There are several ways in which the evolution of a species can be traced - but none of the existing records are complete, even for humans. As a result, we have to speculate about the missing "links" in the evidence.
In zoological classification dogs belong to the Class Mammalia (mammals - they are hair covered animals that feed their young with breast milk ), the Order Carnivora (they are carnivores - they eat meat) and the Family - Canidae. Within this family there are further subdivisions called genera, and each genus contains individual species. A species of dog is a group that normally breed and produce fertile offspring.
Members of the family Canidae (domestic dogs, gray wolves, dingos, coyotes and jackal) now inhabit all parts of the world. Except for domesticated dogs the others in the family are restricted in distribution to areas inhabited by their prey. Before modern times, dogs were found on all continents except for Antarctica.
General characteristics of
In the wild dogs have evolved as predatory hunting animals with speed, power and keen senses - particularly hearing, sight and smell. From only a few weeks of age puppies show instinctive behaviour typical of hunter-killers. They are extremely alert to sounds and movements, stalk, ambush, and they demonstrate in play-fighting the biting actions around the neck needed to bring down and kill prey quickly. Gun dog puppies (and other breeds) instinctively know from an early age how to chase and retrieve balls and other toys.
Dogs are social animals, and in the wild tend to live in packs. They are also good at working together in teams but this requires a hierarchy or pecking-order within the pack - and dogs are good at learning their place in a "family". This makes them ideal companions for humans who can assume the role of "pack-leader" within their social group - the household.
The earliest ancestors of dogs originally evolved about 200 million years ago from reptiles. Prehistoric remains of dogs are few and far between but the dental pattern of modern day dogs is similar to that found in fossilised creodonts - primitive fish-eating mammals which lived about 50 million years ago, but this genetic line failed to survive and there are no direct descendants today. At the same time another group of animals the miacids also had dog-like cutting teeth - they were small forest-dwelling creatures (not unlike polecats) and these evolved into the carnivores of today - including some dogs.
By about 1 million years ago (the Pleistocene period - half a million years ago) there were a variety of larger dogs and the family Canidae (wolves, coyotes, jackals and foxes) was formed. It is generally agreed that the common ancestor to domesticated dogs was a form of wolf found on the plains of India.
The oldest authenticated skeletons (note these are true skeletons - not fossils) of dogs have been found in Denmark and are estimated to be 8000 BC. Skeletons of dogs have been found in Jarmo (Iraq) dating from 6750 BC, and in the ruins of Jericho from 6500 BC. The first evidence of dogs in Egypt date from 3500 BC.
Existing "Wild dogs" - the African hunting dog, South American bush dog and Indian dhole are not close relatives of the domesticated dog - only sharing a common ancestry some 20 million years ago in the Oligocene period. Foxes and wolves on the other hand have a common ancestor 7.5 million years ago in the Miocene period.
Based upon archaeological evidence domestication of dogs is thought to have started about 10,000 years ago - a lot earlier than the domestication of cats. Indeed, by the time man reached Denmark in Europe in neolithic times he had a domesticated dog with him. Some of the earliest references to dogs living with humans can be found in Sumarian writings from 5000 years ago. Dogs found in Stone Age human settlements were very similar to todays Eskimo dogs.This means that dogs have had thousands of generations in which to undergo the genetic changes that have lead to such a wide variety of different forms. The earliest dogs to be found in North America date from 1500 BC… suggesting that they were introduced from Europe.
The reason why domestication initially occurred is a matter of speculation. However, some of the reasons may still be evident today. If one looks at the modern world wild dogs (and other wild animals) will visit human settlements to scavenge for food and, over a period of time a trust can build up which will allow humans to handle these animals. It is likely that early domesticated dogs gained the benefit of food leftovers and scraps. Meanwhile humans benefited from the security of having dogs around their encampment which would detect the approach of unwelcome visitors (wild animals or other humans) and act as a warning system by barking.
It is not surprising that dogs were trained to work alongside men, because they are social animals that respond to positive and negative stimuli and respect a hierarchical structure, which humans can easily dominate. In addition, many of the natural hunting traits that dogs instinctively possess - the use of smell to detect and track prey, and the chase of food quarry are typical of the working uses made of dogs throughout history.
The emotional bond that exists between many humans and pet dogs is more complex to explain, but it is clear that both parties get fulfilment and share enjoyment out of the dog's role as a member of a human household. Toy breed lap dogs have been as popular as pets for as long as the working breeds. A small white, long-coated Maltese dog - not unlike to current Maltese Terrier, is depicted on a vase dating from 500BC, and similar dogs were kept by the Ancient Greeks.
