Fox Essay

1. To what extent does
breeding for a
behavioural characteristic
affect genetic qualities in
silver foxes?
Saskia Wyville

2. 1


To what extent does breeding for a behavioural characteristic
affect genetic qualities in silver foxes?


INTRODUCTION

Apart from a few characteristics that are environment-linked, almost every aspect of
human and animal appearance can be attributed to that individuals genetics. It is rather
obvious to see where appearance and genes are linked and inherited, as when two
individuals reproduce, offspring often appear very similar to the parents. In a basic
example, if two Dalmatian breed dogs (Canis familiaris) are bred together, the resulting
pups are almost invariably going to look like the adults- white, with black spots.

The reason why this happens is because these dogs have been bred to have the same
alleles of the genes that control what the animal looks like (its phenotype). An allele is a
variation of the gene, eg. spotted coat allele and plain colour coat allele. Pedigree dog
breeds came about by people selecting which animals to breed together for the best
looking offspring over many generations. The results of this selective breeding are
hundreds of different dog breeds with different appearances, ranging from different
sizes of animal (Chihuahua and Great Dane), to different coat types (Chinese crested and
poodle), to different uses of the dog (companion dogs and herding dogs).
I


However, as well as members of the same breed often having similar physical traits, they
often have very similar behavioural traits. It is a generally accepted belief that Great
Danes are silly and will often ‘clown around’, and that a golden retriever will be a loyal
family pet. Other breed linked behaviours are often seen, such as a herding behaviour in
Border collies, or digging behaviour in terriers.
II


One reason that certain breeds seem to have behaviours associated with them could be
linked with the genetics of the breed- if an animal is bred for a certain characteristic then
there are other characteristics that may be linked to it. An example of behaviour that
shows a strong chance of being linked to genetics is tortoiseshell cats- although not
technically a breed, the genetics for colouration of a tortoiseshell are very specific, and
so is the reputation they have for being a somewhat feisty animal to handle. Another,
non-behavioural example of linked genes is shown in another coat colour of cats- white
cats with blue eyes, seemingly irrelevant of breed, often seem to suffer from partial or
full deafness.

Behaviour, however, if linked to genetics, would be a more indirect association, as what
a gene actually codes for is a string of amino acids, which then in turn create a protein.
There are many types of protein, and each one has its own function. Types of protein
called enzymes are responsible for controlling chemical reactions in the body. If a gene
controls production of an enzyme that causes pigment to be produced in the eye, for
instance, this can result in eye colour. Some behaviours could be controlled by
hormones, which are chemical signals or messengers, and so it is reasonable to assume
that if a gene controls production of a certain hormone, it can also affect and control the
behaviour caused by that hormone.

GENETIC MARKERS OF DO MESTICATION

There are certain phenotypic characteristics that occur only, or in an increased
frequency, in domesticated animals. These are shown in the table below, alongside the
domesticated species that show them.

3. 2



Table 1- The ‘characteristics of domestication’ and the species that display them
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Characteristic of Domestication
Domesticated species that display
characteristic
Dwarf and giant varieties All
Piebald coat colour/Depigmentation All
Wavy or curly hair
Sheep, dogs (poodles), donkeys, horses,
pigs, goats, mice, guinea pigs
Rolled tails Dogs, pigs
Shortened tails, fewer vertebrae Dogs, cats, sheep
Floppy ears
Dogs, cats, pigs, horses, sheep, goats,
cattle
Changes in reproductive cycle All except sheep

These characteristics were noted by Charles Darwin in his book ‘The Origin of Species’
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and they have been debated over for many years, as one of the main issues is that how
can one species of animal develop so many different characteristics only when
domesticated?

For the most part, many of these conditions are not present in wild type animals because
they would not be a desirable characteristic for a wild animal to have. Using wolves as an
example, if a wolf was born with a piebald coat colour, or a coat colouration similar to a
dalmation, it is likely that it would be unable to hunt as effectively as another wolf who
had a coat pattern that was more natural, due to the fact the coat will make it stand out
and so prevent any covert movement towards prey animals. If a wolf was born with
floppy ears, or a curled tail, it would be unable to communicate effectively with other
wolves, both in its own pack and wolves outside the pack, because ear and tail
movements are vital non-verbal methods of communication between wolves. This would
likely lead to it being unsuccessful at integrating fully into a pack, and as an animal which
hunts large game in packs, wolves can often find it difficult to survive on their own.

