Category Archives: The Origin of Dogs

02/11/11

Belyaev’s Fox Experiment – Changes – Part II

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

Animals, within the same species, can be truly varied.  Dog breeds, from Papillions to Greyhounds to Shiba Inus, are all the same species.  Belyaev commented: “Domestic animals differ from their wild ancestors, and from each other, much more than do some species and even genera.” This diversity is also seen within foxes, as there is a genetic difference between the ‘urban fox’ and the ‘rural fox’.  This is the same species, but they are significantly different because they have adapted to specific niches.

This difference was also seen between Belyaev’s selected-for-tameless line (‘the domesticated fox’) and unselected lines, as outlined below. These traits are still rare, however, with only ‘a few’ occurring out of every 1000-10000 individuals. These traits are not extraordinary, either, as these changes are typical of domestication in many other species.

 

Colour changes

Coat colour changes was the first change documented in the domesticated stock, in around the 8th-10th generation. Domesticated foxes are 1646% more likely to have depigmentation, 423% more likely to have brown mottling, and 400% more likely to have grey hairs, than their undomesticated cousins.  The colouration can be from patches of white on their foreheads, to spots of various colouration throughout their body, and piebaldness.

Drop ears as seen in domesticated foxes - Photos © Ruthless Photos

Drop ears as seen in domesticated foxesPhotos © Ruthless Photos

 

Floppy ears

Drop ears were observed around the 8th-10th generation.  Domesticated foxes are 35% more likely to have floppy ears than unselected farm foxes.

 

Tail changes

Tails changed position around the 8th-10th generation, with tails ‘rolled’ over the back.  Shorter tails were also observed, but at a later generation, approximately 15-20 generations into the experiment.  Domesticated foxes are 6900% more likely to have a short tail, and 1033% more likely to have a rolled tail than undomesticated farm foxes.

 

Reproductive Changes

Domesticated foxes reach sexual maturity earlier, give birth to larger litters, have a longer mating season than their unselected cousins.  However, there has not been any pups successfully reared to adulthood from an extaseasonal mating.  Many times the mating do not take and, when they do, the mothers are often cannibalistic.

 

Skulls and teeth

The domesticated foxes have smaller cranial height and width, and shorter/wider snouts than unselected farmed foxes.  Males also have a more feminine head (i.e. there is no clear difference between the sexes in terms of their head shape anymore).  Skulls in the domesticated fox are unusually broad for their length.

In regards to teeth, the domesticated foxes have smaller teeth than the unselected farm foxes.  After the 15th to 20th generation, underbites and overbites became apparent.

 

Hormonal changes

There are number of hormonal differences found in domesticated foxes, in comparison to the unselected foxes.  To put simply: Domesticated foxes have more serotonin (which is responsible for inhibiting aggression and generally ‘feeling good’).  This probably is responsible for the domesticated foxes having less ‘stress hormones’ in their system – because of the serotonin, they are less stressed.  As hormones have a rather complex and far-reaching role in development, it is probable that these results have implications across the animal.

The slightly more complex version of events:

Domesticated foxes have more serotonin, and more enzymes involved in the production of serotonin.  Serotonin is made by the liver and regulates mood, digestion, memory and learning, among other things.  In the foxes it is believed to inhibit aggression and development.

Corticosteroid levels, cortisol, and adrenocorticotpric hormone are all found in reduced levels in the domesticated fox.  These hormones come from the adrenal gland and the anterior pituitary gland in response to stress.  As these foxes are less stressed, they do not produce so much of these hormones.  Overall, domesticated foxes have less activity in their adrenal gland.  Additionally, the developmental spike in corticosteroid levels in domesticated foxes occurs much later than their undomesticated counterparts.

There are also changes in the level of steroid sex hormones, chiefly estradiol and progesterone in the domesticated foxes.  The role of progesterone in embryogenesis (development) is also significant.

Domesticated foxes became hormonally more relaxed - Photos © Ruthless Photos

Domesticated foxes became hormonally more relaxed – Photos © Ruthless Photos

 

Changes in the socialisation period

We know socialisation plays an important role for dogs, and it seems the same is the case in foxes. There is a ‘sensitive’ period of socialisation in post-natal development.

Is clear is that the domestication process in foxes has resulted in a different, extended socialisation period.  Firstly, they respond to sound two days earlier (and open their ears quicker) and open their eyes one day earlier (and also open their eyes quicker) than unselected foxes.  The socialisation period of the domedicated fox closes 3 weeks later than non-domesticated lines (i.e. the unselected foxes have a socialisation period of 40-45 days, while unselected foxes have a socialisation period of 60-65 days). Domesticated foxes have accelerated maturation intitially, and then this is retarded.  This means that foxes have an extended window, which allows them to learn more about human ways and how to respond to them.

