Domesticated silver fox
[2][3] In 2019, an international research team questioned the conclusion that this experiment had provided strong support for the validity of domestication syndrome.
Like other scientists, he "could not figure out what mechanism could account for the differences in anatomy, physiology, and behavior" that were obvious in dogs, but he was confident that the answer lay "in the principles of Mendelian inheritance.
"[7] Belyayev further theorized that this attribute "had dragged along with it most of the other features that distinguish domestic animals from their wild forebears, like droopy ears, patches of white in the fur and changes in skull shape.
"[8] Jason Goldman of Scientific American said, "Belyaev hypothesized that the anatomical and physiological changes seen in domesticated animals could have been the result of selection on the basis of behavioral traits.
"[6] Academic Claudio J. Bidau wrote that Belyayev's suspicion was "that domestication was ruled by a process of 'destabilizing selection' affecting mechanisms of ontogenetic neuroendocrine control, either directly or indirectly in response to the appearance of a factor of stress", and that "the key factor of domestication producing striking similar results in many species is selection for tameness.
"[9] Goldman said Belyayev wondered if a breeding program that involved "selecting for tameness and against aggression would result in hormonal and neurochemical changes, since behavior ultimately emerged from biology.
It could be that the anatomical differences in domesticated dogs were related to the genetic changes underlying the behavioral temperament for which they selected (tameness and low aggression).
Belyayev designed a selective-breeding program for the foxes that was intended to reproduce a single major factor, namely "a strong selection pressure for tamability".
After only six generations, Belyayev and his team had to add a higher category, Class IE, the "domesticated elite", which "are eager to establish human contact, whimpering to attract attention and sniffing and licking experimenters like dogs.
Belyayev and his team "theorized that adrenaline might share a biochemical pathway with melanin, which controls pigment production in fur", a hypothesis that has since been confirmed by research.
The experimenters also discovered that the domesticated foxes show a "fear response" several weeks later than their wild counterparts, and that this delay is "linked to changes in plasma levels of corticosteroids, hormones concerned with an animal's adaptation to stress".
"[2] Trut wrote in 1999 "that after 40 years of the experiment, and the breeding of 45,000 foxes, a group of animals had emerged that were as tame and as eager to please as a dog."
[13] So it was, in the words of Scientific American, that Belyayev's experimental animals and their descendants have been said to "form an unparalleled resource for studying the process and genetics of domestication".
[8] Brian Hare, a biological anthropologist, wanted to study "the unusual ability of dogs to understand human gestures".
[16][17][3] When Anna Kukekova, a Russian-born postdoctoral researcher in molecular genetics at Cornell University, read about the project's financial difficulties, she secured funding from the National Institutes of Health and joined in Trut's effort to complete Belyayev's work, making it a joint Russian-American initiative.
[14][18][19] The results from the experiments led the scientists at the institute to research domestication of other animals, such as rats in 1972, mink, and river otters.
For example, the "star-shaped" pattern was found to be controlled by one dominant gene that was incompletely penetrant, "but its penetrance is significantly higher in offspring from tame mothers than from aggressive ones..."[22] Trut reported that female foxes heterozygous for the gene controlling the star pattern also influenced the number of male pups, increasing the number of males over the expected 50%.
As the fox experiment has progressed over time, it was found that in general the number of male pups increased over the expected 50% to approximately 54%.
Belyaev stated: "Perhaps the most important observation emerging from this series of experiments is the fact that tame females exhibit statistically significant changes in certain neurochemical characteristics in such regions of the brain as the hypothalamus, midbrain, and hippocampus.
In order to help understand the neurobiology of behavior, fox and dog orthologs of serotonin receptor genes were cloned.
[27] In 2005, DNA microarrays were utilized to find the differences in genetic expression between domesticated, non-domesticated (farm-raised), and wild foxes.
He and his team started working with rats in 1972, and later with minks and, briefly, with river otters, although this last experiment was abandoned because the species "proved difficult to breed".
"Siberian gray rats caught in the wild, bred separately for tameness and for ferocity", reported The New York Times, "have developed ... entirely different behaviors in only 60 or so generations".
"[15] In 2006, Frank Albert, a graduate student at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, was helping to continue Belyayev's work by studying the genetic roots of the differences between the tame and hyper-aggressive rats.
[8] In 2009, Albert and several colleagues published a paper in Genetics[30] about the results of their cross-breeding of tame and hyper-aggressive rats, a stock of which they had established in Leipzig.
[30] In 2011, it was reported that Albert's team had "found several key regions of the genome that have a strong effect on tameness" and that they suspected the involvement of "at least half a dozen genes".
Raymond Coppinger, a dog biologist at Hampshire College in Massachusetts, noted that at one time "Soviet science was in a desperate state and Belyayev's foxes were endangered", but his own efforts "to obtain some of the foxes to help preserve them" had been unsuccessful, with the animals apparently having "left Russia only once, for Finland, in a colony that no longer survives".
[8] The author of the National Geographic article about the experiments, however, said that his translator, Luda Mekertycheva, had adopted two foxes from Novosibirsk and that they had proven to be wonderful companions who "jump on my back when I kneel to give them food, sit when I pet them, and take vitamins from my hand".
[36][37] As of 2023, 12 sterilized foxes have been exported from the Institute of Cytology and Genetics to the Judith A. Bassett Canid Education and Conservation Center in Santa Ysabel, California.
Conversely, Adam Wilkins of Humboldt University of Berlin, challenges Karlsson's criticisms, analyzing how subtle developmental causes can produce an array of diverse and non-uniform "domestication syndrome" effects in different species.
