The Silver Fox Domestication Experiment

27 Mar

I have talked before about the origin of the domestic dog and how they resulted from the process of domestication of wolves. What i haven’t mentioned before is the silver fox domestication experiment, which really helped us to understand the whole process.


What we already knew:

Different species of domesticated animals do seem to share some common traits, changes in:

  • body size
  • fur colouration
  • timing of the reproductive cycle
  • type of hair i.e. wavy, curly, straight, fine, thick, coarse
  • ear shape
  • tail shape
  • behaviour

Darwin even recognized that drooping ears is something that never occurs in the wild, only in domesticated animals (with the exception of elephants).





Why the silver fox experiment:

Russian scientist Belyaev and other Soviet-era biolgists looked closely at the domestic dog. Whilst they knew that they were descended from wolves, they could not understand exactly what mechanism had occurred in order to result in such differences between the wolf and the domestic dog.


The hypothesis:

Belyaev came up with the hypothesis that the the anatomical and physiological changes seen in animals that are domesticated could have been the result of the selection on the basis of behavioural traits. He believed that tameness was the critical factor (how likely an animal was to interact with humans).


The study:

Belyaev and his colleagues took wild solver foxes and then bred them, with a strong selection criteria for inherent tameness. They selected for tameness and against aggression with the theory that this would result in hormonal and neurological changes which would then affect the physiology and anatomy of the animals.

Starting at one month of age, and continuing every month throughout infancy, the foxes were tested for their reactions to an experimenter. The experimenter would attempt to pet and handle the fox while offering it food. In addition, the experimenters noted whether the foxes preferred to hang out with other foxes, or with humans.

Then, upon reaching sexual maturity (seven to eight months), they had their final test and assigned an overall tameness score. They rated each fox’s tendency to approach an experimenter standing at the front of its home pen, as well as each fox’s tendency to bite the experimenters when they tried to touch it. Only those foxes that were least fearful and least aggressive were chosen for breeding. In each successive generation, less than 20 percent of individuals were allowed to breed.


The result:

The domesticated foxed were bred on the basis of single selection criteria, displayed behavioral, physiological, and anatomical characteristics that were not found in the wild population, or were found in wild foxes but with much lower frequency.

Belyaev then began breeding a line of foxes with the opposite behavioral traits, to be fearful and aggressive, using a similar method. To ensure that tameness resulted from genetic selection and not simply from experience with humans, the foxes were not trained and were only allowed short “time dosage” contact with their caretakers and experimenters.

The changes seen in the domestic foxes were much like those seen in the domestic dog compared to their ancestors, the wolf. The foxes that had been domesticated were eager to interact with humans, going as far as whimpering to attract attention, sniffing and licking their human caretakers. It was noted that they would even wag their tails when they were excited.  Their fear response was reduced and they became more willing to experience new things such as people, objects and surroundings. Their physical appearance also changed, much like the domestic dog, the foxes developed floppy ears, with tails that were short or curly. They also had changed to the colour of their fur, the shape of their skull, jaws and teeth. Like dogs, their reproductive cycles also changed.


fox proj











Further reading:





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