The qualities above then, often only appear in domesticated populations. Sometimes wild
animals do appear with these qualities, but usually only as a result of a cross between a
wild and domestic animal. For example, if a dog with such characteristics mated with a
wild wolf, then that could lead to a litter of wolves with similar characteristics. Black
wolves, it is believed, get their colour because of a cross between a wolf and a black dog
generations ago, and only because that mutation in coat colour was not particularly
unhelpful and so did not disadvantage those individuals with it, has it survived and been
passed on to the present day.

The main question that arises from these characteristics seems to be one of whether the
characteristics were born from domestication or if humans domesticated the animals
because they had desirable characteristics which made them appealing to us. Furthering
on from this, if the characteristics were caused by the domestication of the animals, at
what point in the process did they occur and why did this happen? Another is how much
variety was un-selected for, as it makes sense that getting a handful of individuals with a
rolled tail and breeding them together will lead to more like them, but without seeking
out to prefer one characteristic over another, exactly how much of the variance came
naturally?

4. 3


BACKROUND ON EXPERIMENT

The Silver Fox breeding experiment was set up at the Institute of Cytology and Genetics
in Novosibirsk, Siberia, by geneticist Dmitry K. Belyaev
V
. Belyaev’s belief in orthodox
genetics had cost him his job during the Communist regime of the USSR in the 1940’s,
and so to continue his genetic research in the 1950’s he set up the Institute with a front of
studying animal physiology.
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This was incredibly risky and it was a very real risk that if
the government looked into his work and did not like what they found, he could very
easily be arrested and become a political prisoner.
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Belyaev firmly believed that behaviour was somehow linked to genetics, and that
breeding for one particular trait would lead to genetic changes of the population of the
animals in question. He decided that he would test this hypothesis by conducting a
breeding experiment at the Institute, and for his test subjects he would use a silver
colour variant of a red fox (Vulpes vulpes).

He chose domestication as the behavioural factor to study because of the range of
animals that are already domesticated, and the great puzzle as to how we humans first
began the domestication of many of them, most specifically, the wolf (Canis lupus). For
many years, even before Darwin addressed this issue in ‘The Origin of Species’, there
have been debates about issues such as how dogs, as decedents of one species, can be
so varied between the species, and how domestication as a process took place in the first
instance- was it humans who actively instigated the process of transforming the wolf? Or
did the wolves that were least afraid of humans begin to inch closer to the camps, in
order to feed off the waste humans left behind, and then the humans began to entice
them further, eventually domesticating them?

The reasons why he chose the fox, rather than any other animal, were numerous. Firstly,
silver foxes were relatively easy to get in fairly large numbers, as there were many fur
farms in Russia that contained very many foxes for the researchers to test and choose
from as their founding population. The foxes coming from fur farms also meant that they
were already semi domesticated, as they had been bred in captivity and as such the
stresses of being kept in confinement will be reduced than if the research started with
purely wild animals.
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Secondly, foxes are very similar to dogs both physically and genetically, as they are both
members of the Canidae family. Because of this similarity, Belyaev believed that by
finding out how domestication could be conducted on the foxes, a similar scenario may
well have been presented during the domestication of the wolf. This could possibly bring
an answer to some of the questions mentioned above, and possibly provide evidence for
one or another scenario of domestication. It might even bring up a scenario previously
not thought of, but if the experiment was a success, it would certainly provide more
information for the debate to be continued on.

METHOD

The founding population of the domestication project consisted of 30 dog foxes and 100
vixens.
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Although this was an experiment in domesticating wild animals, the initial
individuals were not truly wild, as they had been selected from fur farms so were already
somewhat tamer than any wild-caught animal. The only quality the foxes are selected for
is tameness and tameness alone.
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To assess what could be considered a highly
subjective quality, a set of criteria are created that all the animals are tested by once a

5. 4


month between the ages of one and six or seven months.
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When the foxes reach sexual
maturity at about eight months, they are given a tameness score and assigned to a class.

