Why does a wild rabbit flee when a person approaches it, but a domestic rabbit sticks around for a treat? A new study finds that domestication may have triggered changes in the brains of these—and perhaps other—animals that have helped them adapt to their new, human-dominated environment.
The new study provides “specific and new insights” into the ongoing debate over the physiological factors shaping domestication and evolution, says Marcelo Sánchez-Villagra, a professor of paleobiology at the University of Zurich in Switzerland who was not involved with the work.
The leader of the research team, animal geneticist Leif Andersson of Uppsala University in Sweden and Texas A&M University in College Station, thinks the process of domestication has led to changes in brain structure that allow the rabbit to be less nervous around humans. To find out, he and colleagues took MRI scans of the brains of eight wild and eight domestic rabbits and compared the results.
The team found that the amygdala, a region of the brain that processes fear and anxiety, is 10% smaller in domesticated rabbits than in wild rabbits. Meanwhile, the medial prefrontal cortex, which controls responses to aggressive behavior and fear, is 11% larger in domesticated rabbits. The researchers also found that the brains of domesticated rabbits are less able to process information related to fight-or-flight responses because they have less white matter than their feral cousins do. White matter helps connect nerve cells through signal-transferring fibers called axons and can influence the brain's information processing. When a wild rabbit is in danger, more white matter is needed for faster reflexes and for learning what to be afraid of.
These changes in the brain reduce emotions like fear and aggression, creating the docile personalities found in domesticated rabbit, the researchers conclude today in the Proceedings of the National Academy of Sciences.
Changes in brain shape occurred in domesticated animals because they do not face the same pressures as their wild counterparts do, Andersson says. When we breed domesticated rabbits, we select for tameness, which in turn selects genes that affect the brain’s structure, he says. “Behaviors related to fear and aggression are needed for survival. But the domesticated rabbit does not face the same pressures. It has evolved to live in a human-dominated environment, where food and shelter is readily available and provided for them.”
Any study that compares wild and domesticated animals suffers from the fact that the first wild and domesticated populations are no longer around, Sánchez-Villagra notes. But he says that what Andersson’s team did is “a good approximation of what occurred when the first domestication happened and is an important subject in evolutionary studies.”
*Correction, 26 June, 12:35 p.m.: The caption for the amygdala art has been changed because the previous caption misstated a difference between wild and domestic rabbits.