Sometimes we see things so often that we simply forget to ask “why are they like that?” For instance, let’s take a closer look at domestic animals. Dogs, cats, horses, cows, pigs – animals that we live with, and who couldn’t live without us.

Common Traits

What do all these domestic animals have in common?

pb_pup pb_cat pb_dog
pb_cow pb_horse pb_pig

Now this isn’t a particularly subtle example, but that’s kind of the point. You can see that all of these domestic animals have large white patches – they’ve lost pigment in their coats in some areas. Why do we care? Well, this is something that is extremely common among domesticated animals, but very rare among wild animals. I hear you saying “but what about zebras, or any other wild animal with white patches?”. What we’re referring to here is slightly different. A zebra will always have that patterning, whereas what we’re looking at here is depigmentation – the loss of color in certain areas in an animal that is “normally” colored.

What else is common among domestic animals but rare in the wild? Well, things like dwarf and giant varieties, floppy ears, and non-seasonal mating. Charles Darwin, in Chapter One of Origin of the Species noted that “not a single domestic animal can be named which has not in some country drooping ears”. A very significant observation when you consider that there is only a single wild animal with drooping ears – the elephant.

So perhaps something weird is going on here. Why do animals as different as cats and dogs have these common traits? It seems to arise simply from being around humans!

The Hypothesis


The Russian geneticist Dmitri Belyaev provided a very interesting potential explanation. Genetics at the time was preoccupied with easily measurable traits that could be passed on – if you bred dogs, you could pick the biggest puppies, breed them, and they would produce bigger dogs on average. Fine. But that is selection of a single simple trait, something that likely did not require that many genes to “switch” in order for the puppies to be bigger.

But what if you were selecting for something more complicated? What if, instead of selecting for a simple trait like size or eye color, you selected for something more vague like behaviour – in this case, the very behaviour that made these animals more likely to be around humans. We can call it tamability, or lack of aggressiveness, or whatever – the point is, we are selecting for those animals who will behave in a manner we want around us. A wolf who does not display aggressive behaviour might be able to grab a few scraps of food from the garbage pile of a early human settlement, rather than being driven off.

And if we were selecting a complicated behaviour, rather than a simple trait, it seems likely that it will require more change in the animals genetic code. And since the genetic code is a tangled web where a small bit of DNA can be referenced in many areas of the body – perhaps selecting for a common behaviour would also cause other common traits to arise in animals that are otherwise different.

It’s like giving your car a paint job versus trying to make it go faster – the paint job is easy, but trying to make it faster could lead to your car exhibiting other traits you didn’t directly request, like consuming more gas during regular driving. This could be common across all your project cars. One is a low level trait (the paint, the size of puppy) that can be encompassed in a tiny bit of information (color, size), the other is a high level trait (speed, tamability) that must involve a wide variety of sub-systems changing as well.

The Experiment

Now if you were a Soviet scientist in the late 1950s, you probably worked on something awesome like a giant robot that shot nuclear missles, or a flying submarine. Not Dmitri Belyaev. No, he lost his job as head of the Department of Fur Animal Breeding at the Central Research Laboratory of Fur Breeding in Moscow in 1948 because he was committed to the theories of classical genetics rather than the very fashionable (and totally wrong) theories of Lysenkoism.

So instead, he started breeding foxes. Well, it was technically an experiment to study animal physiology, but that was more of a ruse to get his Lysenkoism-loving bosses off his back while he could study genetics and his theories of selecting for behaviour.


He started out with 130 silver foxes. Like foxes in the wild, their ears are erect, the tail is low slung, and the fur is silver-black with a white tip on the tail. Tameness was selected for rigorously – only about 5% of males and 20% of females were allowed to breed each generation.


At first, all foxes bred were classified as Class III foxes. They are tamer than the calmest farm-bred foxes, but flee from humans and will bite if stroked or handled.


The next generation of foxes were deemed Class II foxes. Class II foxes will allow humans to pet them and pick them up, but do not show any emotionally friendly response to people. If you are a cat owner, you would call the experiment a success at this point.


Later generations produced Class I foxes. They are eager to establish human contact, and will wag their tails and whine. Domesticated features were noted to occur with increasing frequency.


Forty years after the start of the experiment, 70 to 80 percent of the foxes are now Class IE – the “domesticated elite”. When raised with humans, they are affectionate devoted animals, capable of forming strong bonds with their owner.

These “elite” foxes also exhibit domestic features such as depigmentation (1,646% increase in frequency), floppy ears (35% increase in frequency), short tails (6,900% increase in frequency), and other traits also seen frequently in domesticated animals.

The Results

Belyaevn passed away in 1985, but he was able to witness the early success of his hypothesis, that selecting for behaviour can cause cascading changes throughout the entire organism. For instance, the current explanation for the loss of pigment is that melanin (a compound that acts to color the coat of the animal) shares a common pathway with adrenaline (a compound that increases the “fight or flight” instinct of an animal). Reduction of adrenaline (by selecting for tame animals) inadvertently reduces melanin (causing the observed depigmentation effects).

So if Belyaevn is right, genetics is not just a low slow process that works on tiny incremental tweaks. Complicated environmental pressures can result in complicated genetic results, in a stunningly quick period of time. Where do I think we’re going with this?

