What did the silver-fox experiment reveal about taming?

It revealed that selecting animals only for friendliness can change much more than their temper. In Novosibirsk, Russia, the biologist Dmitry Belyayev wanted to test how dogs could have come from wolves. His idea was that early humans had selected for one thing alone, tameness, and that the rest followed. So in 1952 Lyudmila Trut, the programme's manager, started collecting the tamest foxes from fur farms, and in each generation only the tamest were allowed to breed.

The foxes were never trained, so any change would come from genes and not from upbringing. When a cub was a month old it was tested: someone offered it food and tried to stroke it, and in an enclosure the cub could choose between a person and other cubs. The first physiological change was a lower level of adrenaline. After eight to ten generations, the tame foxes began to show multi-coloured coats, and then floppy ears and rolled tails like those of some dog breeds. By 1999, after 40 years and 45,000 foxes, Trut reported animals as tame and as eager to please as a dog.

The foxes also surprised researchers. Brian Hare found that the tame fox kits did as well as puppies at picking up human cues about hidden food, even though they had almost no experience with humans. They had been bred for being nice, not for being smart.

Belyayev's idea is known as domestication syndrome, the shared set of traits that domesticated animals tend to show. It is still debated. In 2019 critics argued that the syndrome may not exist, and that the foxes were not totally wild to begin with. Other scientists answered that the foxes gained new traits only after the experiment began.