Tame Silver Foxes are the results of nearly 50 years of experiments in Russia to domesticate the Silver Fox. Notably, the foxes did not only become more tame, but more dog-like as well: the new foxes lost their distinctive musky “fox smell”, became more friendly with humans, put their ears down (like dogs), wagged their tails when happy and began to vocalize and bark like domesticated dogs. The breeding project was set up by Russian scientist Dmitri Belyaev, encouraged by the Communist Party of the time because of its link with the aim to control and improve the human condition.
Scientists were interested by the topic of domestication, and how wolves were able to become tame, like dogs. They saw some retention of juvenile traits by adult dogs: both morphological ones such as skulls that were unusually broad for their length, and behavioural ones such as whining, barking and submissiveness.
Belyaev believed that the key factor selected for domestication of dogs was not size or reproduction, but behaviour; specifically amenability to domestication, or tamability. More than any other quality, Belyaev believed, tamability must have determined how well an animal would adapt to life among human beings. Because behavior is rooted in biology, selecting for tameness and against aggression means selecting for physiological changes in the systems that govern the body’s hormones and neurochemicals.
Belyaev decided to test his theory by domesticating foxes; in particular the Russian Silver Fox. He placed a population of them in the same process of domestication, and he decided to submit this population to a strong selection pressure for inherent tameness.
The result is that Russian scientists now have a number of tame foxes which are fundamentally different in temperament and behaviour from their wild forebears. Some important changes in physiology and morphology are now visible, such as mottled or spotted colored fur.
Physically, the foxes differ markedly from their wild relatives. Some of the differences have obvious links to the changes in their social behavior. In dogs, for example, it is well known that the first weeks of life are crucial for forming primary social bonds with human beings. The “window” of bonding opens when a puppy becomes able to sense and explore its surroundings, and it closes when the pup starts to fear unknown stimuli.
According to our studies, nondomesticated fox pups start responding to auditory stimuli on day 16 after birth, and their eyes are completely open by day 18 or 19. On average, our domesticated fox pups respond to sounds two days earlier and open their eyes a day earlier than their nondomesticated cousins. Nondomesticated foxes first show the fear response at 6 weeks of age; domesticated ones show it after 9 weeks or even later. (Dogs show it at 8 to 12 weeks, depending on the breed.) As a result, domesticated pups have more time to become incorporated into a human social environment.
Moreover, we have found that the delayed development of the fear response is linked to changes in plasma levels of corticosteroids, hormones concerned with an animal’s adaptation to stress. In foxes, the level of corticosteroids rises sharply between the ages of 2 to 4 months and reach adult levels by the age of 8 months. One of our studies found that the more advanced an animal’s selection for domesticated behavior was, the later it showed the fear response and the later came the surge in its plasma corticosteroids. Thus, selection for domestication gives rises to changes in the timing of the postnatal development of certain physiological and hormonal mechanisms underlying the formation of social behavior.
Other physical changes mirror those in dogs and other domesticated animals. In our foxes, novel traits began to appear in the eighth to tenth selected generations. The first ones we noted were changes in the foxes’ coat color, chiefly a loss of pigment in certain areas of the body, leading in some cases to a star-shaped pattern on the face similar to that seen in some breeds of dog. Next came traits such as floppy ears and rolled tails similar to those in some breeds of dog. After 15 to 20 generations we noted the appearance of foxes with shorter tails and legs and with underbites or overbites. The novel traits are still fairly rare. Most of them show up in no more than a few animals per 100 to a few per 10,000. Some have been seen in commercial populations, though at levels at least a magnitude lower than we recorded in our domesticated foxes.
Read : Belyaevs’s Hypothesis on tame silver fox.