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Goats are one tough breed, surviving Atlantic Ocean crossings with Christopher Columbus and the Mayflower’s pilgrims—and tolerating everyday perils from drought to parasites. Now, research has uncovered the origins of their hardiness: Some ancient hanky panky with a wild goat cousin gave the domesticated species (Capra aegagrus hircus) a gene that protects against parasitic worm infections. That gene joined others to help make goats among the first animals to be domesticated.

The finding underscores the importance of interbreeding with wild populations in the early days of domestication, says Melinda Zeder, an emeritus anthropological archaeologist at the Smithsonian Institution’s National Museum of Natural History, who was not involved with the work. “It gives us a lesson about how domesticated crops and livestock were able to disperse as widely as they did.”

Many researchers consider goats to be the first animals domesticated—11,000 years ago in the ancient Fertile Crescent. Today, they supply more of the world’s milk than all the dairy cows combined. Researchers know humans first corralled the domestic goat’s wild ancestor, most likely a bezoar (C. aegagrus) in both Turkey and Iran, but exactly what transpired between then and now has been a mystery.

Jiang Yu, an animal geneticist at Northwest A&F University, and an international team sequenced the genomes of 88 domestic goats from around the world, six wild goat species, and four goat fossils. They compared their data with previously gathered genomic information about 131 other domesticated, wild, and ancient goats to determine which parts of the goat genome were important to domestication.

One gene, MUC6, seemed particularly important. Today, almost every domestic goat has a version of the MUC6 gene that came from a wild goat called the West Caucasian tur, Jiang and colleagues report today in Science Advances. Working backward, the team calculated that the tur version of this MUC6 gene entered the goat genome 7200 years ago, likely through interbreeding.

The MUC6 gene codes for a protein found in the lining of the gut. In other animals, it is part of the immune defense system. To see whether it could protect against parasites, the researchers checked the stools of goats carrying either the tur version of MUC6 or another version found in a few domestic goats for nematode worm eggs. There were far fewer eggs in the stool of the goats with the tur version, suggesting that version is protective, the researchers report.

It makes sense that the tur version of this gene would better fight parasites, Jiang says. The tur lives near the coast of the Black Sea, where the warm, wet climate likely fostered more pathogens than goats’ original home in the drier regions of southwest Asia.

Some researchers think the most important traits for domestication have to do with physical appearance or economically valuable qualities such as milk production. But this study suggests breeding livestock that could survive in crowded conditions—where diseases are more likely—was more critical in the early years, Jiang says. Because of the advantage provided by the tur version of MUC6, it spread to 60% of the domesticated goats within 1000 years—a speed of spread that previously had been “unimaginable,” Jiang notes. “It proved the extreme desire of people to acquire healthy animals.”

In addition to MUC6, the team found other genes in domestic goats that came from other wild goats about the same time 7200 years ago. These genes—possibly linked to behavior—may have made the goats more docile, Jiang says. But the researchers need to test that idea.

The paper shows domestication was a dynamic process with genes from other species being gained and lost through the millennia, Zeder says. “It’s not a ‘one and done,’” she explains. “The ability to have the uptake of new genes better enabled them to adapt.”