Clever as a Fox
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?
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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.
Videos
Here are some great videos with footage of the tame foxes.
From NOVA – Dogs and More Dogs
“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)
From Discovery Channel – The Ultimate Guide: Dogs
The start of the video to about 0:40 shows you just how well these tame foxes integrate in a family environment.
A very good read. Very interesting.
i agree. very good read.
One word: neoteny. The environment that you raised the foxes in was less rough than the natural environment so they simply retained their juvenile traits.
“Humanity is selecting itself for “tameness”, and the traits we think of as fundamentally human (loss of hair, retention of juvenile characteristics relative to primates) are a result of this self-selection.”
Fail. We would only be “selecting” something if those who had the undesirable trait (ie aggressiveness) were having less reproductive success. This is not the case. There are plenty of areas where aggressiveness is rewarding. The business world for example. They have money, and have babies.
Very good read – The human selection part is something I have been thinking about for quite some time. It has a huge impact on the future of the species and planet in general. Tie that in with the long term effects of many of the chemicals we use without knowledge of their long term effects and you have a pretty crazy little genetic circus coming to town. Thanks.
RE: last paragraph
Another, very convincing theory on hairlessness is that it’s a result of our bipedal gait. As savannah animals, our ancestors would have been continuously exposed to blasting sun. For four legged animals, fur provides a protective layer against the sun as their whole bodies are exposed. Once man went bipedal, only a small part of our bodies were exposed, which is the one of the few places we still have loads of hair. We lost it on the rest of our bodies because it also acted as insulation (i.e. stopping heat leaving the body). Humans have the best heat loss system of all animals, in that in sweat profusely. Fur would impede this, holding the heat we were trying to loose close to the body. This ability to loose heat quickly meant we could run for long distances at a moderate speed. May not seem like much, but most animals overheat quickly and have to stop running. If your pray can only run for 4 hours and you can run for 5, then you’ll be eating tonight.
References:
The hair thing was from
Horizon’s What’s the Problem With Nudity? on BBC 2 in the UK.
The running thing is http://discovermagazine.com/2006/may/tramps-like-us
@Matt – are you saying that white(r) skin is a juvenile trait of humans? The connection between your second and third sentence is suspect, at best.
Matt:
Neoteny doesn’t explain it. If it did, the same degree of “juvenile tameness” would have been evident with Generation I— it wasn’t. Neoteny is a conditioned behavior, independent of the genetic behavior they were selecting for.
As others have already stated – an excellent read. ^^ I wish I had something more interesting to add.
The conclusion is faulty. There’s no obvious link between what you call “reward” and the ability to reproduce. Economic and or social success isn’t necessarily the same as reproductive success.
Very very good read. I agree with Eroglik however. Having said this your post really has me thinking and now Im intrigued to talk about this pigment issue with my professor Monday
Very interesting article. Although you may want to pick up a Canadian (or Oxford standard English) dictionary so you can avoid US spellings of things like ‘colour’ or ‘centre’.
Great read though, excellently researched.
I don’t think that tameness is necessarily genetically tied to the changes in pigmentation. It seems more likely that domesticated animals are protected from the forces that normally select against having giant “look at me” spots all over.
So – this does tie directly to humans, but doesn’t explain our hairlessness. The more we domesticate ourselves, the more we protect members of our species who have maladaptive traits because letting them die isn’t friendly. Nearsightedness comes to mind.
very interesting. this study intrigues me.
anthony Pittarelli
[...] is a fascinating article, Clever as a fox, on the domestication of animals and the Dmitri Belyaev fox experiments on [...]
Great research and awesome post! Ignore the detractors: they post to see their own words in print and are about as effective as painting your car to go faster!
I, for one, do think that sociability and lack of agressiveness will lead to higher reproductive success, just like intelligence.
