I'm skeptical of this research. What if the breeder's subjective evaluation of tameness was influenced by bushy tails and floppy ears, as most people's would be? You'd end up breeding both traits in, without the same genes being involved.
"At seven or eight months, when the foxes reach sexual maturity, they are scored for tameness and assigned to one of three classes. The least domesticated foxes, those that flee from experimenters or bite when stroked or handled, are assigned to Class III. (Even Class III foxes are tamer than the calmest farm-bred foxes. Among other things, they allow themselves to be hand fed.) Foxes in Class II let themselves be petted and handled but show no emotionally friendly response to experimenters. Foxes in Class I are friendly toward experimenters, wagging their tails and whining. In the sixth generation bred for tameness we had to add an even higher-scoring category. Members of Class IE, the “domesticated elite,” are eager to establish human contact, whimpering to attract attention and sniffing and licking experimenters like dogs."
Pretty hard and fast criteria. Hard to let a slightly bushier tail affect your evaluation of whether a fox just snapped at you.
https://en.wikipedia.org/wiki/The_Mismeasure_of_Man describes research that also had hard and fast criteria, yet thumbs somehow ended up on scales anyway. The criteria you quote are a little fuzzy around the edges. "Eager to establish human contact" might well be correlated with fox cuteness.
_The Mismeasure of Man_ is biased garbage written by someone with an axe to grind who attacked strawmen and may well have made up some of his findings of 'bias' and more importantly, has completely failed to predict subsequent decades of psychological, psychiatric, and genetics results: IQ is stronger and more vindicated than ever and a major driver of molecular genetics & neuroimaging research. Try again.
How do you (unconsciously) select for attributes that do not exist? It was not until several generations that the first physiological changes began to be observed and those were in hormone levels, not morphology. In fact, the physiological, anatomical, and morphological changes were entirely unanticipated. The testing & categorization methodology is described in the article:
The tests for tameness took the following form, which was still in use as of 2009. "When a pup is one month old, an experimenter offers it food from his hand while trying to stroke and handle the pup. The pups are tested twice, once in a cage and once while moving freely with other pups in an enclosure, where they can choose to make contact either with the human experimenter or with another pup. The test is repeated monthly until the pups are six or seven months old." At the age of seven or eight months, the pups are given a tameness score and placed in one of three groups. The least domesticated are in Class III; those that allow humans to pet and handle them, but that do not respond to contact with friendliness, are in Class II; the ones that are friendly with humans are in Class I.[5] 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. They start displaying this kind of behavior before they are one month old."
