Back in 1959, Russian geneticist Dmitry Belyaev began an incredible experiment to study the process of domestication, using the silver fox as his subject. He noticed similar patterns of physical traits among domesticated animals – such as the aforementioned floppy ears and curly tails – and hypothesized that by selecting and breeding foxes only for tameness, he believed these traits would arise too in foxes. Starting with a population of ranched foxes from fur farms, Belyaev bred only the tamest animals, gauging them based on their reactions to and interactions with human handlers. His results were astounding – by the 6th generation of breeding, a portion of the fox pups were competing with each other, vying for the attention of their handlers much like dogs.
Dmitry Belyaev and his foxes. (Source)
By the 8th generation onwards, physical traits found in other domestic species began to appear, such as the floppy ears, curly tails, pie-baldness, and shorter legs and tails. Belyaev continued his domestication experiment until his death in 1985, and it is carried on today by the researchers who had worked under him. Continuing his work, by 1999 70-80% of the fox pups fell under the highest category of tameness, eager for human attention even before one month of age. Through many generations of careful selection and breeding, Belyaev’s research produced a unique population of foxes that were undeniably domestic (Trut, 1999).