Dog
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This article is about the domestic dog. For other uses, see Dog
(disambiguation).
Domestic dog
Fossil range: Late Pleistocene – Recent
A Labrador Retriever
Conservation status
Domesticated
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Canidae
Genus: Canis
Species: C. lupus
Subspecies: C. l. familiaris
Trinomial name
Canis lupus familiaris
(Linnaeus, 1758)
Synonyms
These are INVALID scientific names for historical interest only:
aegyptius (Linnaeus, 1758), alco (C. E. H. Smith, 1839), americanus
(Gmelin, 1792), anglicus (Gmelin, 1792), antarcticus (Gmelin,
1792), aprinus (Gmelin, 1792), aquaticus (Linnaeus, 1758), aquatilis
(Gmelin, 1792), avicularis (Gmelin, 1792), borealis (C. E. H.
Smith, 1839), brevipilis (Gmelin, 1792), cursorius (Gmelin, 1792),
domesticus (Linnaeus, 1758), extrarius (Gmelin, 1792), ferus (C.
E. H. Smith, 1839), fricator (Gmelin, 1792), fricatrix (Linnaeus,
1758), fuillus (Gmelin, 1792), gallicus (Gmelin, 1792), glaucus
(C. E. H. Smith, 1839), graius (Linnaeus, 1758), grajus (Gmelin,
1792), hagenbecki (Krumbiegel, 1950), haitensis (C. E. H. Smith,
1839), hibernicus (Gmelin, 1792), hirsutus (Gmelin, 1792), hybridus
(Gmelin, 1792), islandicus (Gmelin, 1792), italicus (Gmelin, 1792),
laniarius (Gmelin, 1792), leoninus (Gmelin, 1792), leporarius
(C. E. H. Smith, 1839), major (Gmelin, 1792),mastinus (Linnaeus,
1758), melitacus (Gmelin, 1792), melitaeus (Linnaeus, 1758), minor
(Gmelin, 1792), molossus (Gmelin, 1792), mustelinus (Linnaeus,
1758), obesus (Gmelin, 1792), orientalis (Gmelin, 1792), pacificus
(C. E. H. Smith, 1839), plancus (Gmelin, 1792), pomeranus (Gmelin,
1792), sagaces (C. E. H. Smith, 1839), sanguinarius (C. E. H.
Smith, 1839), sagax (Linnaeus, 1758), scoticus (Gmelin, 1792),
sibiricus (Gmelin, 1792), suillus( C. E. H. Smith, 1839), terraenovae
(C. E. H. Smith, 1839), terrarius (C. E. H. Smith, 1839), turcicus
(Gmelin, 1792), urcani (C. E. H. Smith, 1839), variegatus (Gmelin,
1792), venaticus Gmelin, 1792), vertegus (Gmelin, 1792)[1]
The dog (Canis lupus familiaris)[2] is a domesticated subspecies
of the wolf, a mammal of the Canidae family of the order Carnivora.
The term encompasses both feral and pet varieties and is also
sometimes used to describe wild canids of other subspecies or
species. The domestic dog has been one of the most widely kept
working and companion animals in human history, as well as being
a food source in some cultures. There are estimated to be 400
million dogs in the world.[3]
The dog has developed into hundreds of varied breeds.