In the highly violent world of the past, only the people who worked together could successfully protect themselves from outside aggression, while maintaining the high food production needed for feeding, breeding and freeing up labor for toolmaking and invention. This pattern has been the same for essentially all of history, including the current era. Any culture capable of successfully waging war without destroying itself from the inside will have significantly higher reproductive success than the cultures that are being conquered and decimated. The cultures who encouraged cooperation, honesty, patriotism (or religious adherence), personal freedom and intelligent decision making (on a personal and national level) would have a huge advantage. The cultures with different priorities would be out-competed unless sufficiently isolated from their neighbors (f.ex. Tibet)
Just look what is happening to the aggressive (or inefficient) civilizations who’ve had to compete with the western world this century. All indigenous populations have been reduced to foreigners in their own lands. North Korea is starving itself to death to maintain military sovereignty. China is (slowly) adopting capitalism and democracy. Iran and Iraq have been decimated, The muslim. The USSR was decimated economically, like North Korea. Nazi Germany was efficient, but overly agressive, and that culture was also eradicated.
I guess the upshot is that evolution acts on both cultural traits and the people within the culture. It is eminently possible that our culture and traditions have been shaped to promote the kind of people who facilitate efficient cultures.
Just my 2 cents anyway.
Maybe its just the result of copious amounts of inbreeding. The animals got stupid. Short tails, floppy ears, etc are recessive traits coming to the surface because of the inbreeding.
Still, it’s really interesting. I’d love to have a retarded, inbred mutant fox for a pet.
>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.
A word to the wise. If you don’t know about something, don’t talk about it. It just undermines your credibility.
>>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.
>A word to the wise. If you don’t know about something, don’t talk about it. It just undermines your credibility.
A word to the overly sensitive. I believe the author was using something called humor, and was quite successful at it too.
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.
now if only they would do the same to lions and tigers…
Interesting read! Thanks.
From a human standpoint, we are probably at the apex of the small family or childless moment. Women who are prone to having children pass on their genes. Look for a boom in large families and human population in the future as the child-less inclined weed themselves out of the gene garden.
You should read A Farewell to Alms by Gregory Clark. He has a theory of the evolution of Imperial Man into Modern Economic Man, seeking to explain why Europe exploded with commerce and trade in the 18th century while the rest of the world remained much like ancient Greece or Rome.
Sheri S. Tepper’s book Gate to Women’s Country has post-apocalyptic women selecting men this way.
Very interesting to read, thank you.
I want a Fox now… Where can I get one?
Interesting research, though I don’t think the conclusion lends itself to the human population because we do not have the level of control on birth and death of human as we do with foxes. No framework has existed with clarity, consistency and persistence long enough to produce observable results. Most “experiments” such as eugenics, war, or one-child policy, generally last less than 1 generation. Even with respect to violence, while aggressive individuals are disadvantaged in certain situation (crime), they are encouraged in others (military, law-enforcement, business…). Criminals (even incarcerated ones) still have children.
A more interesting perspective on human self-selection is the one promoted by Wolfram, who saw population of character traits exist in an ecosystem and in stable equilibrium. Aggressiveness confers reproductive advantage, but only to a certain point. If sudden changes in the environment magnify that advantage and result in reproductive success, the resulting increased aggression in the environment will nullify the previous advantage. That’s the problem with self-selection within a population: as soon as a trait emerge, the next generation are filled with it, and then it’s no longer an advantage.
Would be interesting to see how human evolution will be affected by genetic technology, when you can change your gene as you see fit, or screen the next generation with greater control. Perhaps even create specialist co-evolving species based on human?
1. Cats don’t have floppy ears. Only a very, very small set of breeds do.
2. Pigmentation (or, as you mention, depigmentation) might have more to do with natural selection, where the environment dictates which traits survive based on which animals survive. Polar bears, for example, would fare better in the arctic if they are white, but given a comfortable human environment where there is little or no selective pressure, genetic variations can and will be more common.
3. Your article suggests that domestication may be a genetic factor, but in all my experience, domestication has more to do with the learned reliance on human care. This is bred – not in genetic terms but in terms of animal sociology. Just as babies learn how to act in this world from their parents and their environment, the same is true for animals.