Well, designer pets for one. Following the collapse of the Soviet Union, the project ran into serious financial trouble in the late 1990s. They had to cut down the amount of foxes drastically, and the project survived primarily on funding obtained from selling the tame foxes as exotic pets. Imagine a menagerie of dwarf exotic animals, who crave human attention and form bonds with people. It would be obscenely profitable.

And the out there thought for the day? We’re doing this to ourselves. We don’t encourage people to act aggressively all day to everyone they meet. We reward certain behaviours more than other behaviours. My unprovable conjecture? Humanity is selecting itself for certain behaviours, and the traits we think of as fundamentally human (loss of hair, retention of juvenile characteristics relative to primates) are a side effect of this self-selection.


Here are some great videos with footage of the tame foxes.

From NOVA – Dogs and More Dogs (starts at about 17:30)

“Suddenly, it all started to make sense. As Belyaev bred his foxes for tameness, over the generations their bodies began producing different levels of a whole range of hormones. These hormones, in turn, set off a cascade of changes that somehow triggered a surprising degree of genetic variation.

Just the simple act of selecting for tameness destabilized the genetic make up of these animals in such a way that all sorts of stuff that you would never normally see in a wild population suddenly appeared.” (Full transcript)

68 thoughts on “Clever as a Fox

  1. There is a evolutionary biology sub discipline called heterochrony. It studies the rate and timing of maturation and developmental changes as these adjustments influence species evolution. The heterochronists offer a fairly vast literature that informs these fox studies. Matsuda, recently diseased, is perhaps the most powerful contemporary proponent of this point of view.

  2. Very interesting, as breeding for tameness produced these other side effects. Just a curiosity, what would be the side effects of doing the opposite (breeding for aggression)? I’m sure there’s been experiments to that effect (i.e. guard dogs?), however the full outcome may not be as expected. Also, the question of whether breeding for aggression back into these foxes would revert back the melanin levels, floppy ears, and reliance on humans, in future generations. Just curiosities of mine, of which I’m going to look into.

  3. I think this is awesome. I am a owner of a red fox from a breeder and can see those domestic characteristics from those foxes in mine. I love him and I am happy to know how they can be actual pets as those one are.

  4. I read something about that experiment several years ago, but couldn’t remember any specifics and had had trouble finding it since then.

    Thanks to you and StumbleUpon!

  5. Yes, neoteny is basically what is occurring, but to say that raising them in a static environment causes neoteny and that’s how this occurred is a bit shortsided. The statement you make is heavily reliant on the concept that continuous exposure to a lower stress environment (which I think is a more important factor than the loose and subjective ‘non-natural’) causes neoteny. While there are some correlations, there are far more studies to suggest that neoteny is essentially a byproduct (and a desirable one at that, when breeding for human companion and use animals) of other genetic occurrences due to selective pressures.

    Furthermore, neoteny is frequently observed in animals with selective behavior pressures applied to them that ARE raised in what you might consider more natural environments. For exampele, many of the desirable characteristics one would find in dogs are associated with neotenic characteristics, and one could make an argument that this would prevail, even if you raised several generations of dogs in a ‘natural’ environment.

    However, one could also argue that raising dogs in say, the wild conditions that shaped wolves over generations, would eventually return a dog into an animal with a wolf like appearance and repertoire of behaviors, given enough time, and, that the animals did not all die out from the sudden change in environmental pressures.

    While neoteny is certainly being observed in the case of the farm fox experiment, what was really learned from the experiment was the genetic relatedness of behavioral predispositions and phenotypic characteristics, in both of which the changes that were observed in the farm fox experiment may be considered to be neotenous tendencies.

  6. Reply to AndyF’s
    “It would seem that differential reproduction is creating a species of humans that are more gullible and weaker-willed. By encouraging large families, religious orthodoxy will turn the species into a less wooly version of sheep.”

    I’m sure that “differential reproduction” is causing a small subset of weaker inbred, but gullible and weaker-willed humans? Wildly differing Liberal vs Conservative mindsets amongst siblings indicates environmental influences play a far greater role in encouraging large families and religious beliefs. A balancing of all reproduction and environmental factors will eventually keep some man at the top of the food chain.

  7. Whenever possible, women do select men that show economic & or social success for mates. Societies in which the woman’s parents choose, still select for economic & or social success. There definitely is a cultural link between reward and the ability to reproduce.

  8. There are more examples of rewarding specific behaviour with reproduction in nature. It’s quite common actually. Consider the bowerbird:

    Vogelkop Bowerbird

    Satin Bowerbird

    Bowerbirds Ptilonorhynchidae

    Beyond that, ask any woman, or a guy who’s had to spend a night or two on the couch! Reproduction is absolutely a reward for desirable behaviour. To believe otherwise is not only delusional, it’s bordering on misogyny, IMHO.

  9. Perhaps. The issue is the definition of aggressiveness. Your argument regarding aggression in business is invalid if we take the entire range of aggression into consideration.

    Violent aggression tends to result in early death or incarceration (often during the person’s reproductive prime). There are types of aggression we as a society have ‘selected’ to be undesirable and individuals who display these types of behavior I would argue do NOT have the same measure of reproductive success as compared to the general population.

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