Height measured to the withers ranges from a few inches in the
Chihuahua to a few feet in the Irish Wolfhound; color varies from
white through grays (usually called blue) to black, and browns
from light (tan) to dark ("red" or "chocolate")
in a wide variation of patterns; and, coats can be very short
to many centimeters long, from coarse hair to something akin to
wool, straight or curly, or smooth.[4]
Contents [hide]
1 Etymology and related terminology
2 Taxonomy
3 Origin and evolution
3.1 Origins
3.2 Ancestry and history of domestication
3.3 Development of dog breeds
3.3.1 Breed popularity
4 Physical characteristics
4.1 Differences from other canids
4.2 Sight
4.3 Hearing
4.4 Smell
4.5 Coat color
4.6 Tail
4.7 Sprint metabolism
5 Behavior and intelligence
5.1 Differences from other canids
5.2 Intelligence
5.2.1 Evaluation of a dog's intelligence
5.3 Human relationships
5.4 Dog communication
6 Reproduction
6.1 Differences from other canids
6.2 Life cycle
6.3 Spaying and neutering
6.4 Overpopulation
6.4.1 United States
7 Working, utility and assistance dogs
8 Show and sport (competition) dogs
9 Dog health
9.1 Morbidity (illness)
9.1.1 Diseases
9.1.2 Parasites
9.1.3 Common physical disorders
9.2 Mortality (lifespan and causes of death)
9.2.1 Predation
9.3 Diet
9.3.1 Nutrition
9.3.2 Dangerous substances
9.4 Dog abuse
10 Dog meat for human consumption
11 Dogs in religion
12 See also
13 References
14 Further reading
15 External links
Etymology and related terminology
The English word dog can be traced back to the Old English docga,
a "powerful breed of canine".[5] The term may derive
from Proto-Germanic *dukkon, represented in Old English finger-docce
("finger-muscle").[6] Due to the linguistically archaic
structure of the word, the term dog may ultimately derive from
the earliest layer of Proto-Indo-European vocabulary, reflecting
the role of the dog as the earliest domesticated animal.[7]
The English word hound is cognate to other Germanic
terms, including German Hund, Dutch hond, common Scandinavian
hund, Icelandic hundur which, though referring to a specific breed
group in English, means "dog" in general in the other
Germanic languages. Hound itself is derived from the Proto-Indo-European
*kwon-, which is also the direct root of the Greek ???? (kuon)
and the indirect root of the Latin canis through the variant form
*kani-.[8]
In breeding circles, a male canine is referred
to as a dog, while a female canine is called a bitch. The father
of a litter is called the sire, and the mother of a litter is
called the dam. Offspring are generally called pups or puppies
until they are about a year old. A group of offspring is a litter.
The process of birth is whelping. Many terms are used for dogs
that are not purebred.[9]
Taxonomy
The English word dog, in common usage, refers to the domestic
pet dog, Canis lupus familiaris. The species was originally classified
as Canis familiaris and Canis familiarus domesticus by Linnaeus
in 1758.[10] In 1993, dogs were reclassified as a subspecies of
the gray wolf, Canis lupus, by the Smithsonian Institution and
the American Society of Mammalogists. "Dog" is sometimes
used to refer collectively to any mammal belonging to the family
Canidae (as in "the dog family"), such as wolves, foxes,
and coyotes. Some members of the family have "dog" in
their common names, such as the Raccoon Dog and the African Wild
Dog. A few animals have "dog" in their common names
but are not canids, such as the prairie dog.
Origin and evolution
Origins
Main article: Origin of the domestic dog
Based on DNA evidence, the wolf ancestors of modern dogs diverged
from other wolves about 100,000 years ago,[11][12] and dogs were
domesticated from those wolf ancestors about 15,000 years ago.[13]
This date would make dogs the first species to be domesticated
by humans.
Evidence suggests that dogs were first domesticated
in East Asia, possibly China,[14] and some of the peoples who
entered North America took dogs with them from Asia.[14]
As humans migrated around the planet, a variety
of dog forms migrated with them. The agricultural revolution and
subsequent urban revolution led to an increase in the dog population
and a demand for specialization. These circumstances would provide
the opportunity for selective breeding to create specialized working
dogs and pets.
Ancestry and history of domestication
Main article: Origin of the domestic dog
This ancient mosaic, likely Roman, shows a large dog with a collar
hunting a lion.Molecular systematics indicate that the domestic
dog (Canis lupus familiaris) descends from one or more populations
of wild wolves (Canis lupus). As reflected in the nomenclature,
dogs are descended from the wolf and are able to interbreed with
wolves.
