The Belyaev Fox Project

In 1959, Russian geneticist Dmitry K. Belyaev set up an experiment on the silver fox (Vulpes vulpes). Belyaev hypothesised that an animal’s ability to be tamed (their tamability) was a determining factor in the course of domesticating animals. He designed a selective breeding programme, selecting silver foxes for their tamability and against aggression. The study started with 30 male foxes and 100 vixens. Notably, these foxes were somewhat tamer than completely wild foxes as they had been farmed. The criterion for selection was exclusively tameness. The experiment continues to this day and has established some fascinating results. 

Behavioural Changes

The behavioural changes in the foxes selected for tameness has been dramatic. Initially, foxes had been assessed for tameness once they hit sexual maturity and placed into one of three classes, with class 1 foxes being the tamest who were friendly to humans and class 3 foxes being the least tame, those who avoided human contact. Within 6 generations, a new class had to be included, known as the ‘domestic elite’. These foxes actively sought out human interaction, whimpered, sniffed and licked the experimenters. By 1999, 70 to 80% of the foxes in the experiment were considered to be ‘domestic elite’ (Trut, 1999). 

As well as being more tame, a 2005 study by Hare et al found that fox kits from the experimental population were as skillful as dog puppies in reading the expressions and gestures of humans. This is likely a by-product of selective breeding for tameness. The study found that the control group of fox kits not bred for tameness were not as skilled at reading humans as the experimental population. This suggests that the selective breeding of the foxes has significantly affected their social emotional evolution. 

Physical Changes

Selective breeding for the behavioural trait of tameness also led to significant changes in other areas of the foxes development. Within just a few generations, some of the foxes in the study had floppy ears and curly tails (Dugatkin, 2018). These traits are not seen in wild silver foxes. Indeed, floppy ears are not seen at all in non-domestic animals, apart from elephants. Changes in the coat colour and markings of the experimental population were also observed. White spotting on the head, known as piebald, began to appear. Selection for tamability also appears to have had an important impact on the reproductive behaviour of the foxes. Whilst foxes in nature breed just once a year, mating occured outside of the usual reproductive season for the domesticated foxes (Trut, Oskina & Kharlamova, 2009). 

The Belyaev Fox Project produced a number of interesting results. Selectively breeding for tameness not only influenced the foxes behaviour towards the human experimenters significantly, it also appears to have affected their social emotional evolution, their physical appearance and their reproductive habits. Belyaev’s experiment on silver foxes is relevant to our understanding of canine domestication as it may give us some insight as to how domestication occured. 

What the Belyaev Fox Project tells us about dogs

Given our current understanding that early dogs were likely drawn to human groups to obtain food, it is feasible that tameness would have been a trait passed down through generations. This is true even within natural selection, as the tamest dogs would have acquired the most food from humans. It would make sense then for humans to begin artificially selecting for the tamest dogs. This dogs would have been the easiest to train for specific functions and as companions.  

Much research has been undertaken to further understand the specific processes by which domestication occured in dogs, as well as other mammals. It was Charles Darwin who first posited ‘domestication syndrome’ (Darwin, 1868). This refers to the behavioural and physiological traits shared by a number of domesticated animals and not seen in their wild counterparts, such as floppy ears. Wilkins, Wrangham & Fitch (2014) proposed that domestication syndrome resulted from neural crest cell deficits that occured during the development of the embryo. Most recently, Gleeson & Wilson, 2023, proposed that changes seen across multiple domesticated species occured due to shared disruptions to the reproductive patterns throughout the process of domestication. One of the disruptions suggested by the authors was that selection causing tameness disrupts male to male competition for female mates. This is particularly interesting as it was tameness that was specifically selected for in the Belyaev Fox Project. It may explain some of the changes to the silver foxes reproductive behaviour. 

Differences between dogs and foxes

There are significant parallels between the behaviour of the silver foxes after several generations in Belyaev’s study with the domesticated dog. Whilst the process of canine domestication took substantially longer, it’s likely that there may be similar genes involved in both species (Kukekova, Trut & Acland, 2014). A study by Kukekova et al, 2007, sought to compare the canine genome with that of the silver fox. They investigated the linkage maps -these provide a relative location of genetic markers on a chromosome. They found a high rate of genomic sequence identity between the dog and the silver fox.

However, there is far more to the domestication of dogs than just human input. Whilst there are parallels between the domestication of modern dogs and the foxes in Belyaev’s study, we must consider that the study was done under highly controlled experimental conditions. Conversely, a number of factors may have also contributed to the domestication of dogs aside from just human selection, which started thousands of years ago and is an ongoing process. These include climate, environment, mutation, diet, disease and architecture and more (Losey, 2021). None of these factors operate in isolation and may have impacted the process of canine domestication to different degrees at different times. 

The Belyaev Fox Project

In conclusion, Belyaev’s study on silver foxes can provide us with some insights into canine domestication. Further investigation into domestication syndrome and the potential shared genetic profile of the silver fox and the modern dog are needed to fully analyse just how much Belyaev’s study can inform our understanding of canine domestication. The multitude of other factors likely involved in the domestication of dogs should also not be discounted. 

References

Darwin, C. 1868. Variation of Animals and Plants Under Domestication. 

Dugatkin, Lee A, 2018. How to Build a Domesticated Fox: The Start of a Long Journey. The Chautauqua Journal: Vol. 2 , Article 23. 

Hare, Plyusnina, Ignacio, Schepina, Stepika, Wrangham & Trut, 2005. Social Cognitive Evolution in Captive Foxes Is a Correlated By-Product of Experimental Domestication. Current Biology, Volume 15, Issue 3. 

Gleeson, BT., & Wilson LAB., 2023. Shared reproductive disruption, not neural crest or tameness, explains the domestication syndrome. Proc. R. Soc. B.

Kukekova, A., Trut, L., & Acland, 2014. Genetics of Domesticated Behavior in Dogs and Foxes. Genetics and the Behavior of Domestic Animals. 361-396. 

Kukekova, A. V., Trut, L. N., Oskina, I. N., Johnson, J. L., Temnykh, S. V., Kharlamova, A. V., … & Acland, G. M. (2007). A meiotic linkage map of the silver fox, aligned and compared to the canine genome. Genome research, 17(3), 387-399.

Losey, R. J. (2022). Domestication is not an ancient moment of selection for prosociality: Insights from dogs and modern humans. Journal of Social Archaeology, 22(2), 131-148.

Lyudmila N. Trut, 1999. Early Canid Domestication: The Farm-Fox Experiment. American Scientist, Volume 87

Trut L, Oskina I, Kharlamova A. Animal evolution during domestication: the domesticated fox as a model. Bioessays. 2009 Mar;31(3):349-60. 

Wilkins AS., Wrangham RW., & Fitch WT.,  2014. The “domestication syndrome” in mammals: a unified explanation based on neural crest cell behaviour and genetics. Genetics. 197(3):795-808. 

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