Evolution and Aggressive Behavior: the Russian Silver Fox Domestication and How it Might Benefit Studies into Human Behavioral Disorders

2009-08-24

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Domestication of Animals

Domestication of the Russian Silver Fox is an experiment in evolution that was first undertaken by the Soviet scientist Dmitri Belyaev in 1959. Formerly the Head of the Department of Fur Animal Breeding at the Central Research Laboratory of Fur Breeding in Moscow, Belyaev was relieved of his post in 1948; his belief in Mendelian genetics clashed with the Soviet State sponsored Lysenkoism genetics. In 1958, he went to Siberia as the Director of the Institute of Cytology and Genetics of the Siberian Department of the Russian Academy of Science in Novosibirsk, and it was here that he began his domestication experiments; explaining these as a study of animal physiology, he was able to carry out his research without governmental interference.

After his death in 1985, he was succeeded by Dr. Lyudmila N. Trut. The experiment and its results become known internationally only in 1999 when Dr. Trut published a paper in the journal American Scientist.

The Russian Silver Fox Domestication Experiment

For his research, Belyaev selected the Russian Silver Fox since it is related to dogs. Obtaining 130 animals - 30 males and 100 females - from an Estonian commercial fur farm, he tested them for tame and aggressive behaviors. His theory was that the tameness factor, rather than other factors like size or reproduction, played a crucial role in the process of domestication.

He selected and bred successive generations of tame foxes, taking care to avoid inbreeding. Similarly, he also bred a line of aggressive foxes. After eight generations the tame foxes began to display distinct behavioral and physical changes from both their farm bred aggressive counterparts and wild silver foxes. Over 35 generations of tame foxes, numbering over 45000, were bred in a period of 40 years, and the researchers kept human contact to a minimum and did not train the foxes in any way.

Research Observations

The silver foxes began to show tame, doglike behaviours like whining to get attention, licking, tail-wagging and barking.
They began to display floppy ears, shorter legs, shorter and curled tails and spotted fur.
They began to show narrower skulls and shorter snouts than that of wild foxes.
Females began to come into heat twice a year instead of just once as in the case of wild foxes.
Tame fox puppies opened their eyes sooner and developed a fear response later than wild fox puppies.

The researchers also noted decreased adrenal hormone production and increased serotonin levels in the tame foxes. The former was linked with an animal’s fear and aggression factors and the latter affected it on the psychological level. The balance between the two caused an animal to behave in a particular way and changing that balance brought about genetic changes that influenced both the animal’s behavioral pattern and its developmental process. Not always a good thing, according to Dr. Trut; docility might make the foxes excellent house pets, but wouldn’t win them any favors in the wild.

Later experiments crossbred tame foxes with the aggressive ones and then bred the offspring back with tame foxes. Researchers found a genetic basis for the behavioral changes. They observed 40 gene differences between tame farm-bred silver foxes and aggressive farm-bred silver foxes, and 2700 gene difference between the two sets of farm-bred silver foxes and wild silver foxes. A paper on this was published in the 22 November 2005 issue of Current Biology.

In the long run, researchers hope to identify the genes that cause tame and aggressive behaviors in the foxes, and, by understanding these, they hope understand and find a genetic cure for autism and other behavior impaired disorders in humans.