The relationship between human and canine has deep
roots. Converging archaeological and genetic evidence indicate
a time of domestication in the late Upper Paleolithic close to
the Pleistocene/Holocene boundary, between 17,000 and 14,000 years
ago. Fossil bone morphologies and genetic analysis of current
and ancient dog and wolf populations have not yet been able to
conclusively determine whether all dogs descend from a single
domestication event, or whether dogs were domesticated independently
in more than one location. Domesticated dogs may have interbred
with local populations of wild wolves on several occasions (a
process known in genetics as introgression).
The earliest dog fossils, two crania from Russia
and a mandible from Germany, date from 13,000 to 17,000 years
ago. Their likely ancestor is the large northern Holarctic wolf,
Canis lupus lupus. Remains of smaller dogs from Mesolithic (Natufian)
cave deposits in the Middle East, dated to around 12,000 years
ago, have been interpreted as descendants of a lighter Southwest
Asian wolf, Canis lupus Arabs. Rock art and skeletal remains indicate
that by 14,000 years ago, dogs were present from North Africa
across Eurasia to North America. Dog burials at the Mesolithic
cemetery of Svaerdborg in Denmark suggest that in ancient Europe
dogs were valued companions.
Dogs on the Coat of Arms of the Canary Islands, which in ancient
times had a dense population of an endemic breed of large and
fierce dogs.Genetic analyses have so far yielded divergent results.
Vilà, Savolainen, and colleagues (1997) concluded that
the ancestors of dogs split off from other wolves between 75,000
and 135,000 years ago, while a subsequent analysis by Savolainen
et al. (2002) indicated a "common origin from a single gene
pool for all dog populations" between 40,000 and 15,000 years
ago in East Asia. Verginelli et al. (2005), however, suggest both
sets of dates must be reevaluated in light of recent findings
showing that poorly calibrated molecular clocks have systematically
overestimated the age of geologically recent events. On balance,
and in agreement with the archaeological evidence, 15,000 years
ago is the most likely time for the wolf-dog divergence.[15]
The Soviets have attempted to domesticate the fox,
mentioned in the article Tame Silver Fox, and were able to do
so in just nine generations, or less than a human lifetime. This
also resulted in other changes, including color, which became
black, white, or black and white. They also developed year-round
breeding ability, curled-up tails, and droopy ears.
The rapidity of this change has suggested to researchers
a scenario of the origin of the domestic dog. Primitive people
lived on the edge of survival which involved occasional food shortages,
and would not have taken wolf pups and made pets of them. However,
wolves would raid garbage dumps near human habitations. Wolves
have a flight distance which they keep between themselves and
a threatening creature. When a dump was approached by humans,
some wolves would run a greater distance from the dump than others.
Those that ran the shortest distance would return first, and obtain
the greatest amount of food.
This set up a selective breeding situation that
resulted in a strain of wolves having shorter and shorter flight
distances, until they were eventually comfortable near humans,
having domesticated themselves, so to speak. At that point, they
were tolerated by humans, so long as they were also useful, in
such ways as catching rats or driving away other predators. In
time, other uses, such as hunting, were found for them. The Farm
Fox Experiment Evolution of Dogs
Development of dog breeds
Main article: Dog breeds
Dogs have been bred into a variety of shapes, colors and sizes.
Variation can be wide even within a breed, as with these Cavalier
King Charles Spaniels.There are numerous dog breeds, with over
800 being recognized by various kennel clubs worldwide. Many dogs,
especially outside the United States of America and Western Europe,
belong to no recognized breed. A few basic breed types have evolved
gradually during the domesticated dog's relationship with humans
over the last 10,000 or more years, but all modern breeds are
of relatively recent derivation. Many of these are the product
of a deliberate process of artificial selection. Because of this,
some breeds are highly specialized, and there is extraordinary
morphological diversity across different breeds. Despite these
differences, dogs are able to distinguish dogs from other kinds
of animal.
