Fox breeding experiments reveal brain changes linked to domestication

Researchers at Cornell University identified fewer neurons in a specific brain region of tame foxes compared to aggressive foxes.

This discovery helps explain how wild animals like wolves transformed into domestic dogs over thousands of years. The study builds on a long-running experiment started in 1959 by Soviet geneticist Dmitry Belyaev and Lyudmila Trut in Siberia. They bred silver foxes from fur farms, selecting only those that showed the least fear or aggression toward humans.

Within six generations, the foxes began seeking human contact and developed physical traits like floppy ears and shorter snouts. By 1970, the researchers also bred a separate group of foxes specifically for hostile behavior to create two contrasting populations. Eirene Markenscoff-Papadimitriou and her team at Cornell University examined nine preserved fox brains to study the ventromedial hypothalamus, a region involved in social behavior and aggression.

Using fluorescent probes, the scientists found that the tame foxes had fewer neurons associated with aggression than the hostile foxes. While the small sample size means researchers cannot yet prove these differences cause tameness, the results suggest that selective breeding can physically reshape the cellular makeup of the brain. These findings align with a separate study published in Molecular Biology and Evolution that analyzed genetic datasets from 2,709 dogs.

That research showed that selection for reduced fear and aggression is more consistent across dog lineages than selection for physical traits. Together, these studies suggest that biological changes to fear and social behavior systems were likely some of the earliest steps in the domestication of wolves.