This post is part of the series on Belyaev’s fox experiments.
(index | part I | part II | part III | part IV )

After frequently finding myself encountering references to Belyaev’s fox experiment in a number of dog-related texts, I felt the need to investigate his experiment more thoroughly.  This has resulted in a lot of reading, but a lot of new found knowledge.  From this reading, I hope to have a better understanding of the connection dog-authors are trying to make between dogs and the fox experiment. I hope it also proves useful for my readers.

The version of events in much of the dog literature is that selecting foxes for tame behaviour results in foxes developing more ‘dog like’ physical characteristics.  As such, conclusions regarding dogs have been made from this experiment.

However, a little more sophisticated version is that foxes have simply developed traits that many domesticated animals have – that is, domesticated foxes and dogs are not much different to how horses, cows, sheep, and cats have also responded to domestication.

This is the first of a series of three (or four) posts that will examine what the literature often refers to as Belyaev’s fox experiment.  This post will give a general understanding on the method of the experiment, while following posts will look at the changes found in the domesticated fox line, and their potential causes.  Finally, I will make a post to attempt to explain why this is relevant to dog science.

Belyaev’s fox experiment

This experiment has spanned 40 years, has involved 45 000 foxes, and resulted in 100 very domesticated foxes which actively seek human interaction. The fox experiment started in the 1950s.  Darwinian ideas were unpopular at the time, and fox farming was a suitable guise for Belyaev’s experimental purposes.

Belyaev described the main task of the experiment was “by means of selection for tame behavior, to obtain animals similar in their behavior to the domestic dog.” I think it’s important to note that Belyaev himself describes the main task of his experiment was to develop dog-like behaviour in the fox. Belyaev also theorised that selecting for domestic-type behaviour influences the reproductive patterns of animals.

The foundation population

Belyaev defines domestication as animals who are able to breed in captivity, and be non-fearful of man, and indeed perhaps ‘obey’ man.  He started with foxes that, even though they had been raised in a captive situation for 80 years, still had wild, undomesticated habits: their reproductive rhythm, moulting, and behaviour was ‘wild like’.  30 male foxes, and 100 vixens were the foundation stock from a fox farm.  The most tame animals from this population, and their offspring, was bred from (which was only 4-5% of the male offspring, and 20% of the female offspring).

(Click here to view a video of a farm-fox being evaluated.)

This initial stock responded to man in varying degrees.  30% were very aggressive, 20% were fearful, 40% were fearful and aggressive, and 10% were quiet and more exploratory (but were still by no means friendly, and in fact Belyaev describes them as “dangerous”).  The initial population did have some overlaps, with animals not clearly fitting into any of these groups.  However, over the course of the experiment, soon these overlaps dissipated.

Evaluating ‘tameness’

The ‘tameness’ of the foxes was evaluated by tests. Belyaev (in 1979) describes a different process of evaluation than Trut (in 1999).  My best guess is that methodology for evaluation has changed over time, and this accounts for different evaluation methods between the two authors.

Belyaev says that the foxes were tested twice at 2-2.5 months and then again at 4.5-5months, with very little variation seen between the two tests (i.e. an animal that was defensive at 2.5 months is likely to have a similar score at an older age).  The fox’s reaction to the experimenter’s presence, attempts to touch, and attempts to give it food were recorded.

According to Trut, the foxes were evaluated once a month, starting from 1 month of age and continuing until the fox was 6-7 months old.  In these tests, the experimenter offers food to the fox and tries to stroke the animal.

Regardless of the evaluative test, at the conclusion of these tests, the foxes were then given a tameness ‘score’.

1. Class III foxes would flee from man, or bite.
2. Class II foxes would let themselves be patted or handled, but were not considered friendly.
3. Class I foxes are friendly, wag their tails, and whine.
4. After six generations, they added Class IE (for “elite”).  These foxes are super eager to have human contact – they seek human attention and basically act like dogs.

By the tenth generation, 18% of fox pups were class IE, and by the 20th generation, 35% were class IE. From 1985 to the present, as the experiment continues, about 80-90% of foxes are Class IE.