The definition of a dog breed is a matter of some
controversy. Depending on the size of the original founding population,
closed gene pool breeds can have problems with inbreeding, specifically
due to the founder effect. Dog breeders are increasingly aware
of the importance of population genetics and of maintaining diverse
gene pools. Health testing and new DNA tests can help avoid problems,
by providing a replacement for natural selection. Without selection,
inbreeding and closed gene pools can increase the risk of severe
health or behavioral problems. Some organizations define a breed
more loosely, such that an individual may be considered of one
breed as long as 75% of its parentage is of that breed. These
considerations affect both pets and the show dogs entered in dog
shows. Even prize-winning purebred dogs sometimes possess crippling
genetic defects due to founder effect or inbreeding.[16] These
problems are not limited to purebred dogs and can affect cross-breed
populations.[17] The behavior and appearance of a dog of a particular
breed can be predicted to a degree, while mixed-breed dogs show
a broader range of innovative appearance and behavior.
This puppy is a mix of many breeds.Mixed-breed dogs or Mongrels
(also called "mutts") are dogs that do not belong to
specific breeds, being mixtures more than two in variant percentages.
Mixed breed dogs and purebred dogs are both suitable as companions,
pets, working dogs, or competitors in dog sports. Sometimes different
breed dogs are deliberately bred, to create cross-breeds such
as the Cockapoo, a mixture of Cocker Spaniel and Miniature Poodle.
Such deliberate crosses may display some degree of hybrid vigor
and other desirable traits, but may or may not inherit any of
the desired traits of their parents, such as temperament or a
particular color or coat. Without genetic testing of the parents,
the crosses can end up inheriting genetic defects that occur in
both parental breeds.
A breed is a group of animals that possesses a
set of inherited characteristics that distinguishes it from other
animals within the same species. Deliberately crossing two or
more breeds is also a manner of establishing new breeds, but it
is only a breed when offspring will reliably demonstrate that
particular set of characteristics and qualities.
The Bulldog is well known for its short muzzle and saggy skin
on its face
Breed popularity
Breed popularity varies widely over time[18] and in different
parts of the world and different segments of the population. Counting
by American Kennel Club (AKC) registration (not by licensing registration
or by United Kennel Club (UKC) registration, which could present
different statistics), the Labrador Retriever has been the United
States's most commonly registered breed of dog since 1991.[19]
However, even within parts of the United States, popularity varies;
for example, in 2005 the most-registered breed in New York City
was the Poodle while the Yorkshire Terrier was the second-most-registered
breed in Houston.[20] However, animal shelters in many parts of
the United States report that the most-commonly available dog
for adoption is the American Pit Bull Terrier or pit bull-type
mixes, making up as much as 20% of dogs available for adoption,
none of which would be registered with the AKC.[21] Two decades
ago, in 1983, the AKC's top two registered breeds were the American
Cocker Spaniel and the Poodle.[22]
In the United Kingdom, The Kennel Club reports
that the most-registered breed from at least 1999 to 2005 was
the Labrador Retriever. It rounds out the top three for 1999 to
2005 with the German Shepherd Dog, also popular in the US, and
the English Cocker Spaniel[23] , which is no longer in the top
ten in the US. In the UK, a national dog adoption and rescue service
indicates that the most common breed appearing in shelters is
the Greyhound followed by the Staffordshire Bull Terrier. [24]
Physical characteristics
Main article: Dog anatomy
See also: Dog health
Comparative drawing of dog and wolf anatomy by Ernest Thompson
Seton. Note the proportionately smaller head of the dogModern
dog breeds show more variation in size, appearance, and behavior
than any other domestic animal. Within the range of extremes,
dogs generally share attributes with their wild ancestors, the
wolves. Dogs are predators and scavengers, possessing sharp teeth
and strong jaws for attacking, holding, and tearing their food.
