An interdisciplinary study has determined that modern chickens only developed several of their most prized domestic traits within the last 1,000 years. A British team made up of archaeologists, geneticists, statisticians, and historians made the discovery by sequencing ancient DNA from chicken bone samples collected at archaeological sites across Europe, whose dates range from Roman times through the postmedieval period, and creating a model that pinpoints when specific chicken genes began to change. Though humans first domesticated jungle fowl in Asia around 6,000 years ago, it was only in the High Middle Ages that chickens began to consistently display both a lack of aggression and the capacity to lay eggs more regularly. According to Liisa Loog of the University of Oxford, a lead author of the study, one individual genetic variant may be responsible. “This particular mutation we’re looking at has been shown in modern chickens to both make them friendlier and enable them to lay eggs earlier on in the breeding season,” she says.
Humans, of course, favored these cooperative chickens and, unwittingly, exerted selective pressure that perpetuated their genes. To understand why chickens evolved so rapidly, Loog and her colleagues point to the spread of Christianity throughout Europe a thousand years ago, when dogmatic prohibitions on the consumption of four-legged animals and fasting rituals may have increased the demand for poultry. “Every time we see a transformation like this we just assume that it must have taken a very long time to happen,” says Loog. Instead, it seems that a widespread and rapid shift in the dietary behavior of large populations accelerated the kind of evolutionary change in chickens that is often imagined to occur over millennia. Loog explains, “It kind of shows you don’t really need to know much about genetics to make genetically modified organisms.”