Belyaev experimented with fox cubs from domesticated lines and lines selected from aggression.  From day 30 onwards, differences in the pups were clear.  Domesticated fox pups are more likely to move around in a new environment than aggressive lined fox pups.  But it is from day 40 that the most difference is seen.  Domesticated fox lines are less fearful, and more willing to overcome the fear in a new environment.  Aggressive lined pups were inclined to hide in a corner during the testing period – hunched, scared, and sometimes snarling.  This kind of fearful behaviour exacerbates difference between the lines, as fearful pups interact less with the environment and so have more foreign items to be afraid of in the future.

 

Other Difference

Domesticated foxes sound different (they sound ‘doglike’), they experience excitement urination, they have thinner bones, and moult in different ways to unselected stock.  Around the 15th to 20th generation, shorter legs were seen. Fox puppies from the domesticated line also respond to human cues (such as pointing) “as skilfully” as dog pups.

 

Pedomorphosis

Overall, these traits all fit into the descriptor of ‘pedomorphosis’.  This is the term to describe the retention of juvenile traits in adults.  This includes physical changes (in this example, the skull shape) to behavioural changes (such as whining and barking). As these foxes reach reproductive maturity despite the pedomorphosis, they are experiencing a form of pedomorphosis called neoteny.

The reasons for this neoteny, and related traits, will be examined in depth in Part III of my posts regarding Belyaev’s fox experiment.

 

An Illustration

My friend, Stefan Psarkos, made a physical model of the changes seen in Belyaev’s foxes. A photo of his model is shown below.  This model illustrates the depigmentation, floppy ears, and erect tail set that selection for tameness has been associated with.

On the left is the ‘typical’ fox, with erect ears, normal colouration and a low set tail. The fox on the right is what Belyaev got after selecting for tameness – a fox with piebaldism, an erect and curly tail, and drop ears.

 

 

References: Continue reading →

02/5/11

Belyaev’s Foxes – Introduction – Part I

ResearchBlogging.org 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: Continue reading →

01/5/11

Wolves and Domestication

Considering that dogs can breed with wolves and produce fertile offspring, they are defined as the same species. Obviously, however, there are huge differences between dogs and wolves. I am currently reading Coppinger and Coppinger’s book, Dogs: A new understanding of canine origin, behavior, and evolution (which I highly recommend), and some of the differences that they point out are:

  1. Dogs are more successful than wolves, and in fact any other canid.  There are a lot of dogs in the world, and not so many of any wild species.
  2. Dogs come in a lot of shapes and sizes. Wolves come in one.
  3. Wolves are not very adaptable – environmental changes have considerably disrupted their populations. Dogs adapt well.
  4. Wolves are not highly specialised and are, indeed, a generalised predator.  For any skill or sense, you can find a dog that can do it better than a wolf.  (e.g. Greyhound run faster than wolves, Bloodhounds smell better, etc)
  5. Wolves and dogs do not behave the same.
  6. Wolves avoid people.  Dogs live around or with humans, and indeed seek them for food.
  7. Wolves kill their own food, while dogs rarely hunt (and indeed are quite bad at it, if you consider The Trio of Dogs study I wrote about).
  8. Wolves are had to train and tame, while dogs, obviously, are biddable and tame.
  9. Dogs and wolves have different cognitive abilities. Wolves are better at problem solving, learning by imitation, and observation, while dogs learn from repetition.  Wolves do cleverer things, but dogs are more able to be conditioned to do clever things.

Clearly, there has been a big change here. Dogs are the same species as wolves (Canis lupus), but are a recognised subspecies. There has been a lot of talk about how dogs eventuated, especially considering these very pronounced differences between wolves and their subspecies.

There seems to be two arguements to how this development took place.

One suggests that humans took wolf cubs, domesticated them and, over successive generations, the wolves became more tame, the humans suggested for more dog-like characteristics, and eventually we ended up with a dog.

Another suggests that some wolves found the human camp sites to be of appeal, and chose to occupy surrounding areas. For these wolves, become less-scared of humans was advantageous (i.e. they got more food from it) and so they were more successful.

These two conflicting ideas (humans domesticating dogs, or dogs domesticating themselves) seem to speak loudly in in texts.  Indeed, Coppinger & Coppinger (pg 41) say, “Looking closely at the behaviour of wolves, and understanding the biology of a wild animal, I don’t think there is a ghost of a chance that people tamed and trained wild wolves and turned them into dogs. I think a population (at least one) of wolves domesticated themselves.”

Personally, I don’t understand why the two theories are exclusive.  Who is not to say that wolves floated around campsites and became a little more tame, and some of these wolfpups were taken in and raised by humans?  How about if wild wolf pups were taken into the camp, had strange abnormalities (not unlike what we see in domesticated dogs) that meant they were unsuccessful as a hunter, and so had to, by necessity, float around the camp?

I think this was probably a joint venture – wolves wanted to be domesticated, and humans decided to domesticate as well. And it’s not inconceivable to think that many populations of wolves and people decided to undertake this venture.

For further reading into this area, have a look at this blog (“Evolution: The Curious Case of Dogs”) and I highly recommend the Coppingers’ book.