The marble fox or "Canadian marble fox" is the social media nickname for domesticated red foxes bred at the Institute of Cytology and Genetics at Novosibirsk, Russia, begun as an experiment by Dmitry Belyayev in 1959 to explore how wolves became domestic dogs. Collecting specimens from fur farms across the Soviet Union, Belyayev's team ran a selective breeding program based on behaviour, originally selecting for tameness and later for foxes that specifically sought human attention. Today, the experiment routinely produces generations that look and act like domestic dogs; Belyayev predicted that lower adrenaline levels would cause physiological changes, including changes to the production of melanin, resulting in the namesake "marble" or mottled fur pattern.

While the initial experiment primarily sampled silver fox morphs (believed to be the most tameable), the project has resulted in a variety of colour morphs including red, silver, platinum, and cross; despite the 'Canadian' moniker, the iconic 'Georgian White' is exclusive to the Institute.

Recently, the timeline for "domestication syndrome" observed in Belyayev's experiment has been called into question following greater attention to documentation linking Soviet silver fox farms to populations imported from Rosebank fur farm, Prince Edward Island, Canada, in 1928. PEI breeders routinely selected for friendliness and unusual fur patterns, and by the 1920s there were accounts of foxes behaviourally and morphologically similar to Belyayev's later generations. While not discounting Belyayev's work, it suggests the groundwork for domestication was laid earlier than the experiment presumed.

Further information:

• Russian Domesticated Red Fox (Wikipedia)
• Wikipedia page on Belyayev, with further details on the experiment itself
• 'The History of Farm Foxes Undermines the Animal Domestication Syndrome' – opinion paper arguing the Belyayev team's claim to effective domestication within only ten generations is inaccurate, and challenging the "domestication syndrome" hypothesis