Throughout recorded history dogs have accompanied man, and they have been given religious significance in several countries. In China and amongst the North American Indians it was believed that dogs would escort the dead safely to the underworld. Valuable breeds (such as Salukis) were given as gifts to important dignitaries, and dogs with special skills or possessing unusual characteristics have always been of interest and treated and traded like commodities. Unfortunately, as with all "commodities", fashions change and breeds fall in and out of popularity.
The greyhound (or gazehounds or gase hounds, as they were known because they hunted by sight and relied on speed to catch their quarry) is generally regarded as being the earliest pure-bred type of dog. This is based on records from Ancient Egypt. The word greyhound is believed to be a corruption of "Greek hound" because the Ancient Greeks used to hunt hare with these dogs and also had other hounds for boar and deer hunting. The early greyhounds were large with upright ears like Pharoah Hounds and Ibezan Hounds and they were transported with Phoenician traders. It is known that the Phoenecians traded for tin in Cornwall as early as the 4th Century and it is likely that they brought dogs with them. Greyhounds have always been used for coursing and in 1776 a code was written for the sport. Whippets are relatively recent variety.
Other breeds depicted in early Egyptian images are Saluki -type hounds on the walls of the tomb of Rekhma Ra (1400BC), the Afghan and the Basenji. These recordings suggest that dog breeding was probably occurring nearly 4000 years ago in 2000 BC. By the time of Christ, 2000 years ago, Gratius Faliscus, a Roman poet, listed 22 breeds of hunting dog of which only one originated in Italy - the rest were imported from other countries. Unfortunately, no images survive to illustrate these different breeds. Toy lap-dogs were also popular as companions in Pre-Christian times, and dwarf legged dogs (not dissimilar to the Basset Hound) were recorded in Ancient Egypt and China where they were used for falconry.
Pre-600 BC the Ancient Greeks and Romans hunted boar with a larger, heavier dog called a Molossus, and this dog was very similar in stature to a Mastiff. Assyrian Mastiffs were used to hunt lion and for use in war by Assur-banipal in 625 BC. Two types of Molossus were evident by the time of Aristotle - one used for hunting, the other for herding and guarding livestock. In Rome Mastiff-type dogs were used in gladiatorial fights with wild animals and in Britain and other countries descendants of these types of dogs were later used for Bull, Bear, Lion and even Horse baiting as well as dog fights- e.g. bulldogs, bull terriers. The Alpine Mastiff ( a long-haired variety) was the predecessor to the St Bernard.
In Russia the Borzoi and Russian Wolfhound were used for hunting and coursing which is well documented in texts dating from the mid-17th Century. The early ancestors of these breeds were from the Mediterranean regions
In Britain greyhound-like dogs such as the Wolfhound and Deerhound were certainly some of the earliest breeds. A gift of Wolfhounds was sent to Rome for Consul Quintus Aurelius Symacchus in 391 BC for a circus.
Arab nomads (the Bedouins) are known to have bred Salukis and allowed this breed to share their tents. This was unusual because dogs generally were regarded as being "unclean" animals.
Until medieval times the most common method of hunting was to use a single dog (hound) to track game by scent, and then the pack was let go. The leashed dogs were called a lyam. Scent hounds are not particularly fast, and rely on endurance to wear out their quarry.
In Europe one of the earliest types of dog has been recorded in Mesolithic human settlements in Denmark. This was a medium-sized Spitz-like dog. These types of dogs are compact, have pointed, prick ears and a bushy tail that is carried curled over the back. Indigenous species occur all over the world indicating that it is indeed and early form of dog. Click here for more information
In Germany the Great Dane used to be called the Great Boarhound reflecting it's origins from the Molossus. The monks of the Hospice of St Bernard first bred the St Bernard in the mid-17th Century as working dogs to help carry loads, as a guide, and for finding paths in the snow.
Larger dogs such as Newfoundlands were used to pull carts and were called draught dogs. Newfoundlands were also used to carry lines from shore to ship, and today swimming is still part of the working test for the breed.
