Ancient hunters and farmers living in the foothills and valleys of western Iran’s verdant highlands may have been among the first people to domesticate livestock. Now, a new study—which includes the oldest livestock genome yet sequenced—bolsters that notion, appearing to capture genetic and archaeological evidence of a transitional stage between wild-hunted goats and their domesticated descendants.
The study has captured “the ’ground zero’ for goat domestication, or close to it,” says David MacHugh, an animal geneticist at University College Dublin. And because the advent of livestock domestication helped pave the way for larger populations and complex societies, he says, “it is really one of the pivotal moments in prehistory.”
Since the 1950s, archaeologists have unearthed ancient livestock bones near Iran’s Zagros Mountains. The area lies at the eastern end of the Fertile Crescent, the region considered the cradle of agriculture and several early civilizations. Animal remains—some of which date to about 10,000 years ago—show signs of domestication, such as smaller bodies and shorter horns. Evidence of early pig and sheep domestication has been found in the region, as well.
Much of the archaeological research in the area halted because of the Iranian Revolution in the late 1970s, and the Iran-Iraq War, which began in 1980. “This region sort of fell into a dark abyss for quite a while,” says Melinda Zeder, an emeritus archaeologist at the Smithsonian Institution’s National Museum of Natural History. “It’s now seeing a recent resurgence of interest in all sorts of domestication issues, with goats being a primary one.”
To learn about the process of early animal domestication, Zeder and others—including several Iranian archaeologists—analyzed goat bones excavated in the 1960s and ’70s from two sites in the Zagros Mountains, Ganj Dareh and Tepe Abdul Hosein. People lived, hunted, and grew crops in these fertile valleys from about 8200 to 7600 B.C.E. The wild ancestor of today’s domestic goat (Capra aegagrus hircus), the bezoar (C. aegagrus), was their primary prey.
The pattern of male and female goat remains at these sites was the first clue that people were likely managing herds, not just hunting them. “Hunters and herders target different kinds of animals,” Zeder explains. “Hunters are after the ‘bang for your buck’ fast return, so they go for big adults.” Herders, meanwhile, care less about individual size, focusing instead on keeping females alive to sustain and grow the herd, she says. As a result, herders tend to cull most young males and keep lots of older females.
That’s exactly the pattern the researchers saw at Ganj Dareh and Tepe Abdul Hosein: relatively few males and lots of older females. Hoof impressions imprinted in mud bricks at Ganj Dareh further strengthened the case that people here were managing goats, as wild goats probably weren’t tromping through the village. Strangely, though, these seemingly herded goats looked exactly like wild bezoars, with large bodies and horns. So, the researchers turned to ancient DNA.
Comparing the ancient goat DNA with that of modern wild goats from the region, the scientists found distinct genetic clusters indicating the apparently managed goats were being bred with one another, they report today in the Proceedings of the National Academy of Sciences. This confirms the herders maintained a goat population largely separate from the region’s wild goats, Zeder says. The earliest of the goat remains date to about 8200 B.C.E., making the DNA in the study the oldest livestock genomes yet sequenced.
Within these early managed goats, the researchers identified the six major mitochondrial haplotypes, or sets of genes inherited along the female line, that are present in modern domestic goat populations. That find suggests today’s goats are direct descendants of those that lived 10,000 years ago, Zeder says. Within the genomes of these ancient goats, the researchers also identified a genetic variant called STIM1-RRM1 that is known in other domestic animals to help reduce anxiety and promote learning.
The upshot, Zeder says, is that these ancient goats appear to represent a critical moment in domestication in which people were managing herds but hadn’t yet selected for the physical traits that you’d recognize at the petting zoo.
“This is a fascinating study,” says Cheryl Makarewicz, an archaeozoologist at the University of Kiel who wasn’t involved with the work. The results suggest the earliest livestock herders tinkered with management strategies before they succeeded in domesticating their animals, she adds. “There was a lot of experimentation going on.”