The researchers sequenced DNA from 297 rabbits in six populations in South America, Europe and Australia, all places where rabbits were introduced within the past 200 years. They compared the genetic information with the DNA of other wild and domestic rabbits.

To their surprise, the researchers discovered that all of the rabbits studied had a mixture of wild and domestic DNA.

“This was not what we had expected to find,” Leif Andersson, a professor of veterinary integrative biosciences at the Texas A&M University School of Veterinary Medicine and Biomedical Sciences and a co-author of the study, says in a news release. “We expected that feral rabbits were domestic rabbits that have somehow relearned how to live in the wild. But our findings show us that these rabbits already had a portion of wild DNA helping them survive in nature.”

The researchers found that the descendants of domestic rabbits quickly shed the docility and coat colors that humans prefer in pet bunnies, trading them for characteristics that help them thrive in the wild.

That might explain why rabbits in Australia, a continent now overrun with wild bunnies, didn’t immediately take over when domestic rabbits were first introduced. The rabbit population surged only after 1859, when the introduction of just 24 wild and domestic rabbits began a population boom that continues to this day.

Today, there are at least 150 million feral rabbits in Australia. The animals are considered invasive pests, competing with livestock and native animals, destroying native plants and crops, and even affecting groundwater absorption.