The evolution of the dog from wild predator to
domestic companion has been greatly influenced by
human intervention. It has taken just a few hundred
years to produce seemingly endless variations on the
canine theme—but planned breeding has not removed
the basic characteristics of the dog’s ancestor, the wolf.

Evolution of the dog

All dogs share a common ancestor: the gray wolf. While this
relationship is fairly apparent in breeds such as the German
Shepherd or Spitz-type dogs, with their wolflike heads and
pricked ears, it is hard to see the connection between wolves
and toy Poodles or Saint Bernards. Genetically, however,
any dog of any breed is virtually identical to the wolf.
The transition from wolf to the huge diversity of domestic
dogs known today happened relatively quickly. The process
began gradually, with random changes in size and shape,
but accelerated when humans began to selectively breed
those dogs that exhibited characteristics they desired.

In from the wild
Dogs were the first animals to be domesticated, but exactly
when and where wolves came in from the wild to take their
place at human hearths is still under debate. Archaeological
investigations have helped to narrow down the possibilities.
The earliest findings of human skeletons buried with their
dogs are in the Middle East, suggesting that this is the most
likely region for the beginnings of the dog’s development
from wild wolf to domestic animal, which is thought to
have taken place around 15,000 years ago.
It is probable that wolves crept up to tribal camps,
attracted by food and waste scattered around the
perimeters. At first these opportunist wolves may have
been killed for their skins and meat. Over time humans
started to tame and hand-rear orphaned wolf cubs, which as
social animals took readily to adoption by the human “pack.”
Once their potential was recognized—as hunters and natural
guardians that raised the alarm when intruders approached—
the wolves were put to work by the tribe, and the
domestication of the dog was under way. It is surmised that
in an early form of deliberate selection, human-reared

The canid family are shaped to be
efficient hunters. This Weimaraner
remains true to his ancestral body plan
and can move with speed and grace.
Doing things cooperatively is an inbuilt
canine characteristic. Most domestic dogs
look to humans as their pack leaders.
wolves with particular promise—
perhaps being stronger or easier
to tame than others, or possessing
an exceptional nose for game—were
used for breeding. Many hundreds
of years passed before deliberate
breeding became more sophisticated, selecting for
refinements of coat types and colors, temperament, and
specialized skills, and eventually creating hundreds of
different types of dog in a multitude of shapes and sizes.
The selection processes used by breeders to introduce
desirable traits have altered over the years, and while
certain characteristics fall out of favor others become
embedded in the breed standard. Many new breeds
have been introduced in the last 150 years.

In the past the history of a dog breed was pieced together
from written records, pictures, and information handed down
from past breeders and owners. Today the analysis of DNA
(the hereditary template found in body cells) has made it
possible to track the inheritance of features such as size and coat color, and to look at the differences and similarities
between one breed and another. Most importantly, looking at DNA has made it possible to identify which breeds are
at risk of specific genetic diseases and conditions (seepp.338–39). Scientists sequenced the first complete dog
genome (the complete set of genetic information possessed by an organism) in 2005 using the DNA of a Boxer.
Even with the use of genetic analysis, unraveling the history of a particular breed is not easy. Some
breeds are commonly said to be very ancient, but genetic evidence
suggests that the majority are, in fact, modern recreations. With few exceptions, most breeds known
today were developed no earlier than the 19th century.

