidence. It concludes that domestic chickens make their first clear appearance in the archaeological record much later – between 1650 BC and 1250 BC at a site called Ban Non Wat in central Thailand.

“It’s the earliest irrefutable evidence,” says Lebrasseur. Not only are chicken bones superabundant at Ban Non Wat, there is also evidence that people were buried with the birds, which she says makes a domestic relationship clear.

One reason why researchers had previously suggested domestication occurred much earlier is that chicken bones are easily confused with those of other birds, such as pheasants. Another reason is that burrowing animals can displace small chicken bones underground so that they end up in older, deeper layers of dirt, which can lead archaeologists to assume the bones are ancient.

In a second study, Julia Best at Cardiff University, UK, and her colleagues showed how this process can confuse archaeologists. They radiocarbon-dated 23 chicken bones from several archaeological sites across Europe and north-west Africa, and found 18 of them were younger than previously thought.

One bone from a site in Bulgaria had been estimated to be 7500 years old – but radiocarbon dating suggested it belonged to a chicken that was alive between about 1959 and 1985. Best says such results weren’t entirely unexpected. “We had begun to have an inkling that some of the earliest bones were probably not as ancient as had been claimed,” she says.

Lebrasseur’s team suspects chicken domestication might have been triggered by the appearance of cereal farming in South-East Asia. “This created a more open, less [tree-covered] environment, which is actually an environment where red junglefowl thrive,” she says. “And they could have fed on the waste from human societies.”

This suggests the birds were attracted to human settlements, and natural selection might have played a role in turning them into domestic chickens. Dog domestication is thought to have occurred in a broadly similar way.

Why humans would have encouraged chicken domestication is less clear. Best and her colleagues found little evidence that chickens were butchered for their meat when they were first introduced to Europe, and Lebrasseur thinks this indicates domestication wasn’t driven by a desire for meat. She says we still don’t really understand what drove the process. Perhaps early chickens acted as alarm systems, just as geese can, or perhaps they were kept for their eggs.

Which came first, the chicken or the egg?

Eggs evolved more than a billion years ago, whereas chickens have been around for just 10,000 years. So the riddle is easily solved…or is it?

What we do know is that chickens were generally seen as exotic animals, particularly once they spread beyond the red junglefowl’s natural geographic range. With their radiocarbon dating, Best and her colleagues could see that the earliest chickens in Europe – which date to the first millennium BC – were often carefully buried rather than being casually butchered.

Human-chicken co-burials in Britain about 2000 years ago might be evidence that the birds were viewed as spiritual guides that could lead human souls into the afterlife, says Best. “There were some associations with deities.”

In Europe, it was only a few centuries after their introduction that chickens found their way onto the dining table and their status fell. Ultimately, human societies came to consider it acceptable to raise chickens under intensive conditions. But Lebrasseur thinks the recent trend towards free-range chicken shows that some consumers do now care a little more for chicken welfare. “It’s an interesting shift,” she says. “There is a conscious consumer choice now to select chickens that have been better treated.”

Journal references: PNAS, DOI: 10.1073/pnas.2121978119, and Antiquity, DOI: 10.15184/aqy.2021.90

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