The domestication process has transformed the brains of foxes bred by researchers in Russia, according to new research published Monday.

Foxes bred to be tame and foxes bred for aggression both displayed increases in brain size and gray matter, researchers found in the study, published in the journal JNeurosci.

For the study, scientists took advantage of a Russian farm-fox experiment that began in 1958. Several decades ago, researchers began breeding foxes in order to better understand how wolves became dogs.

Scientists bred one fox lineage to exhibit dog-like behaviors with people. Another group of foxes was bred to react aggressively toward humans. A third group operated as a control, with those foxes not bred for any particular trait.

More than a decade ago, Erin Hecht -- who was earning her doctoral degree at the time, but is now an assistant professor of evolutionary biology at Harvard -- sent an email to the researchers working on the farm-fox experiment asking if they could collaborate on a survey of brain changes in the different lineages.

"I thought it was kind of crazy that there's this perfect opportunity to be studying how changes in brain anatomy are related to changes in the genome and changes in behavior, but nobody was really doing it yet," Hecht said in a press release.

After researchers in Russia agreed to work with her, Hecht and her colleagues collected and analyzed MRI images of the brains of several fox specimens.

The results showed the brains of both the foxes bred for tail wagging and those bred for aggression were bigger and had more gray matter than wild foxes and foxes from the control group.

Despite being bred for opposite traits, the two fox lineages featured the same enlarged brain regions: the prefrontal cortex, amygdala, hippocampus and cerebellum.

The findings suggest an animal's nervous system can be reorganized surprisingly quickly. The brain changes exhibited in the farm-fox specimens emerged after fewer than 100 generations.

Previous studies of dogs, cats, pigs, horses and other domesticated animals have shown that farm animals tend to have smaller brains their their wild ancestors.

"Both the tame and aggressive strains have been subject to intense, sustained selection on behavior, while the conventional strain undergoes no such intentional selection," researchers wrote in the paper. "Thus, it is possible that fast evolution of behavior, at least initially, may generally proceed via increases in grey matter."

The scientists suggest that future studies of the domestication process and its impact on brain size and composition can offer context for the study of human brain evolution.

"It's a more simple and straightforward way to see how evolution changes brains than we can achieve with just studying naturally occurring evolved brain changes," Hecht said.

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