Ancient DNA adds a twist to the story of how barnyard chickens came to be, finds a study to be published April 21 in the journal Proceedings of the National Academy of Sciences.
Analyzing DNA from the bones of chickens that lived 200-2300 years ago in Europe, researchers report that just a few hundred years ago domestic chickens may have looked far different from the chickens we know today.
The results suggest that some of the traits we associate with modern domestic chickens -- such as their yellowish skin -- only became widespread in the last 500 years, much more recently than previously thought.
"It's a blink of an eye from an evolutionary perspective," said co-author Greger Larson at Durham University in the United Kingdom.
The study is part of a larger field of research that aims to understand when, where and how humans turned wild plants and animals into the crops, pets and livestock we know today.
Generally, any mutations that are widespread in domestic plants and animals but absent from their wild relatives are assumed to have played a key role in the process, spreading as people and their livestock moved across the globe. But a growing number of ancient DNA studies tell a different tale.
Chickens are descended from a wild bird called the Red Junglefowl that humans started raising roughly 4,000-5,000 years ago in South Asia. To pinpoint the genetic changes that transformed this shy, wild bird into the chickens we know today, researchers analyzed DNA from the skeletal remains of 81 chickens retrieved from a dozen archeological sites across Europe dating from 200 to 2,300 years old.
The researchers focused on two genes known to differ between domestic chickens and their wild counterparts: a gene associated with yellow skin color, called BCDO2, and a gene involved in thyroid hormone production, called TSHR.
Though the exact function of TSHR is unknown, it may be linked to the domestic chicken's ability to lay eggs year-round -- a trait that Red Junglefowl and other wild birds don't have.
When the team compared the ancient sequences to the DNA of modern chickens, only one of the ancient chickens had the yellow skin so common in chickens today. Similarly, less than half of the ancient chickens had the version of the TSHR gene found worldwide in modern chickens.
The results suggest that these traits only became widespread within the last 500 years -- thousands of years after the first barnyard chickens came to be. "Just because a plant or animal trait is common today doesn't mean that it was bred into them from the beginning," Larson said.
"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," he added.
"…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."
- Flink, L., et al. Establishing the validity of domestication genes using DNA from ancient chickens. PNAS, 2014 DOI: 10.1073/pnas.1308939110
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