Although selective breeding has changed the appearance of many
breeds, all dogs retain basic traits from their distant ancestors.
Like many other predatory mammals, the dog has powerful muscles,
fused wristbones, a cardiovascular system that supports both sprinting
and endurance, and teeth for catching and tearing. Unlike humans
which are plantigrade, dogs are digitigrade.
Differences from other canids
Compared to equally sized wolves, dogs tend to have 20% smaller
skulls and 10% smaller brains, as well as proportionately smaller
teeth than other canid species.[3] Dogs require fewer calories
to function than wolves. Their diet of human refuse in antiquity
made the large brains and jaw muscles needed for hunting unnecessary.
It is thought by certain experts that the dog's limp ears are
a result of atrophy of the jaw muscles.[3] The skin of domestic
dogs tends to be thicker than that of wolves, with some Inuit
tribes favouring the former for use as clothing due to its greater
resistance to wear and tear in harsh weather.[3] Unlike wolves,
but like coyotes, domestic dogs have sweat glands on their paw
pads.[3] The paws of a dog are half the size of those of a wolf,
and their tails tend to curl upwards, another trait not found
in wolves.[25]
Sight
A Greyhound, one of many breeds of sighthoundLike most mammals,
dogs are dichromats and have color vision equivalent to red-green
color blindness in humans.[26][27][28]
Different breeds of dogs have different eye shapes
and dimensions, and they also have different retina configurations.[29]
Dogs with long noses have a "visual streak" which runs
across the width of the retina and gives them a very wide field
of excellent vision, while those with short noses have an "area
centralis" — a central patch with up to three times
the density of nerve endings as the visual streak — giving
them detailed sight much more like a human's.
Some breeds, particularly the sighthounds, have
a field of vision up to 270° (compared to 180° for humans),
although broad-headed breeds with short noses have a much narrower
field of vision, as low as 180°.[26][27]
Hearing
Dogs detect sounds as low as the 16 to 20 Hz frequency range (compared
to 20 to 70 Hz for humans) and above 45 kHz[30] (compared to 13
to 20 kHz for humans),[27] and in addition have a degree of ear
mobility that helps them to rapidly pinpoint the exact location
of a sound. Eighteen or more muscles can tilt, rotate and raise
or lower a dog's ear. Additionally, a dog can identify a sound's
location much faster than a human can, as well as hear sounds
up to four times the distance that humans are able to. Those with
more natural ear shapes, like those of wild canids like the fox,
generally hear better than those with the floppier ears of many
domesticated species.
Smell
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Scent hounds, especially the Bloodhound, are iconic for their
keen sense of smell.[citation needed]Dogs have nearly 220 million
smell-sensitive cells over an area about the size of a pocket
handkerchief (compared to 5 million over an area the size of a
postage stamp for humans). Some breeds have been selectively bred
for excellence in detecting scents, even compared to their canine
brethren. What information a dog actually detects when he is scenting
is not perfectly understood; although once a matter of debate,
it now seems to be well established that dogs can distinguish
two different types of scents: an air scent from some person or
thing that has recently passed by, and a ground scent that remains
detectable for a much longer period. The characteristics and behavior
of these two types of scent trail would seem, after some thought,
to be quite different, the air scent being intermittent but perhaps
less obscured by competing scents, whereas the ground scent would
be relatively permanent with respect to careful and repetitive
search by the dog, but would seem to be much more contaminated
with other scents. In any event, it is established by those who
train tracking dogs that it is impossible to teach the dog how
to track any better than it does naturally; the object instead
is to motivate it properly, and teach it to maintain focus on
a single track and ignore any others that might otherwise seem
of greater interest to an untrained dog. An intensive search for
a scent, for instance searching a ship for contraband, can actually
be very fatiguing for a dog, and the dog must be motivated to
continue this hard work for a long period of time.
