Genetics was an outlaw science in the early Soviet Union: the idea that characteristics are inheritable smacked of an elitist plot to claim the class system was biologically predetermined.
Biologist Dmitri Belyaev (1917-1985) was dismissed from his post in a Moscow fur breeding laboratory in 1948 for his insistence that Darwinian artificial selection could produce rapid evolutionary change. During the Khrushchev ideological thaw, he was appointed head of a genetics institute in southern Siberia, safely away from the establishment.
From 1959 until his death, he was responsible for a spectacular experiment. Silver foxes were highly prized for their pelts, but they did not fare well in captivity. The obvious solution: breed them for docility. Belyaev patiently selected the foxes that were the least agitated around humans, and after only 40 generations had basically recapitulated the domestication of the wolf into the dog.
The Wild foxes had pointed ears, strong jaws, long tails, and silver coats.
The domesticated foxes had floppy ears, overbites, short tails which they wagged — and, ironically, piebald coats which were basically useless to furriers!
These are all characteristics which, along with playfulness and trust of humans, they share with infant feral foxes. The wild ones grow out of these traits, but the domesticated ones were bred to retain them. (Evolutionary change to retain childlike characteristics is called neoteny, and it’s an important part of hominid evolution: humans look much more like baby apes and chimpanzees than we do the adult primates.)
There’s a sad coda to this tale: the breeding was continued after Belyaev’s death, and is still ongoing, but the domesticated fox population is severely reduced due to post-Soviet economic troubles; many of them were sold as pets.
Belyaev, D. K., Ruvinsky, A.o., Trut, L.N. 1981. Inherited activation-inactivation of the star gene in foxes. The Journal of Heredity 72:264–274.
Trut, L.N. 1999) Early Canid Domestication: The Farm-Fox Experiment. American Scientist 87(2): 160
If you want to read more, here is a great article written by the scientist who inherited the experiment from Belyaev.