Modern Chickens Are Quite Young, Originating Only About 500 Years Ago
Your barnyard chicken looks very different from what your ancestors may have eaten 1,000 years ago. This was the conclusion scientists arrived at after studying the DNA of bones from chickens that lived 200 to 2,300 years ago in Europe.
Published in the Proceedings of the National Academy of Sciences, the scientists' study suggests that some traits like the yellowish skin of modern day chickens may have developed within the past 500 years or so, which is quite recent in terms of evolutionary history - the "blink of an eye from an evolutionary perspective," said co-author Greger Larson, from Durham University, UK, in a press release.
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Learning about the evolution of barnyard chickens is part of an ongoing study that attempts to answer how humans came to domesticate wild plants, animals, and birds as we know them today. For many years, evolutionary scientists have assumed that a genetic mutation present in domestic plants and animals, but absent in their wild counterparts, may have been responsible for domestication - spreading through livestock as humans spread geographically. But these stereotypes have been challenged by recent studies of ancient DNA.
For example, the domestic chicken are known to have descended from the Red Junglefowl now found mostly in Asia. This wild bird was first domesticated around 4,000 to 5,000 years ago in Asia, and then taken around the world. To understand the genetic mutations that transformed this wild bird into the modern day chicken, scientists analyzed the bones of 81 chickens retrieved from a dozen archaeological sites across Europe.
The researchers focused on two genes that are found in domestic chicken but not in the wild versions. The first gene, called BCDO2, is responsible for their skin's yellow color, while the second gene, TSHR, is involved with thyroid hormone production. Besides hormone production, TSHR is also believed to be responsible for the domestic chicken's ability to lay eggs throughout the year - a trait not found in wild birds, including the Red Junglefowl.
When the team compared the ancient DNA sequences to those of modern chickens, only one of the ancient chickens had the yellow skin so common in chickens today. Similarly, a version of the TSHR gene - present in all modern chickens - was found in less than half of the ancient chickens. Thus, the researchers concluded that these traits only became widespread within the last 500 years, thousands of years after the first barnyard chickens appeared.
"Just because a plant or animal trait is common today doesn't mean that it was bred into them from the beginning," Larson said in the release. "It demonstrates that the pets and livestock we know today - dogs, chickens, horses, cows - are probably radically different from the ones our great-great-grandparents knew."
So how do their appearances change so drastically? Larson said that "they are subjected to the whim of human fancy and control, [so] radical change in the way they look can be achieved in very few generations."
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