Goat genetics

Breakthrough DNA study demonstrates modern goats domesticated in Iran 10,000 years ago.

Anyone who studies ancient goat and sheep bones knows just how difficult it is to distinguish the sheep from the goats. Their bones are, at least in the early stages of domestication, almost identical. The wild ancestor was the bezoar goat, which flourishes in Iran’s Zagros Mountains. This area lies at the eastern end of the Fertile Crescent, long known to have been the cradle for goat and sheep domestication. Small bodies and short horns are clues of domestication by about 10,000 years ago in a region that has seen little archaeological research since the late 1970s.

A team of zooarchaeologists studied goat bones excavated during the 1960s and 1970s at two Zagros sites, Ganj Dareh and Tepe Abdul Hosein. Here the inhabitants had long preyed on the bezoar, focusing on large males. But then things changed, as the bones came from relatively few males, and numerous older females. This suggested that the people were managing growing herds, keeping females alive to sustain and grow the herd. Meanwhile, they culled the males for meat and by-products. Much of this was known from earlier inquiries, but today’s researchers are able to study ancient and modern goat DNA.

The new DNA analysis has revealed interbreeding among the managed goats by 8200 BC (these being the oldest livestock genomes yet sequenced). This confirms that the herders were maintaining a goat population largely separate from the region’s wild goats by this time. Although these early managed goats looked, on the outside, much more like their wild counterparts, they possessed six major mitochondrial gene sets that are identical to those present in modern domestic goat populations. Moreover, the geneticists also identified a genetic variant named STIM1-RM1 also found in other domestic animals that is known to reduce anxiety and promote learning.

Zooarchaeologist Melinda Zeder and her colleagues believe these goats therefore represent a critical moment in goat domestication, when the people were managing herds, but hadn’t yet selected for today’s commonplace external physical traits. In other words, they were experimenting with their management approaches until they succeeded in creating fully domesticated goats. The work also suggests that today’s domesticated goats are the direct descendants of those that lived in Iran, around 10,000 years ago.

Image: Bezoar ibex, Capra aegagrus aegagrus