Coat color
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Domestic dogs often display the remnants of counter-shading,
a common natural camouflage pattern. The general theory of countershading
is that an animal that is lit from above will appear lighter on
its upper half and darker on its lower half where it will usually
be in its own shade. This is a pattern that predators can learn
to watch for. A countershaded animal will have dark coloring on
its upper surfaces and light coloring below. This reduces the
general visibility of the animal. One reminder of this pattern
is that many breeds will have the occasional "blaze",
stripe, or "star" of white fur on their chest or undersides.
Tail
There are many different shapes for dog tails: straight, straight
up, sickle, curled, cork-screw. In some breeds, the tail is traditionally
docked to avoid injuries (especially for hunting dogs). It can
happen that some puppies are born with a short tail or no tail
in some breeds.[31]
Sprint metabolism
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Dogs can generate large amounts of energy for a
short period of time. A dog's heart and lungs are oversized relative
to its body and its normal everyday needs. A dog also has relatively
more red blood cells than a human. Most of the time the dog will
keep the extra red blood cells stored in its spleen. When the
animal enters into a situation where its full metabolism is required,
such as play, catching game, or fighting other dogs, the extra
cells are released into the bloodstream. The "oversized"
heart and lungs will now be running at full capacity, and the
animal will have an enhanced ability to engage in aerobic activity.
This activity will produce internal heating. Dogs, being covered
in fur, are limited in their ability to cool down. After a short
time the animal must either cease its athletic activity or risk
harming itself from overheating. One can easily observe this pattern
of intense activity followed by rest periods in puppies. During
the rest phase the spleen collects red blood cells and the animal
may pant to cool down.
Behavior and intelligence
Further information: Category:Dog training and behavior
Many dogs, such as this American Water Spaniel, have had their
natural hunting instincts suppressed or altered to suit human
needs.
Many dogs can be trained to skillfully perform tasks not natural
to canines, such as in this dog agility competition.Dogs are very
social animals, but their personality and behavior vary with breed
as well as how they are treated by their owners and others who
come in contact with them. It is not uncommon for dogs to attack
humans and other animals; however, this is usually because of
lack of care or improper upbringing by its owner.
Differences from other canids
Dogs tend to be poorer than wolves and coyotes at observational
learning, being more responsive to instrumental conditioning.[3]
Feral dogs show little of the complex social structure or dominance
hierarchy present in wolf packs. For dogs, other members of their
kind are of no help in locating food items, and are more like
competitors.[3] Feral dogs are primarily scavengers, with studies
showing that unlike their wild cousins, they are poor ungulate
hunters, having little impact on wildlife populations where they
are sympatric. Free ranging pet dogs however are more prone to
predatory behaviour toward wild animals. Feral dogs have been
reported to be effective hunters of reptiles in the Galapagos
islands.[32]
Intelligence
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Main article: Dog intelligence
Dogs are valued for their intelligence. This intelligence is expressed
differently with different breeds and individuals, however. For
example, Border Collies are noted for their ability to learn commands,
while other breeds may not be so motivated towards obedience,
but instead show their cleverness in devising ways to steal food
or escape from a yard. Being highly adaptable animals themselves,
dogs have learned to do many jobs as required by humans over the
generations. Dogs are employed in various roles across the globe,
proving invaluable assets in areas such as search-and-rescue;
law enforcement (including attack dogs, sniffer dogs and tracking
dogs); guards for livestock, people or property; herding; Arctic
exploration sled-pullers; guiding the blind and acting as a pair
of ears for the deaf; assisting with hunting, and a great many
other roles which they may be trained to assume. Most dogs rarely
have to deal with complex tasks and are unlikely to learn relatively
complicated activities (such as opening doors) unaided. Some dogs
(such as guide dogs for the visually impaired) are specially trained
to recognize and avoid dangerous situations.
