“There was a time when Soviet science was in a desperate state and Belyaev’s foxes were endangered,” said Ray Coppinger, a dog biologist at Hampshire College in Massachusetts who tried to obtain some of the foxes to help preserve them. But the animals seem to have left Russia only once, for Finland, in a colony that no longer survives.

There was far more to Belyaev’s experiment than the production of tame foxes. He developed a parallel colony of vicious foxes, and he started domesticating other animals, like river otters and mink. Realizing that genetics can be better studied in smaller animals, Belyaev also started a study of rats, beginning with wild rats caught locally. His rat experiment was continued after his death by Irina Plyusnina. Siberian gray rats caught in the wild, bred separately for tameness and for ferocity, have developed these entirely different behaviors in only 60 or so generations.

The collection of species bred by Belyaev and his successors form an unparalleled resource for studying the process and genetics of domestication. In a recent visit to Novosibirsk, Dr. Brian Hare of the Planck Institute used the silver foxes to probe the unusual ability of dogs to understand human gestures.

If a person hides food and then points to the location with a steady gaze, dogs will instantly pick up on the cue, while animals like chimpanzees, with considerably larger brains, will not. Dr. Hare wanted to know if dogs’ powerful rapport with humans was a quality that the original domesticators of the dog had selected for, or whether it had just come along with the tameness, as implied by Belyaev’s hypothesis.

He found that the fox kits from Belyaev’s domesticated stock did just as well as puppies in picking up cues from people about hidden food, even though they had almost no previous experience with humans. The tame kits performed much better at this task than the wild kits did. When dogs were developed from wolves, selection against fear and aggression “may have been sufficient to produce the unusual ability of dogs to use human communicative gestures,” Dr. Hare wrote last year in the journal Current Biology.

Dr. Hare believes that wolves probably have the same cognitive powers as dogs, but their ability to solve social problems, like picking up human cues to hidden food, is masked by their fear. Dogs, after their fear is removed by domestication, see humans as potential social partners, not as predators, and are ready to interact with them. But though selection for tameness was probably the first step in domesticating dogs, Dr. Hare said, they may well have adapted to human societies in other ways, with the smarter dogs leaving more progeny.