There are three classes; Class III, which contains the least tame foxes, who typically flee
from the experimenters or bite them. Class II animals show no emotional response to the
experimenters but do allow themselves to be petted and handled. Class I foxes are
friendly and display behaviours such as wagging tails and whining. There was also an
extra category added in called Class IE, for the “domesticated elite”. These animals are
eager to establish contact with humans and go so far as to lick the experimenter’s hands,
a behaviour seen in almost any pet dog.
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After the foxes have been given a class rating, the selection is made of which ones are
bred to form the next generation. The highest scoring foxes are chosen to breed, while
the lowest scoring ones are now excluded from the breeding program. This process is
repeated for every filial generation, and has done since the program started.

One thing that does not happen at any point is selecting a fox because of its appearance.
XV XVI
If a fox is born with a curly tail, or a piebald coat, it is not chosen because of those
features to be bred forward. This is one of the most unique and critical aspects of this
experiment- by breeding purely for behaviour, all changes in appearance must be a
result of the behavioural selection, rather than selection for the appearance factors.

Each individual has its behaviour and phenotype (appearance) carefully documented, so
that over the course of the experiment, results can be formed about how each generation
differed from the one before it. There are also other measurements taken, such as the
physical properties of the foxes (skull size, body length, etc)
XVII
to enable any
comparison that is required to be made easily. Foxes that are not accepted into the
breeding group, due to being aggressive or not being one of the percentage of tame
animals that are used, are culled as they are no longer part of the experiment and as such
do not serve a useful purpose anymore.

To limit the effect of inbreeding on the experiment, there was a mating system designed
and operated throughout the experiment to keep the inbreeding level as low as possible.
The inbreeding coefficient (which gives the percentage change that a fox will receive an
identical allele from both of its parents) varies between 0.02 and 0.07- meaning the
percentage chance of a fox receiving the same allele from both its parents is between 2
and 7%, a remarkably low number.
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XIX


A control group of foxes was bred alongside the experimental group so as to ensure that
any results that may be found can be compared against a non-selected population of
foxes that experience the same conditions as the others, the only difference being that
these individuals are not selected for tameness. This is referred to as the ‘non-
domesticated’ group. This is a vital occurrence in trials as it allows valid comparisons to
be made between groups in the experiment and to ensure that the results of the
experiment are due to the chosen variable and not any outside factors.

DATA

Some data collected from the experiment about the appearance and behaviour of the
foxes over time is shown in the two tables below.

Table 1- The number and proportion of selected generations that fall under the ‘elite’
category
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6. 5



Generation of
selection
Number of
offspring scored
Elite animals
Number Proportion, %
1965 (F6) 213 4 1.8
1970 (F10) 370 66 17.8
1980 (F20) 1438 503 35.0
1990 (F30) 1641 804 49.0
2002 (F42) 902 642 71.2


Table 2- The number of foxes that have certain characteristics in the domesticated
population in 1999 compared to the non-domesticated population
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PARALLEL STUDIES

Although this experiment and its results are unique, there have been other parallel
studies conducted at the institute. As well as foxes, the researchers there also attempted
to domesticate river otters (Lutra lutra) and grey rats (Rattus norvegicus).
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XXIII

XXIV

XXV

The Institute also decided to attempt a reversal of the process of domestication, and
repeated the experiment but by breeding for aggressiveness in the foxes instead.

The aggressive fox experiment worked as well as the tame fox experiment. As a person
walks down the middle of the room with the fox cages in, the foxes bay at them and hurl
themselves at the bars in an attempt to attack the person.
XXVI
The effectiveness of this
side experiment has enabled the researchers to test another avenue of domestication-
nature versus nurture.

A way to test if the foxes behaviour is because of its genes or if the way it is brought up is
by switching a tame fox cub with an aggressive fox cub at birth, and observing how it is
classed when it grows. The researchers also went one step further and switched the
embryos of both an aggressive and tame pregnant fox so that the tame fox would give
birth to the aggressive cubs, and vice versa.
XXVII


Despite the fox cubs being raised by ‘opposite’ mothers, the results showed only slight
variance to what was expected- that is, the tame cubs grew up to be tame, and the
aggressive ones were just as aggressive as they had expected them to be. This is major
evidence supporting the evidence showing that the tame behaviour is genetically linked,
and that the foxes are actually domesticated from birth and it is not something that they
grow up to learn.