Evaluation of a dog's intelligence
The meaning of "intelligence" in general, not only in
reference to dogs, is hard to define. Some tests measure problem-solving
abilities and others test the ability to learn in comparison to
others of the same age. Defining it for dogs is just as difficult.
It is likely that dogs do not have the ability to premeditate
an action to solve a problem.
A mirror test is one possible measure of self-awareness.For example,
the ability to learn quickly could be a sign of intelligence.
Conversely it could be interpreted as a sign of a desire to please.
In contrast, some dogs who do not learn very quickly may have
other talents. An example is breeds that are not particularly
interested in pleasing their owners, such as Siberian Huskies.
Huskies are often fascinated with the myriad of possibilities
for escaping from yards, catching small animals, and often figuring
out on their own numerous inventive ways of doing both.
Assistance dogs are also required to be obedient
at all times. This means they must learn a tremendous number of
commands, understand how to act in a large variety of situations,
and recognize threats to their human companion, some of which
they might never before have encountered.
Many owners of livestock guardian breeds believe
that breeds like the Great Pyrenees or the Kuvasz are not easily
trained because their stubborn nature prevents them from seeing
the point of such commands as “sit” or “down”.
Hounds may also suffer from this type of ranking. These dogs are
bred to have more of a "pack" mentality with other dogs
and less reliance on a master's direct commands. While they may
not have the same kind of intelligence as a Border Collie, they
were not bred to learn and obey commands quickly, but to think
for themselves while trailing game.
Human relationships
A U.S. Army Staff Sgt. and his military working dog wait at a
safe house before conducting an assault against insurgents in
Buhriz, Iraq on April 10, 2007.Dogs are highly social animals.
This can account for their trainability, playfulness, and ability
to fit into human households and social situations. These attributes
have earned dogs a unique position in the realm of interspecies
relationships despite being one of the most effective, voracious,
and potentially dangerous predators. Dogs and humans at times
co-operate in some of the most effective hunting in the animal
world; in that context, dogs are superpredators.
The loyalty and devotion that dogs demonstrate
as part of their natural instincts as pack animals closely mimics
the human idea of love and friendship, leading many dog owners
to view their pets as full-fledged family members. Conversely,
dogs seem to view their human companions as members of their pack,
and make few, if any, distinctions between their owners and fellow
dogs. Dogs fill a variety of roles in human society and are often
trained as working dogs. For dogs that do not have traditional
jobs, a wide range of dog sports provide the opportunity to exhibit
their natural skills. In many countries, the most common and perhaps
most important role of dogs is as companions.
Dogs have lived and worked with humans in so many
roles that their loyalty has earned them the unique sobriquet
"man's best friend".[33] However, some cultures consider
dogs to be unclean. In some parts of the world, dogs are raised
as livestock to produce dog meat for human consumption. In many
places, consumption of dog meat is discouraged by social convention
or cultural taboo.
Dog communication
Main article: Dog communication
Reproduction
Dogs develop their own societies. Puppies participate with their
littermates in learning to relate to other dogs. Dogs learn to
successfully relate to other dogs by keeping the peace, rather
than by constantly fighting to reestablish this hierarchy.
