The most likely wild chicken ancestor, photographed in India.

More than 10,000 years ago, our ancestors began to expand their organization offood productionpurposefully promoting certain plants and animals they found tasty or useful. Over time, they domesticated those species, inserting human preferences into the process of natural selection.

We know today that agriculture and domesticated species arose separately in different regions around the world. Grains, beans, and livestock appear to be some of the earliest species domesticated in Southwest Asia, for example. But many questions remain about why humans shifted from hunting and gathering to agriculture and how the process of domesticatingspecies unfoldeda process that, in cases like wheat and rice, appears to have taken more than a thousand years.

A special section in this weeks Proceedings of the National Academy of Sciencesdelvedinto what science has discovered about domestication and how toprovide answers to ourremaining questions about the lives of prehistoric people and their relationship with the plants and animals around them.

In one of the examples explored inPNAS, scientists turned to chickens in their search for answers to an age old question.

It's not the questionyoure probably thinking of. The jurys still out on which came first, as well as motivations for road crossing. Instead, scientists were looking to see if certain traits commonly found in modern chickenswere the same traits selected for whenancient humans beganthe domestication process.

To study the origins of these traits, the scientists compared the DNA in modern chickens to samples obtainedfrom archeological sites ranging from 200 years BC to the 18th century.

In chickens, traits that are considered hallmarks of domestication include yellow skin. This iscommonly found in most modern breeds, and it is caused by a recessive allele inthe gene that breaks down orange-yellow compounds known as carotenoids. However, its absent in the chicken's primary ancestor, the Red Jungle Fowl, which still lives in Asia and looks a lot like a chicken. Another key trait associated with domestication is a mutation in a thyroid hormone receptorthe jungle fowl lacks it, but almost all modern chicken breeds have it.

In the past, many researchers concluded that these traits must have been selected long ago by our ancestors as they first domesticated chickens. But the in-depth genetic analysis showed that they onlybecame common in chicken breeds relatively recentlywithin the past couple hundred years.

The significance here goes far beyond chicken genetics. Its so tempting to trust neat little evolutionary storiesall the chickens have the same hormonal mutation, that must have been one of the things our ancestors selected for long, long agowhen it very well might be random chance. The genetic process of domestication cant just be assumed from modern data.

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Reading human history using ancient chicken DNA and chili peppers