Characteristic
Animals per 100,000 with trait
Increase in
frequency, %
Domesticated
population
Non-domesticated
population
Depigmentation
(Star)
12,400 710 +1,646
Brown mottling 450 86 +423
Grey hairs 500 100 +400
Floppy ears 230 170 +35
Short tail 140 2 +6,900
Rolled tail 9,400 830 +1,033

7. 6


Another thing that the experimenters did was to create tame-aggressive hybrids, which
seemed to help fulfil the genetic basis theory as the offspring from such pairings did
seem to be classified as somewhere in between the two.

The rat experiment was also successful. Although they did not test for any major genetic
phenotype changes, the rats they managed to breed were fully domesticated and
actively sought out human contact.
XXVIII
Again they repeated the aggressive experiment,
and again it was successful, so they now have a tame and an aggressive line of rats.
Further experiments are being conducted on both strains at other research centres in an
attempt to try and discover the genetics behind aggressive and tame behaviour.
XXIX


The otter experiment did not succeed in breeding any domesticated otters, however that
does not mean that it was a failure.
XXX
Instead, this could open up a new host of enquiries
into domestication and how it differs from species to species- many questions can be
taken from this, such as if there are certain species that can be domesticated and some
that can’t, and why, or if some species are more responsive to the pressure of
domestication than others, and why. Rather than pulling this experiment to a halt, it has
opened up new lines of experimentation that some may choose to develop.

DATA ANALYSIS

The data that is present in table 1 clearly shows that more foxes over time have been
tested and placed into the ‘domesticated elite’ group. This means that the foxes’
behaviour towards the researchers has changed from each generation to the next-
moving away from the avoidance that would be shown by a class III animal, to a huge
proportion (71%) of the animals by the 42nd generation actively seeking out contact with
the people and being considered to be fully domesticated.
XXXI


This table means that, for some reason, the animals that have been bred on from the last
generation are producing litters with consistently tamer cubs. As the proportion of ‘elite’
animals increases, there are more of them breeding together and so it is reasonable to
assume that the behaviour is passed on from parent to offspring as seems to be shown by
the data available, which does suggest that as the amount of tame animals breeding
increases, the amount of tame offspring increases.

Table 2 shows us that the qualities deemed as ‘markers of domestication’ occur more
frequently in the domestic population than in the non-domesticated control population.
There is an increase in percentage frequency for every single trait named, and the
increases vary from an increase of 35% all the way up to an increase of 6,900%.
XXXII


This means that, in the domesticated population, there is a trait apparent in many of the
animals that causes the difference in genetics and the phenotype of the animals. It is
reasonable to assume that these characteristics are passed on from parent to offspring,
however because there is no information about lineage it is something that can only be
considered as a way of passage of the genetic information.

One concern about these trends is that it is a result of inbreeding, and so artificially
increasing the frequency of the gene alleles that the foxes have. This concern is largely
unfounded because as mentioned elsewhere in this report, inbreeding has been
carefully monitored and kept to very low levels to avoid this situation occuring.

8. 7


CONCLUSION

Looking at the data collected from this experiment, it is possible to conclude that
breeding for tameness as a behavioural characteristic does affect the genetic qualities in
silver foxes.

This can be said because there is a clear link between the foxes bred to be
domesticated, and the phenotype that they express. This link is clear because when
compared to the non-domesticated control population, there is a significant increase in
the number of animals that exhibit the factors deemed to be the most important signifiers
of a link to domestication.

As mentioned earlier, at no point were the animals chosen based on their appearance.
The sole factor in determining which foxes would go on to breed to the next generation
was how tame they were- the tamest ones bred while the others were excluded from
further breeding.
XXXIII
This means that human influences on deciding which appearance
characteristics were the most desirable were non-existent, and so the cause must have
been linked to the domesticated behaviour of the animals.

There is also a clear increase in the number of animals that are graded into the ‘elite’
group when they are tested for tameness in the later generations than in the earlier ones.

This could possibly be due to the foxes being born into an environment where they are
exposed to interactions with humans and that this has caused them to grow up tame. The
flaw here is the control group- to make the observations valid, the control group was
bred alongside the experimental group, and so was exposed to everything they were-
they received the same food, same interaction and same environment as each other, the
only difference being if they were selected to be tame or not. This removes any
environmental factor as causing what is a dramatic change in a population’s behaviour.

Although the characteristics selected were limited to phenotype and outward
appearance only, other factors could also have been considered. Genes code for
proteins, and so altering the genes could have altered how much of a particular protein
was produced, and in this way it affected the animal’s phenotype.