Putting on my skeptics hat, I would have to say that this article (or the research it is based on) is discussing a theory which is based on the flaw of correlation implying causation.
wild horses have patches…
nice post… interesting read.
> Cats don’t have floppy ears. Only a very, very small set of breeds do.
http://www.messybeast.com/foldear-cats.html
> but given a comfortable human environment where there is little or no selective pressure, genetic variations can and will be more common.
1600% more common within a few generations? Putting on my skeptic’s hat I’d say you are reaching.
> Your article suggests that domestication may be a genetic factor, but in all my experience, domestication has more to do with the learned reliance on human care. This is bred – not in genetic terms but in terms of animal sociology.
http://en.wikipedia.org/wiki/Tame_Silver_Fox
Read the part on genetic differences.
Better yet, do some research before spouting off.
[...] rävar, evolution, domesticering http://www.gmilburn.ca/2009/03/20/clever-as-a-fox/ [...]
Very interesting post! I´ve linked to you in my blog.
Like DW, I’m a bit skeptical that modern societies select for non-agressive behavior. For one, almost every generation has had a substantial portion of its young men fight in war. I’d imagine that most of the world population is less than 4 generations from an ancestor who killed people.
Second – if assertiveness and aggressiveness are on the same spectrum, then our society certainly selects for SOME aggressiveness. Plenty of thrill seekers and risk-takers have great success producing offspring. The foxes mentioned here were the bottom 5% or 20%. In modern human society, I’d imagine that the least aggressive actually have greater trouble reproducing than the most aggressive. The “most successful” quintile would probably be the 3rd or 4th. And of course, I have no hard data – this is just a thought experiment.
But anyway, the most aggressive people in a modern western society may not necessarily be criminals. Plenty will find a way to channel aggression into sports, business, or other competition. Cops, soldiers, and professional athletes have children, too.
It is testosterone and copper for pigmentation.
In just the way that Budiansky selected for tame behavior, human societies have found ways to select for specific features.
Female infanticide provides a patrifocal society the leverage to sexually select for a narrow window of macho male personality types, upholding cultural stability, curtailing innovation.
Female infanticide is a manifestation of sexual selection in a cultural context. Female infanticide can be understood as patrifocal, cultural acceleration and/or stabilization. By decreasing the number of women to less than the number of available men and by being more specific about features that can be chosen for in the character and genes of the males, the more culturally rigid, both in terms of cultural ideas and the genetic pool, the culture will continue to be.
A culture keeps tight control of its degree of diffusion or drift by maintaining a low female/high male ratio. This control results in a shift toward a selection of highly specific traits. As a culture starts to idealize war, the families of those women or their fathers choose a mate based on success-in-war criteria. Female infanticide decreased the number of men likely to create progeny, increasing the likelihood that the warlike criteria would be passed on to the next generation. With a high percentage of young men who are potentially mateless, aggressive posturing abounds, violent confrontations increase and opportunities for men to show their “character” emerge. The successful men will be rewarded with a mate or mates.
In a sense, the ship of state can steer left or right, depending on how many girl babies are thrown overboard.
Embrace the female. Innovation can proliferate as criteria for the perfect mate can vary as a larger number of young women can choose from a wider variety of men.
Suppress the number of women by killing them as embryos or babies. Then fewer men can sire a child and only those highly valued, aggressive male personalities can achieve a mate. In a patrifocal society, those highly valued males can often effectively wield authority and obediently serve the established hierarchy. Creativity is not their strength.
Contrary to what the neo-Darwinists and sociobiologists would suggest, evolution is a lightning fast process driven often by sexual selection, often by abrupt changes in the rate and the timing of maturation. When prolonged, these changes in rate and timing are called neoteny. One way we have been controlling our own evolution is by committing female infanticide. Another way we direct how society transforms is by choosing mates for their nonviolent, creative, cooperative tendencies.
As Budiansky showed, the selective process can move in the opposite direction.
