Goat busters track domestication - physiologic changes and evolution of goats into a domesticated animal - Brief Article

Science News, April 8, 2000

People began to domesticate wild goats at least 10,000 years ago in the Zagros Mountains of western Iran, according to a new study. It indicates that at that time, villagers in the area experimented with ways of controlling herds. These early domesticators primarily slaughtered male goats that had not reached their reproductive prime, leaving mature males to breed with a herd's adult females, say the researchers.

Goats in these early managed herds probably looked much like wild goats, both physically and genetically, say Melinda A. Zeder of the Smithsonian Institution's National Museum of Natural History in Washington, D.C., and Brian Hesse of the University of Alabama at Birmingham. Over time, isolation of managed herds and the introduction of selective breeding produced changes in domesticated goats, the two anthropologists propose.

Some researchers have argued that declines in overall body size of goat skeletons unearthed at two ancient village sites in the Zagros Mountains reflect early domestication. However, goats from these sites, Ganj Dareh and Ali Kosh, fall within the size range of a sample of modern wild-goat skeletons, Zeder found in a preliminary study.

The Ganj Dareh and Ali Kosh samples contain a large proportion of bones from young males, the scientists report in the March 24 SCIENCE. Previous investigators at the sites had excluded these bones--which had not developed fully but still were larger than comparable bones of fully grown females--from body-size estimates for adult goats. Because more females than males reached maturity, these calculations mistakenly portrayed the villagers' animals as much smaller than wild goats, Zeder and Hesse assert.

Evidence that people had primarily killed young male goats came as no surprise to Hesse. He had previously theorized that early herders mainly killed young males for meat and kept most females and a few older males as breeding stock. In contrast, hunters interested in a quicker return on their effort often targeted the largest males in a herd or killed many animals at once, Hesse had proposed.

The researchers determined that Ganj Dareh was inhabited about 10,000 years ago, for a span of no more than 100 to 200 years. Settlement of Ali Kosh occurred 500 to 1,000 years later and lasted about 500 years. Radiocarbon analyses generated age estimates from tiny fragments of bone and charred seeds found in a range of soil layers at both sites.

Emergence of a warmer, wetter climate in western Asia 15,000 years ago instigated a spread of grasslands and a resurgence of animals such as sheep, goats, and pigs, Zeder holds. Soon, people there took the first steps toward domestication by searching for ways to manage animal herds, in her view.