1. Which came first, the chicken or the egg? That’s easy: eggs. Microfossil embryos in primitive eggs from southern China are about 600 million years old.
2. The chicken, however, now the world’s most common domestic animal, dates back a mere 4,000 or so years. Most researchers believe that Gallus gallus, the red jungle fowl, was first domesticated in East or Southeast Asia.
3. In 2014, a study ruffled feathers with claims that bones from northern China showed the wild G. gallus had been chickenized into G. gallus domesticus about 10,000 years ago.
4. But critics suggested the 2014 paper really laid an egg: The bones purported to be from chickens were, they claimed, from pheasants and possibly even dogs.
5. The word domestication is itself contentious. Some definitions focus on genetic changes due to selective breeding; others describe it as humans removing an animal from its natural environment to control its entire life cycle.
6. A 2015 study offered a broader definition: a mutually beneficial relationship, over generations, between one organism influencing reproduction and care of another.
7. The study didn’t specify humans as the domesticator because these relationships can exist beyond our sphere, such as numerous species of ants that farm fungus or herd aphids.
8. Although researchers traditionally used archaeological evidence to determine when our species domesticated another, DNA can also show when a population went from wild to mild.
9. By comparing ancient and modern DNA from a domesticated animal as well as its nearest wild relatives, researchers can identify when specific genetic mutations associated with domestication arose.
10. Some of the earliest and most common genetic markers for domestication involve changes in the endocrine system that make an animal less fearful of humans.
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