More information on what caused the behaviour of the foxes to alter over the course of
the experiment could also have been used to give further information about how the
genetics of behaviour work, and how exactly tame behaviour is achieved in the foxes. If
it is down to production of particular hormones that affect behaviour, the levels of these
hormones could be recorded and give further insight into how behavioural genetics is
affected by breeding for tameness.

WHAT NEXT

The results from this experiment may have many extensive, far reaching consequences.
As mentioned above with the parallel experiments that have also being carried out, the
results from those suggest further research could be carried out to determine how
domestication affects different animal species, and if indeed some animals are simply
unable to be domesticated, exactly why this occurs.

If domestication really is, as this experiment strongly suggests, tied very closely with
genetics, it may be possible to locate the gene or genes responsible for the behaviour
that these foxes display. If these genes could be isolated then further research could be

9. 8


done to discover if the presence or lack of these genes is in any way related to how well
or how easily certain animals can be domesticated.

The fox experiment also could provide evidence and answers for issues regarding the
development of humans. Many theories exist as to why humankind developed as it did-
why some primates descended from the trees and began to walk on two legs and
develop into what would eventually become humans, whilst others remained primarily
arboreal or even if they did transfer their lives to the ground, why they have not
developed as humans did.

Many believe that humans underwent a form of self-domestication, much like a theory
relating to how wolves became domesticated. If this is indeed the case, and humans
placed their own domestic pressures onto themselves, then it could mean that over
thousands of years of human development we may have been unconsciously selecting
for those with the ‘tamest’ traits, who would actively seek to become integrated within a
group and actively socialise together. Primates are often quite social animals, with many
modern-day species living in large social groups, which, if true for human ancestors,
would have helped in this selection process.

There are further reasons why this experiment could relate to early human development,
such as accounting for the great variability that exists between people from different
areas of the world, or even within one localised population. Although it is known why
humans have their defining features (for instance, a paler skin tone due to a lower
melanin content eases the synthesis of vitamin D from the Sun in northern temperate and
arctic areas, where the Sun’s light is not as strong as in tropical, equatorial regions- the
areas that humans are known to have first developed), the biological and genetic
changes that may have been caused by humans self-selecting for domestication on
behaviour could have enabled such a wide variation in phenotype to develop within the
human species.

These are just my own speculations and possible ideas that have come up in discussion
with other people on this topic, but it is clear that this information in the hands of the right
people with the right facilities available to them could be used to answer just some of the
thousands of unanswered questions there are about how humans, as well as other
animals, evolved and developed over the thousands of years that many have walked the
earth.

FINAL THOUGHTS

This experiment has been progressing since it was first set up in 1959, under the
direction of Belyaev himself until his death in 1985; then under the care of Lyudmila Trut
until the present day. Over the past 5 decades, the institute has grown to accommodate
world-class research into both classical and molecular genetics, particularly under the
guidance of Belyaev. Belyaev’s work on evolution is ground-breaking, and animal
domestication was his lifelong project.
XXXIV


Throughout these decades, the project has continued to flourish, surviving intact through
the troubles of the Cold War and the breakdown of the USSR in 1991. Unfortunately, due
to Russia’s economic problems in the late 1990’s the project was in serious danger of
having to be halted. In 1996, there were 700 breeding animals at the center. In 1998, due
to serious cutbacks and withdrawal of outside grants necessary to maintain this
experiment, the number of foxes was cut to just 100.
XXXV
As of 2010, the project is still

10. 9


functioning; however I was unable to find any information about how the scale had
altered since the cuts of 1998.

Previously, the Institute could gather extra funds by selling the pelts of the foxes that
were culled from the breeding herd. Possibly due to animal rights campaigners and the
increase in use of fake fur, this source of income has vanished. Although the people at the
Institute are working hard to find innovative new ways to draw in money, it is difficult.
Some of the current methods include selling some of the foxes to Scandinavian fur
breeders, under pressure from animal rights groups to use animals that were not
suffering under the captive conditions present on a fur farm.
XXXVI


One other method is particularly entrepreneurial- selling the foxes that are not used in
the breeding program as pets. Anyone can inquire to the Institute directly via email to
request information regarding buying one as a pet, as well as there being some
specialist companies set up to distribute the foxes.
XXXVII

XXXVIII
These animals are typically
adopted out at around 4 months of age and all are neutered to prevent owners breeding
from them.
XXXIX
Although questions could be raised as to the suitability of these animals
as household pets- experiences from the researchers themselves keeping some animals
as pets seem to suggest that the foxes adapt well to living in a home environment, even
so far as becoming house trained and learning basic training commands.
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Of course, the main method of creating revenue will be through grants and funding from
organisations and governments. However due to the current economic situation
worldwide, it is entirely plausible that funding may be cut to not just this scientific
research development, but to others in general.