Basically, each fox was tested and the foxes that were the most tame in their generation was bred to other tame animals.  This was a strict process, and only 15-20% of the population was ever allowed to breed on. They continued this process over generations, and it was just 10 years before foxes were bred who were attracted to humans.  These animals were not ‘trained’ to like people – the tameness was an innate behaviour pattern.  All contact with humans was time dosed to ensure no training occurred.

Controls & Inbreeding

This experiment also accounted for controls. Alongside the domesticated strain, selected for tameness, there was also an unselected strain and a strain selected for aggression.  These have been useful for evaluating the differences between the domesticated and undomesticated strains of foxes.

There was always concern about inbreeding in this fox population, too, and the animals were frequently outcrossed with farmed-foxes to ensure genetic diversity.

Results of Experiment

This is how Belyaev describes ‘his’ foxes: “…[The] foxes are quite tame, not as a result of training or taming, but due to prolonged selection for a tame genotype. Moreover, some quite new ethological characters have appeared, unusual even in the tamest animals bred on ordinary farms. Like dogs, these foxes seek contact with familiar persons, tend to get close to them, and lick their hands and faces. In moments of emotional excitement, they even sound like dogs. … at the sight of even a strange person, they try actively to attract attention with their whining, wagging of tails, and specific movements.”  This population is different to other farmed foxes: They are not scared or aggressive to people, and actually seek them out.

(Click here to view a video of a tameness bred fox being evaluated.)

These results have been somewhat replicated.  Kenttamies and colleagues conducted an experiment that was similar, but concerned with confidence in domesticated foxes.  Confidence was measured by how quick a fox would eat in an experimenter’s prescence.  The experiment spanned over 4 years, but, by selecting for more confident individuals, the confidence improved in just 3 years.  At the conclusion of the experiment, intensely fearful pups made up less than 10% of the selected population.  The research concluded that confidence was low to moderately inherited.

The experiment proves that tameness (and defensiveness) is a genetic trait.  This is a significant implication of this research.  However, it does not seem very extraordinary that selecting for tame foxes has resulted in a line of tame foxes in this current era.  What has been interesting is that alongside the tameness, appeared traits that were not selected for.  This includes floppy ears, changing coat colours, smaller teeth, smaller bones, curly tails, and overall puppy like characteristics – or, in other words, very dog like characteristics.  These changes and their potential causes will be examined in my next post.

References:

Belyaev, DK (1979). Destablizing selection as a factor in domestication Journal of Heredity, 70 (5), 301-308 [link]

Kenttämies, H., Nordrum, N., Brenøe, U., Smeds, K., Johannessen, K., & Bakken, M. (2002). Selection for more confident foxes in Finland and Norway: Heritability and selection response for confident behaviour in blue foxes (Alopex lagopus) Applied Animal Behaviour Science, 78 (1), 67-82 DOI: 10.1016/S0168-1591(02)00078-3

Kukekova, AV, Acland, GM, Oskina, IN, Kharlamova, AV, Trut, LN, Chase, K, Lark, KG, Hollis, NE, & Aguirre, GD 2006, ‘The genetics of domesticated behavior in canids: What can dogs and silver foxes tell us about each other?’, The Dog and Its Genome, Cold Spring Harbor Labratory Press. [link]

Kukekova, A., Trut, L., Oskina, I., Johnson, J., Temnykh, S., Kharlamova, A., Shepeleva, D., Gulievich, R., Shikhevich, S., Graphodatsky, A., Aguirre, G., & Acland, G. (2007). A meiotic linkage map of the silver fox, aligned and compared to the canine genome Genome Research, 17 (3), 387-399 DOI: 10.1101/gr.5893307 [link]

Trut, L. (1999). Early Canid Domestication: The Farm-Fox Experiment American Scientist, 87 (2) DOI: 10.1511/1999.2.160 [link] (I highly recommend this reference for further reading.)

Trut, LN, Kharlamova, AV, Kukekova, AV, Acland, GM, Carrier, DR, Chase, K, & Lark, KG 2006, ‘Morphology and behavior: are they coupled at the genome level?’, The Dog and Its Genome, Cold Spring Harbor Laboratory Press, Wdoobury, NY: 81-93. [link]

“New Nice” on the Radiolab show in October 2009. [link] (I highly recommend this reference for a light hearted, audio version of this experiment.)