Domesticating the Silver Fox
Breeding for Tameness Changes Animals Behaviorally and Physically
Sep 11, 2008
In 1959, the Soviet Union had adopted the official science of Lysenkoism, driving the study of genetics underground. Dmitri Belyaev was a geneticist with Department of Fur Animal Breeding at the Central Research Laboratory of Fur Breeding in Moscow, but with the rise of Lysenkoism, he was fired from this position. In 1959, he took a position at the Institute for Cytology (later the Institute for Cytology and Genetics) at Novosibirsk.
The Fox Farm Experiment
In his new position, Belyaev began a new experiment. Traditional accounts of domestication suggested that humans selected animals for increased reproduction, tameness, and unusual coloration simultaneously. Belyaev thought that it was impossible for humans in the Stone Age and in the early days of agriculture to select for so many traits. He thought that it had to be a selection for tameness alone that eventually yielded all of these characteristics.
He thought that this was particularly true for dogs, which had evolved from wolves. Dogs are far less aggressive towards each other and towards their human handlers than captive imprinted wolves. However, in order to find out if selecting for tameness alone was the case for the dog, there were certain problems. Dogs and wolves interbreed, and while it is an uncommon occurrence now, it probably happened a great deal as dogs became domesticated. Wolves and dogs had “polluted” each other’s genome, so it was probably better to try another species.
Because Belyaev had experience with genetics of fur farm animals, he decided to use the silver fox in his experiments. Silver foxes are actually red foxes that have a black coat that is usually tipped with silver. This color phase occurs in North America in the wild, but in captivity it has been reproduced as a specific fur variety.
Selection Criteria
Belyaev’s team selected foxes for their breeding program on whether the animals exhibited the lowest amounts of fear and avoidance behavior before humans. 130 foxes were chosen from many different fur farms throughout the Soviet Union. These foxes were then bred to each other. Although these foxes had been bred for many generations in captivity, they were not tame animals. The foxes still had the behavior of a wild fox, which seeks to avoid humans at all costs. Most of these foxes on fur farms exhibited a great deal of fear of humans. These 130 were just slightly less likely to run from humans than the typical silver fox population.
Only the tamest animals from each generation were allowed to breed. Inbreeding was intentionally kept at a minimum within the population, just to make sure that it was selection for tameness alone that was being tested. By the tenth generation, nearly twenty percent of all foxes were friendly and quite tame.
As the experiment continued, something else began to happen. By generations eight and ten, the foxes started developing spots. Some of them were even marked like border collies. Some foxes developed shorter legs and tails than the wild type, while others had tails that curled over their backs. Even more unusually, a few vixens had estrus cycles longer than normal, and a few also had estrus cycles twice a year. All of these traits are traits of domestic animals.
Selection of Tameness Alone Yielded These Changes
Belyaev’s hypothesis was supported in this experiment that selection for tameness alone led to the unusual coloration and coats in domestic animals as well as their increased reproduction. Although genetics was not an accepted science in the Soviet Union in the 1950s, Belyaev’s experiment showed that genetic selection for tameness could also select for other genes as well. It also showed that domestication could be a rather quick process, and that Stone Age people could have potentially created genetically tame wolves within a the truncated lifespan of a person of that time. These findings greatly shape how we understand the domestication process.
Sources:
Paper by Lyudmila Trut, who worked with Belyaev
Cornell University's page on the history of the fox farm experiment