This would be a catastrophic loss because if this project is able to continue and develop
far more than it already is, there is no telling exactly what could be discovered from the
research conducted here, or what sort of animal these domestic foxes may yet become.

11. 10


BIBLIOGRAPHY

Trut, L. N. (1999) Early Canid Domestication: The Farm-Fox Experiment, American
Scientist 87, pp 160-169

Kukekova, A. V. et al (2006) The genetics of Domesticated Behaviour in Canids: What can
Dogs and Silver Foxes Tell Us about Each Other? Chapter 26. The Dog and Its Genome.
Cold Spring Harbour Laboratory Press, Woodbury, pp 515-537

Trut, L. N. et al (2004) An Experiment on Fox Domestication and Debatable Issues of
Evolution of the Dog, Russian Journal of Genetics 40, no 6. pp 644-655. Translated from
Genetika 40, no. 6, (2004) pp 794-807

Trut, L. N. et al (2009) Animal evolution during domestication: the domesticated fox as a
model, BioEssays 31, pp 349-360

Kukekova, A. V. et al (2008) Measurement of Segregating Behaviours in Experimental
Silver Fox Pedigrees, Behaviour Genetics 38, pp 185-194

Browne, M. W. (1999) New Breed of Fox as Tame as a Pussycat, New York Times

Wade, N. (2006) Nice Rats, Nasty Rats: Maybe It’s All in the Genes, New York Times

Ratliff, E. (2011) Taming the Wild, National Geographic

Trut, L. N. (2006) Morphology and Behaviour: Are They Coupled at the Genome Level?
Chapter 6. The Dog and Its Genome. Cold Spring Harbour Laboratory Press, Woodbury,
pp 81-93

Adams, J. (2008) Genetics of Dog Breeding, Nature Education

Darwin, C. (1872) The Origin of Species, Sixth Edition, Greycaine Limited, Watford, pp
34-63

BBC Horizon, Secret Life of the Dog, 2010

Laboratory of Evolutionary Genetics of Animals, Institute of Cytology and Genetics,
Russia
http://www.bionet.nsc.ru/booklet/Engl/EnglLabaratories/LabEvolutionaryGeneticsAnim
alsEngl.html

Silver Fox Distribution USA
http://www.sibfox.com/

Study of the Molecular Basis of Tame and Aggressive Behaviour in the Silver Fox Model
http://cbsu.tc.cornell.edu/ccgr/behaviour/Index.htm

Biological Bases of Behaviour of Domestic Dog Breeds
http://www.ao.net/~holmanh/CoppBioBases/CoppBioBases.htm

The Behavioural Genetics of Dogs
http://www.animalbehavioronline.com/dogbehavioralgenetics.html

12. 11




I
Adams, J. (2008) Genetics of Dog Breeding, Nature Education

II
Adams, J. (2008) Genetics of Dog Breeding, Nature Education

III
Trut, L. N. (1999) Early Canid Domestication: The Farm-Fox Experiment, American Scientist 87, pp 160-169

IV
Darwin, C. (1872) The Origin of Species, Sixth Edition, Greycaine Limited, Watford, pp 34-63

V
Trut, L. N. (1999) Early Canid Domestication: The Farm-Fox Experiment, American Scientist 87, pp 160-169

VI
Trut, L. N. (1999) Early Canid Domestication: The Farm-Fox Experiment, American Scientist 87, pp 160-169

VII
Ratliff, E. (2011) Taming the Wild, National Geographic

VIII
Trut, L. N. (1999) Early Canid Domestication: The Farm-Fox Experiment, American Scientist 87, pp 160-169

IX
Trut, L. N. et al (2009) Animal evolution during domestication: the domesticated fox as a model, BioEssays
31, pp 349-360

X
Trut, L. N. (1999) Early Canid Domestication: The Farm-Fox Experiment, American Scientist 87, pp 160-169