We humans, particularly women, are selecting tame humans, cooperative males, and changing our species in the process. Whereas female infanticide steers society toward hierarchy, male posturing, stability and war; females selecting cooperative, creative, sensitive to interdependence, independent males construct a society that is open to change.
In the way that foxes can be transformed into dog-like creatures in a mere 20 years, humans are in the process of transforming each other by picking mates for their cooperative inclinations.
Clearly, if we’re going to survive the next 100 years, it’s the males that have to change.
See http://www.neoteny.org/?p=359, http://www.neoteny.org/?p=232 and http://www.neoteny.org/?p=17 for one page variations on this theme
Stephen J. Gould wrote a lot about neoteny in different species, particularly humans.
They have some silver fox videos on youtube , yes, Belyaev’s foxes.
From discovery channel
http://www.youtube.com/watch?v=oDb27ZP9zEE
[...] Clever as a Fox – very interesting article on domestication, with some interesting implications regarding human self-domestication. [...]
If it had been my experiment, I would have also bred together the top percentages of the most aggressive foxes, but had them rely on humans the same way the least aggressive and the control had to, to account for the “nurture” factor in the experiment. Also, it may have accounted for depigmentation being a cause of inbreeding (if the most aggressive foxes didn’t depigment, but were bred the same way, it is most likely a domestication issue).
I can, however, see why Belyaev didn’t want 30 crazier-than-usual foxes sitting around though.
Where to start,,,,
1. To the author, a very interesting article. The experiment may not have been as controlled as our 7th grade life science teacher’s would have liked, yet that does not exclude the general conclusions to be made.
2. ears and spots on domesticated animals can be signs that although are not present in all domesticated animals, is a sign of their domestication. having such animals interact with wild ones of the same species would be a good experiment. see how much they get pushed around in the first five minute of their interactions.
3. leaving aside spots and floppy ears, you can go to any local zoo and see the lion, king of the jungle (or saharan plains more likely) and see his/her droopy eyes and lazy demeaner to know he has been beaten down. not domesticated, still dangerous. but send him back to the wild, and he will be the last lion in africa to get laid.
nature vs. nurture, an individual’s or animal’s environment will push the limits of its heredity.
on to us humans,,,,
1. highschool girls will most probably in any sort of test go for the bigger stronger males, not neccesarily jocks, but more physical ability then mental ability, future income, good family and all that jazz
2. the same girls grow up to be women, who through dating experiences come to perceive strength in potential partners in a different light; much less pure and animalistic, more with their heads then their hearts lets say. case in point, ask women you know, and women ask yourselves: “would you feel more safe with mike tyson or tyson’s lawyer?
if the world ended, the revolution succeeded and every man was for himself, then tyson would start looking like a much more attractive mate.
in our western lands of endles starbucks and strip malls and well lit streets, security cameras up the az$ (chicago is about to be completely camera-covered along with london, england), a Good Lawyer is All you Need!
i believe the mentally agressive males, are the new kings of the human jungle. women still prefer strong men, they just do not end up with them as long term commitments require more then good orgasms.
our society has definately made that possible. strength, honor, honesty, shivilry, are no longer the most desired or required characteristics.
to Johann Erdogan and his benign comments above:
you are extremely mis-informed on all current political status:
1. the only people who won the war in iraq are the american oil & gas companies (i know as i work for them, yes i sold my soul)
2. iran has been giving the west the finger throughout 8 years of the bush administration, and have not seen one single action to shake them; they did however work very closely with the Bush administration in sharing intelligence about the Taliban in Afghanistan, yes the u.s. and iran were working together while bush was feeding us all crap about axis of evil.
3. russia is an extremely wealthy country that is more self-reliant then the u.s. and them messing with georgia recently with no one to stand in their way, is proof they still are a threat to the u.s. if they chose to be. and don’t think the europeans can help on that front, as russian gas keeps eurpeans’ butts warm every winter.
