It was previously thought that modern horses were descended from a limited number of wild herds and were selectively bred, leading to the diversity in breeds that we have now. However, new DNA evidence suggests that horses have a more diverse genetic pool than once thought, according to a study published in the Proceedings of the National Academy of Sciences of the United States of America.

Based on a collaborative study between researchers at the McDonald Institute for Archaeological Research at the University of Cambridge in the United Kingdom and researchers associated with the University of Bonn in Germany, it’s now believed that at least 77 unrelated wild mares were the original breeding stock of the domesticated horse, contributing to many breeds, from the American Mustang to the Shetland pony. The study also shows that horses were domesticated in different areas of the world, according to Peter Forster, PhD, a research fellow at the University of Cambridge.

Samples of mitochondrial DNA, which is only passed along the female line, were analyzed from a total of 652 horses from different geographic locations. Researchers evaluated DNA from 25 Oriental and European breeds and the American Mustang, and they used DNA information from previously published data. The DNA samples were then compared to DNA from bones found at archaeological sites from domesticated horses which had lived in Sweden and Estonia between 1,000-2,000 years ago, samples from the Przewalski’s horse, and remains of horses frozen in the Alaskan permafrost dated between 12,000 and 28,000 years ago.

Forster said that they looked at modern living DNA and using mathematical methods, they reconstructed the family tree. “This way we can get into the past,” he said. “We can apply known mutation rates of the DNA and that can give us a time clock of how old the part of the tree we are looking at is