V
Trut, L. N. (1999) Early Canid Domestication: The Farm-Fox Experiment, American Scientist 87, pp 160-169

XII
Trut, L. N. et al (2009) Animal evolution during domestication: the domesticated fox as a model, BioEssays
31, pp 349-360

XIII
Trut, L. N. et al (2009) Animal evolution during domestication: the domesticated fox as a model, BioEssays
31, pp 349-360

XIV
Trut, L. N. (1999) Early Canid Domestication: The Farm-Fox Experiment, American Scientist 87, pp 160-169

XV
Trut, L. N. (1999) Early Canid Domestication: The Farm-Fox Experiment, American Scientist 87, pp 160-169

XVI
Trut, L. N. et al (2009) Animal evolution during domestication: the domesticated fox as a model, BioEssays
31, pp 349-360

XVII
Trut, L. N. (2006) Morphology and Behaviour: Are They Coupled at the Genome Level? Chapter 6. The
Dog and Its Genome. Cold Spring Harbour Laboratory Press, Woodbury, pp 81-93

XVIII
Trut, L. N. (1999) Early Canid Domestication: The Farm-Fox Experiment, American Scientist 87, pp 160-
169

XIX
Trut, L. N. et al (2004) An Experiment on Fox Domestication and Debatable Issues of Evolution of the Dog,
Russian Journal of Genetics 40, no 6. pp 644-655. Translated from Genetika 40, no. 6, (2004) pp 794-807

XX
Trut, L. N. et al (2004) An Experiment on Fox Domestication and Debatable Issues of Evolution of the Dog,
Russian Journal of Genetics 40, no 6. pp 644-655. Translated from Genetika 40, no. 6, (2004) pp 794-807

XXI
Trut, L. N. (1999) Early Canid Domestication: The Farm-Fox Experiment, American Scientist 87, pp 160-169

XXII
Trut, L. N. (1999) Early Canid Domestication: The Farm-Fox Experiment, American Scientist 87, pp 160-169

XXIII
Adams, J. (2008) Genetics of Dog Breeding, Nature Education

XXIV
Ratliff, E. (2011) Taming the Wild, National Geographic

XXV
Wade, N. (2006) Nice Rats, Nasty Rats: Maybe It’s All in the Genes, New York Times

XXVI
BBC Horizon, Secret Life of the Dog, 2010

XXVII
Trut, L. N. (1999) Early Canid Domestication: The Farm-Fox Experiment, American Scientist 87, pp 160-
169

XXVIII
Wade, N. (2006) Nice Rats, Nasty Rats: Maybe It’s All in the Genes, New York Times

13. 12





XXIX
Wade, N. (2006) Nice Rats, Nasty Rats: Maybe It’s All in the Genes, New York Times

XXX
Trut, L. N. (1999) Early Canid Domestication: The Farm-Fox Experiment, American Scientist 87, pp 160-169

XXXI
Trut, L. N. et al (2004) An Experiment on Fox Domestication and Debatable Issues of Evolution of the Dog,
Russian Journal of Genetics 40, no 6. pp 644-655. Translated from Genetika 40, no. 6, (2004) pp 794-807

XXXII
Trut, L. N. (1999) Early Canid Domestication: The Farm-Fox Experiment, American Scientist 87, pp 160-
169

XXXIII
Trut, L. N. (1999) Early Canid Domestication: The Farm-Fox Experiment, American Scientist 87, pp 160-
169

XXXIV
Trut, L. N. (1999) Early Canid Domestication: The Farm-Fox Experiment, American Scientist 87, pp 160-
169

XXXV
Trut, L. N. (1999) Early Canid Domestication: The Farm-Fox Experiment, American Scientist 87, pp 160-
169

XXXVI
Browne, M. W. (1999) New Breed of Fox as Tame as a Pussycat, New York Times

XXXVII
Laboratory of Evolutionary Genetics of Animals, Institute of Cytology and Genetics, Russia
http://www.bionet.nsc.ru/booklet/Engl/EnglLabaratories/LabEvolutionaryGeneticsAnimalsEngl.html

XXXVIII
Silver Fox Distribution USA
http://www.sibfox.com/

XXXIX
Silver Fox Distribution USA
http://www.sibfox.com/

XL
Ratliff, E. (2011) Taming the Wild, National Geographic