4. did you ever ask yourself where bush got $.75 trillion for his bailouts, and now obama is stacking it up to close to 2 to 3 trillion? i will give you a hint: hilary clinton was over there not too long ago on her knees begging for more money for all of us, so we don’t all have to stand in long lines to get a daily dose of govt sponsored stew surprise to stop from starving,,, CHINA! you guessed it! the west winning the cold war was all a sham. as i type this hundreds of chinese millionaires and billionaires are buying up property all over our beloved 50 states. also, ultimately what is required to get us out of this economic cluster-f is a little dose of socialism, long live king obama!
5. Islam still remains the fastest growing religion in the world, still beating out atheism.
hope this helps in our quest to find out more of how our daily lives may well be going in the wrong direction. foxes may be extinct by the time we figure out what to do.
*sorry for my atrotious spelling, i am of the spell-check generation
I’m seeing a lot of misconceptions in this discussion about how natural selection works; either that, or lot of resistance to the idea that humans are susceptible to the forces of evolutionary change. As for the final “out there” thought, the author is entirely correct. We are selecting for traits in ourselves, even if the results aren’t as predetermined as with domesticated animals.The results may be surprising and counterintuitive.
For example: Consider who has the selective advantage in contemporary society: the rich, the middle class, or the poor? Tough question, isn’t it? I’m afraid we can’t answer that one now, too many variables in play. However, it has been shown through evolutionary genetics that evolution occurs in spurts rather than gradually, and these spurts of speciation and phenotypical changes in the population coincide with environmental change. The human race has undergone more environmental change in the last one hundred years than most species go through in a million years.
Were H. sapiens to continue indefinitely without annihilating itself, I imagine speciation would occur along class lines, much like in “The Time Machine” by H.G. Wells, and other sci-fi works. Hardly an original thought, but an intriguing one.
The only issue I’m really having problems understanding is the Adrenalin/melanin connection. Melanin causes different skin tones/colours in humans, so wouldn’t that mean people with higher adrenalin levels have darker skin? But it seems to me that this relation is not really present.
Also, think of polar bears or other creatures who’s colouration is based on camouflage. Their melanin levels are surely not based on adrenalin.
I found this whole article terribly interesting! I’m definitely going to have to look into this more!
I’m not sure ‘genetic variation’ is what’s occuring here, instead what seems more likely is changes in hormone levels causing significant changes in the regulation and expression of genes, resulting in phenotypes uncommon in animals with ‘wild’ hormone levels.
Some ongoing genetic research in the Animal Science department of my university might shed some light on how breeding for behavior has an inevitable phenotypic effect.
For every trait selected for there will be correlated genetic effects. These are referred to as positive and negative correlations, depending on whether they are complimentary or detrimental to another trait. This can be seen in all familiar dog breeds. Dogs bred vigorously for very specific physical traits are less healthy or intelligent than dogs bred for more general performance.
Because of the metabolic similarity of all life on Earth, particularly species within the same Phylum, a gene in one species often has a near identical parallel in another species. Study of human behavior genes has enabled us to observe the effects of these genes where they exist in domesticated animals. DRD4 (Dopamine receptor 4), for example, is a gene responsible for emotionality in mice, curiosity and vigilance in horses, and aggression in dogs. Possibly the very gene Belyae was interested in. Breeding for a particular allele of this gene would skew the natural frequency of the allele in the population, and as behavior changed, so would correlated phenotypic effects. Drooping ears, shorter tails, etc. crop up in many domestic species because they are involved in the same metabolic pathway, influenced by the same behavior genes.
If Belyae’s foxes had become tamer as a result of continued human contact there would have been no physical change. Habituation differs from temperament, in that it is learned, not “instinctive” (bred). Also, this breeding is not natural selection choosing those animals who interacted best with humans to reproduce. Domestic animal breeding is artificial selection, and is not a function of evolution.
[...] It all has to do with adrenaline! More details: Clever as a Fox [...]
[...] How many generations does it take for traits to solidify? 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. [...]