In France hunting dogs were predominantly scent hounds such as St Hubert hounds created by St Hubert - the patron saint of hunting. The black variety of this breed was the predecessor to the modern day Blood Hound, and the white variety was very popular in the Middle Ages and called a Talbot hound - and this was a predecessor to Southern Hound and, later, to the modern day Foxhound. France was also the home of dwarf short-legged dogs - Basset Hounds
In Spain the Spanish Pointer was the main hunting dog, and this was probably the predecessor for other Pointers.
Dingos were companions of the Aborigines who introduced them into Australia in the late Palaeolithic times, and they subsequently became a feral animal, also the Maori's introduced domesticated dogs to New Zealand.
Spaniels are mentioned in Ireland in Laws written in 17 AD and they were used throughout the Middle Ages for falconry. Spaniels were divided into land spaniels (later Springer and Cocker Spaniels) and water Spaniels (including the Irish Water Spaniel but also others - including Poodles). In the mid-17th Century water spaniels were clipped like modern day Poodles - to facilitate swimming.
Cats have specific anatomical features which are common to all species but the same is not true for dogs. Thanks to thousands of years of selective breeding and spontaneous genetic variants dogs now come in such a wide variety of physical forms -different sizes - from Chihuahuas to Great Danes, and different shapes - from Greyhounds to English Bulldogs - that generalisations are not always possible.
Male and female dogs are very similar in appearance though males are usually slightly bigger than females of the same breed.
Dogs run on their toes , and have four functional toes on both the front feet and the hind feet, and sometimes a fifth "dew claw" which serves no useful purpose, is not in contact with the ground, and is located higher on the inside of the leg. Dogs have soft pads on the toes and feet which help to reduce sound when stalking, as well as protecting the underlying bones and joints from concussion during running and jumping.
Dogs have evolved in a variety of ways - for hunting some rely on eyes that are placed forwards on the head giving them good forward and sideways vision (so-called sight hounds). Other breeds rely much more on their sense of smell and have extremely well developed nasal structures. The hounds and spaniels are good examples of "scent" dogs and these have the most sensitive chemical detecting device known to man - a nose that can detect only a few molecules of substance. They are far superior to any artificial detecting devices so far developed - which is why these breeds are so useful in detecting drugs, explosives, fruit and, of course, people.
Dogs have a dental profile typical of the carnivores and there is remarkable similarity between wolves, coyotes, jackals and dogs when their skull dimensions are compared. Dogs have four large canine teeth at the front of the mouth which are used to grasp their prey, and large molars including two carnassial teeth (one on the upper arcade of both sides of the mouth). These are used to gnaw and slice the meat into small pieces so that it can be swallowed.
However, although classified as Carnivores dogs have actually evolved as omnivores and they can be fed an exclusively vegetarian ration - unlike cats which are obligatory carnivores. Interestingly, the Chow Chow in China was fed exclusively rice and other cereals - and as a result they were unable to adapt to being fed meat when they were first introduced into Britain. As a result they developed various problems including a poor skin and coat condition.
All dogs have non-retractable claws which sets them apart from all cats except for the Cheetah which also has non-retractable claws.
Dogs have a wide variety of coat types and coat colours - all of which have been selectively bred for by humans. Wild dogs tend to have mixtures of yellow, brown or black hair colouration often in a brindle pattern which provides camouflage.
DNA - Inheritance and gene
Dogs have large number of 78 chromosomes in each cell . The yellow Jackal has 74 chromosomes. Other species of Canidae are different - the red fox has 38 chromosomes, the raccoon dog has 42 chromosomes, and the Fennec fox has 64 chromosomes.
A species of an animal is a group that normally breeds and produces fertile offspring. However, under artificial conditions - such as captivity - it is possible to cross-breed different species and indeed the domesticated dog is reported to have been bred successfully with all other members of the family Canidae. Theoretically the offspring should be sterile but this was not the case when dogs were crossed with wolves.
The anatomical, behavioural and other characteristics of modern-day dogs can be explained by the genetic transfer of material from one generation to another, the principle of "survival of the fittest" and by adaptation to the surrounding environment. Sometimes a desirable trait transmitted by a genetic sequence can be linked to an undesirable trait. The most notable example of this is white hair coat. White dogs are often born deaf, and they are also predisposed to develop hypersensitivity and in some cases cancer - particularly on the bridge of the nose, when exposed to sunlight.
Laboratory sequencing of canine DNA (the canine genome) is currently being undertaken, and as a result we shall discover more and more about the genetic component of inheritance in the different breeds of this species. This will not only help us to prevent and treat common diseases, but it will help us to piece together the evolutionary trail leading to modern day dogs.
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