Karen Pence, next to Vice President Pence, holds the family's pet rabbit, Marlon Bundo, while speaking at an event in May. (Mandel Ngan/AFP/Getty Images)

The story of how rabbits supposedly became domesticated animals is a strange one. Around the year 600, the tale goes, Pope Gregory the Great issued a papal edict declaring that fetal rabbits were not meat. Because fluid-filled amniotic sacs surrounded rabbit fetuses, they counted as fish. Eaten this way the rabbits were a delicacy — a snack called laurices (always plural because, like potato chips, you wouldn't eat just one). French Catholic monks, who abstained from meat while observing Lent, pounced on the opportunity. Monks began to breed the animals like, well, rabbits. Skittish wild animals went into the monastery. After a few generations, out came tame and fluffy pets.

This just-so story was plausible enough that the scientific community swallowed it. The location made sense: Wild European rabbits from the Iberian peninsula and France are the closest genetic relatives to pet rabbits. Greger Larson, a biologist at the University of Oxford who studies domestication, recalled hearing about Pope Gregory at a conference a few years ago. The rabbit genome had just been sequenced.

The problem, as Larson and his colleagues discovered, is the story isn't true. “It turned out that the whole thing was a house of cards,” he said.

Larson did not set out to debunk a legend. In fact, his initial goal was to find proof of the date. Researchers like Larson use rates of mutation, in a method called a molecular clock, to estimate the age of domesticated species. But this method comes with baked-in ambiguities. If rabbits had a known domestication date, Larson could use the timeline to improve these molecular methods, like setting a watch to an atomic clock. He asked archaeologist and computer scientist Evan Irving-Pease, then working on a master's thesis, to hunt down a copy of the papal document or any supporting information.

Irving-Pease began to unwind knotty citations and references until he reached the end of the thread: Pope Gregory never issued such an edict. Laurices didn't appear to be popular during Lent. Instead, Irving-Pease, Larson and their colleagues mapped out a much more complex picture of rabbit domestication, which the journal Trends in Ecology & Evolution published on Wednesday.

“This is a timely paper that brings a healthy dose of skepticism regarding the timing of rabbit domestication and the associated cultural context,” said Miguel Carneiro of the University of Porto in Portugal, who has studied rabbit domestication and was not involved with this project.

Because of the latest research, there no longer is a black line in the historical record that divides wild rabbits from pet bunnies. “It’s a great story for us, because it jarred us out of our assumptions and drove us in a new direction,” Larson said.

Archaeological evidence from about 20,000 years ago in southwest Europe indicates that the first interaction between humans and rabbits was that of hunter and food. “If there's a protein source, you’ll go and exploit it,” Larson said. “Lots of people were eating rabbit.”

Not until the Middle Ages did people begin to transport rabbits across Europe, Larson and his colleagues reported. People built artificial warrens called pillow mounds in Britain, raised off the ground because the rabbits would have struggled to burrow into the tough English soil. Along the way, they became much calmer.

“Although pet rabbits are closely genetically related to French wild rabbits, selection has been intense, and they differ in numerous traits, of which behavior is the most striking,” Carneiro said. “Pet rabbits are tame and tolerate well human presence while wild rabbits are extremely fearful and have a very strong flight response.”

Skeletal differences appeared in the 18th century, when people began to keep and breed rabbits as pets. Physical changes have only accelerated since then, with dozens of colorful rabbit breeds. The smallest are called “teacup rabbits”; others are giants weighing 40 pounds or more.

An analysis of wild rabbit fossils indicates a genetic divergence 15,000 years ago, the study authors said. In Larson's view, this represents a split in wild populations, as Ice Age glaciers moved, and does not show effects of domestication.

Carneiro is hesitant to make conclusions from the rabbit genetics, citing the wide uncertainty in reported rabbit mutation rates and the limited data set in the new report. If rabbits mutated slowly, like humans, the divergence “would be an order of magnitude lower,” he said. “If they assumed a similar estimate to that in mice, divergence times would be on the order of 50,000 years.”

The interpretation of historical records in the new paper was “excellent,” Carneiro said. But he sees an important distinction between rabbits and other animals. “Rabbit domestication was likely a more direct process when compared to other species, such as dog, pigs, and chicken, which were geographically widespread,” he said. By the time rabbits were housed in hutches, humans already had “a 10,000-year history of keeping domestic animals.”

Larson says that past knowledge of animal husbandry does not easily translate to domesticating new ones. Even the most recent cases have been accidents, he said: The first hamsters housed in captivity, a very recent addition to the pet pantheon, were not meant to be pets — they were captured from Syria in the 1930s to be medical subjects.

So when exactly over the last 20,000 years were the rabbits domesticated? Ultimately, rabbit domestication was not a moment in time but a continuum, Larson has concluded. At the very least, it's safe to say that hungry monks were not responsible.

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