Differences from other canids
Despite common belief, domestic dogs can be monogamous [34]. Breeding
in feral packs can be, but doesn't have to be restricted to a
dominant alpha pair (despite common belief, such things also occur
in wolf packs[35]). Male dogs are unusual among canids by the
fact that they mostly seem to play no role in raising their puppies,
and do not kill the young of other females to increase their own
reproductive success.[32] Some sources say that dogs differ from
wolves and most other large canid species by the fact that they
do not regurgitate food for their young, nor the young of other
dogs in the same territory.[3] However, this difference was not
observed in all domestic dogs. Regurgitating of food by the females
for the young as well as care for the young by the males has been
observed in domestic dogs, dingos as well as in other feral or
semi-feral dogs. Regurgitating of food by the females and direct
choosing of only one mate has been observed even in those semi-feral
dogs of direct domestic dog ancestry. Also regurgitating of food
by males has been observed in free-ranging doemstic dogs.[36]
So it is sometimes suggested, that the absence of this behavior
was unknowingly caused by artificial selection by humans.[37]
[38]
Life cycle
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Main article: Canine reproduction
In domestic dogs, sexual maturity (puberty) begins to happen around
age 6 to 12 months for both males and females, although this can
be delayed until up to two years old for some large breeds. Adolescence
for most domestic dogs is around 12 to 15 months, beyond which
they are for the most part more adult than puppy. As with other
domesticated species, domestication has selectively bred for higher
libido and earlier and more frequent breeding cycles in dogs,
than in their wild ancestors. Dogs remain reproductively active
until old age.
An Australian Shepherd Puppy Red MerleMost female dogs have their
first estrous cycle between 6 and 12 months, although some larger
breeds delay until as late as 2 years. Females experience estrous
cycles biannually, during which her body prepares for pregnancy,
and at the peak she will come into estrus, during which time she
will be mentally and physically receptive to copulation.
Dogs bear their litters roughly 56 to 72 days after
fertilization, although the length of gestation can vary. An average
litter consists of about six puppies, though this number may vary
widely based on the breed of dog. Toy dogs generally produce from
one to four puppies in each litter, while much larger breeds may
average as many as 12 pups in each litter.
Spaying and neutering
Main article: Spaying and neutering
Neutering (spaying females and castrating males) refers to the
sterilization of animals, usually by removal of the male's testicles
or the female's ovaries and uterus, in order to eliminate the
ability to procreate, and reduce sex drive. Neutering has also
been known to reduce aggression in male dogs, but has been shown
to occasionally increase aggression in female dogs.[39]
A Catahoula Leopard mother nursing her litter of puppies.Animal
control agencies in the United States and the ASPCA advise that
dogs not intended for further breeding should be neutered so that
they do not have undesired puppies.[40]
Because of the overpopulation of dogs in some countries,
puppies born to strays or as the result of accidental breedings
often end up being killed in animal shelters. Neutering can also
decrease or eliminate the risk of hormone-driven diseases such
as mammary cancer, as well as undesired hormone-driven behaviors.
However, certain medical problems are more likely after neutering,
such as urinary incontinence in females[41] and prostate cancer
in males.[42] The hormonal changes involved with sterilization
are likely to somewhat change the animal's personality, however,
and some object to neutering as the sterilization could be carried
out without the excision of organs.
It is not essential for a female dog to either
experience a heat cycle or have puppies before spaying, and likewise,
a male dog does not need the experience of mating before castration.
Female cats and dogs are seven times more likely
to develop mammary tumors if they are not spayed before their
first heat cycle.[43] Dog food containing soybeans or soybean
fractions have been found to contain phytoestrogens in levels
that could have biological effects when ingested longterm.[44]
Gender-preservative surgeries such as vasectomy
and tubal ligation are possible, but do not appear to be popular
due to the continuation of gender-specific behaviors and disease
risks.
Overpopulation
United States
According to the Humane Society of the United States, 3–4
million dogs and cats are put down each year in the United States
and many more are confined to cages in shelters because there
are many more animals than there are homes. Spaying or castrating
dogs helps keep overpopulation down.[45] Local humane societies,
SPCAs and other animal protection organizations urge people to
neuter their pets and to adopt animals from shelters instead of
purchasing them. Several notable public figures have spoken out
against animal over population, including Bob Barker. On his game
show, The Price Is Right, Barker stressed the problem at the end
of every episode, saying: "Help control the pet population.
Have your pets spayed or neutered." The current host, Drew
Carey, makes a similar plea at the conclusion of each episode.
Homeless dog in streets of Bogota Colombia
Working, utility and assistance dogs