Dog anatomy
The physical characteristics of a dog are typical of a predator whose survival relies on efficiency in locating and catching prey.Humans have done much to adapt canine design, but the basic anatomy of all breeds of dog is the same.
The skeleton of the dog evolved to provide speed, strength, and maneuverability. A highly flexible spine and
freely moving forelimbs allow a dog to move with a long, swinging stride. The most important characteristics of a
dog’s skeleton are seen in the legs. The two large forearm bones, the radius and the ulna, are locked together in such
a way that a dog can make rapid changes of direction without the bones rotating and breaking. In a further
adaptation, two of the wrist bones are fused together—unlike the separate bones seen in humans—to give a dog strength
and stability when moving in a straight line. Combined with long, powerful toes, with claws like spikes on running shoes,
this limb arrangement gives a dog a high degree of control whether it is running, jumping, or turning.
Classified as carnivores, dogs are anatomically adapted to eat primarily meat, although, given the opportunity,
domestic dogs will eat almost anything. A dog’s teeth are designed to deal with tough foods such as hide, flesh, and bone. Four large canine teeth at the front of a dog’s mouth are used for grabbing and biting prey, while the sides of the
jaw include specially modified teeth, the carnassials, which the dog uses for shearing off meat. Dogs have a capacious
stomach for the storage of large quantities of food and, since meat can be digested rapidly, a short intestinal tract.
Dogs have a wide-angled field of vision that functions best at long distance and they are extremely sensitive to
movement. Out of the corner of an eye, a dog can pick up the flicker of a rabbit a hundred feet away, but at close
range, canine vision is less efficient, which is why a dog may fail to spot a toy on the ground in front of his nose. Dogs
have little use for sophisticated color vision and their eyes have far fewer color-receptive cells than those of humans.
Sharp hearing and the ability to pinpoint the direction of sounds is essential to wild hunting dogs. Breeds with erect
ears shaped like those of the wolf are likely to have more acute hearing than breeds with drop ears, which rely more
on sight or scent when hunting. A dog’s highly sensitive ears allow it to pick up sounds at a far higher frequency
than can be heard by humans. Smell is the most important of all canine senses. Sniffing is the way a dog reads its surroundings and the area of the brain that interprets smells is around 40 times larger than the corresponding area in a human brain. Dogs’ noses are packed with far more scent receptive cells than humans: while a
person has an estimated 5 million scent receptors, a small dog may have closer to 130 million.
In breeds renowned for their scenting ability, such as hounds, the number of scent receptors may be as many as 200–300 million.
Unlike humans, dogs do not have sweat glands in their skin, except on the bottoms of their paws. To cool down dogs must pant, tongue hanging out. The tongue produces copious saliva, some of which evaporates and so helps to reduce body temperature.

Head shapes
Canine heads are all variations on three basic shapes. The majority of dogs have a mesaticephalic head, in which length and width are of medium proportions. A dolichocephalic head is
long and narrow, with a barely noticeable stop. Brachycephalic heads are broad based and short in length.

Ear types
Pricked, sensitive wolflike ears—the original canine shape occur in many breeds of dog, but centuries of planned selection have created a large variety of other ear shapes. There are three main types: erect, semierect, and drop. Within these categories are many variations, such as the type of erect ear known as candle flame. Ear types are often the defining characteristic of
a dog group; for example, scent hounds usually have long, pendant ears. Ears strongly influence a dog’s overall appearance. The correct set, shape, and carriage of the ears are considered very important in recognized breeds,
and are described precisely in official breed standards.

Coat varieties
The majority of dog breeds have a double coat like their wolf ancestor.
This usually consists of an insulating layer of soft, dense hair covered by a harsher outer coat of varying length and texture. A few thinner-coated breeds, such as greyhounds, have just
a single layer of hair (no undercoat). In some breeds, chance genetic mutation has produced dogs that are either completely hairless or have just a few strands of hair on the head and legs.

Breeds and breed groups
Although many distinct varieties of dog were recognized
earlier, until the early 20th century their breeding was not
necessarily strictly controlled. When dog breeders started
to cooperate with one another and form clubs they were
able to produce dogs of consistent type. This led to the
writing of breed standards that describe the ideal
appearance (with permissible variations) and temperament
of a breed, and its suitability for function. Dogs were also
registered in stud books to enable their pedigrees to be
reviewed for future breeding.
Despite the detailed dog breed standards that exist, there
are as yet no universally recognized criteria for classifying
dog breeds in groups. The main regulatory bodies are the
Kennel Club (KC) in the UK; the Fédération Cynologique
Internationale (FCI)—the World Canine Organization, which
includes 86 member countries; and the American Kennel
Club (AKC). These all group breeds together based loosely
on function, but no two systems are exactly the same. Both
the UK and American Kennel Clubs recognize seven groups,
while the FCI has ten. The number of individual breeds
recognized by these organizations also varies.
This book places breeds together in eight major groups:
primitive dogs; working dogs; spitz-type dogs; sight hounds;
scent hounds; terriers; gundogs; and companion dogs; plus
a section on crossbreeds and random bred dogs. The
groupings of the so-called primitive dogs, sight hounds, and
the spitz-type dogs have been made on the basis
of well-established genetic relationships. In some cases, this
results in a breed appearing in a different group from the
one that might be expected. The Basenji, for example, is
often grouped functionally with hounds but genetic evidence
places it among the primitive breeds. For the remainder of the groups, more traditional, functional groupings are used.