In a long-term experiment at a Siberian fur farm, geneticists have created this new version of Vulpes vulpes, the silver fox, by allowing only the friendliest animals from each generation to breed. Having selected only the most ''tamable'' of some 45,000 foxes over 35 generations, the scientists have compressed into a mere 40 years an evolutionary process that took thousands of years to transform ancestral wolves into domestic dogs.
The original purpose of the breeding was to create a friendly breed less likely than wild animals to fight when put to death. But in time, geneticists saw that far-reaching changes they observed in the foxes' physical and neurological makeup merited scientific study. The scientists apparently underwent some changes, too. Close bonds developed between the tame foxes and their human wardens, and the staff at the fur farm is trying to find ways of saving the animals from slaughter.("Friendly" there seems like a euphemism; "gullible" or "stupid" might be more appropriate.)
The results of the experiment were domestic foxes ''as devoted as dogs but as independent as cats, capable of forming deep-rooted pair bonds with human beings'', which also developed a variety of physical differences from their wild ancestors:
The normal pattern of coat color that evolved in wild foxes as camouflage changed markedly in the genetically tamed fox population, with irregular piebald splotches of white fur appearing in some animals. The tame foxes sometimes developed floppy ears in place of the straight ones of wild foxes. The domesticated foxes generally had shorter legs and tails than ordinary foxes, and often had curly tails instead of straight, horizontal tails.
Moreover, the faces of adult tame foxes came to look more juvenile than the faces of wild adults, and many of the experimental animals developed dog-like features, Dr. Trut reported. Although no selective pressures relating to size or shape were used in breeding the animals, the skulls of tamable foxes tended to be narrower with shorter snouts than those of wild foxes.Even more interesting were neurochemical differences: the tame foxes' adrenal glands, which produce adrenaline to prepare animals for fight or flight, had declined in hormone-producing ability with each generation, while after only 12 generations, their brains contained significantly higher levels of serotonin.
Unfortunately, it appears that the project ran out of money some time in the late 1990s, and most of the foxes were destroyed or sold off to fur breeders in Scandinavia. The institute had plans to sell pups as house pets, though it is not clear whether anything came of those.
(Via a comment on this MeFi thread about the history of domestic cats.)