By John von Radowitz, Science Correspondent.
IT'S A DOG'S LIFE SCIENCE
Man and his best friend have been close companions for a long time.
Recent studies suggest that dogs trotted alongside the first people to cross the Bering Strait and bring humanity to the New World.
Domestic dogs emerged at least 14,000 years ago - possibly a lot further back, according to some scientists.
As millennia past, dogs and humans evolved together. Dogs were used as sentinels, hunting companions, weapons of war and gods to be worshipped.
Their close association with people has also turned them into keen readers of human behaviour. In some ways, dogs understand humans better than our closest relative, the chimpanzee.
Genetic research indicates that all dogs, from dobermans to dachsunds, are descended from wolves.
One study comparing DNA taken from blood, tissue or hair samples from 140 domestic dogs and 162 wolves from three continents found that they differed by only 1%.
Robert Wayne, of the University of California at Los Angeles, who led the investigation, concluded that the genetic split between wolves and dogs occurred 135,000 years ago.
There's no archaeological or fossil evidence to support this date. But what is known is that the earliest dog remains, a short jawbone with crowded teeth found in the Middle East, date to about 14,000 years ago.
An Asian origin for dogs is supported by the fact that there are more genetic types of dog in countries such as China, Thailand, Tibet, Korea and Japan than in Europe, Africa and Arctic America.
No-one knows quite how the domestic dog, Canis familiaris, emerged from the wolf, Canis lupus.
One theory is that during the Stone Age men adopted wolves to guard their homes and serve as hunting companions.
Another is that women developed a soft spot for wolf puppies. The most likely scenario is that some wolves started hanging around early villages and became scavengers, feeding off human scraps.
Fossils found in China and England suggest that wolves and neanderthals shared close quarters as far back as 400,000 to 500,000 years.
Eventually, these wolves may have formed a symbiotic relationship with humans and evolved - partly through deliberate breeding - into domestic dogs.
A genetic study by Jennifer Leonard, from the Museum of Natural History in Washington DC, showed that dogs from at least five domestic lineages probably accompanied humans across the land bridge from Siberia to Alaska between 14,000 and 12,000 years ago.
Her team looked at mitochondrial DNA, which is situated outside the cell nucleus and only passed on down the female line. Without the shuffling of genes that occurs in nuclear DNA, it can be used to trace lineages back to remote ancestors.
These early dogs would not have been mere pets. Scientists think they must have provided a useful function - possibly to guard encampments, for transport, and for herding buffaloes or mastodons in hunts.
Native Americans revered dogs. In the Cherokee culture they were used to guard camps and fields, and given a special place in ritual and legend. The Sioux used dogs to move camp, each family using between six and 12 dogs to help carry their belongings.
Dog tradition is rich and varied in the Old World. The ancient Egyptians held dogs in such esteem that harming one was a punishable offence.
Early Egyptian culture is full of wall paintings and sculptures depicting lean hounds in hunting stance or seated with their masters. The Egyptian nobility favoured dogs that looked similar to present day pharaoh and Ibizan hounds. Dogs played a big part in the spiritual life of the ancient Egyptians, too. The dog god Anubis was worshipped as the judge and lord of the Afterlife.
According to legend, the builders of Rome, Romulus and Remus, were orphans taken in and suckled by a she-wolf. Historians have since speculated that the animal could have been a wolf-dog hybrid.
The Roman empire became a melting pot of dogs from all its conquests. As in ancient Egypt, Roman dogs served in a variety of roles, from companions and guard dogs to vicious fighting dogs pitted against slaves and wild animals.
The proverbial "dogs of war" were also Roman. Huge and fearsome Molossians, which resembled giant Rottweilers, were sent into battle to kill and dismember the enemy.
Mollosian, now extinct, originally came from Greece, where they were also used for fighting. Alexander the Great owned a Mollosian named Peritas who, legend has it, killed a lion and an elephant in fighting matches.
Roman citizens sometimes had Mollosian guard dogs. In Pompeii, archaeologists have found mosaics depicting Mollosians outside people's homes with the message cave canem - "beware of the dog".
Large dogs, similar to mastiffs, were also used in ancient China to guard sheep. The Venetian explorer Marco Polo reported that the Mongol ruler Kublai Khan had 10,000 hunting hounds which were attended by the same number of men.
Several hundred years before Kublai Khan, Emperor Ling gave his dogs royal status. Little pug-faced dogs were suckled by wet nurses, given an allowance and guarded by eunuchs.
As in Egypt, dogs played an important part in Chinese spiritual life. Early chow chows, for instance, served as temple guards.
During the middle ages, hunting became a major status sport, creating a large dog industry.
Monasteries became centres of dog breeding. The Belgian Benedictine monastery of Saint Hubert became known for breeding early bloodhounds, possibly by crossing Roman Mollasians with mastiffs. William the Conqueror is said to have used the dogs to track down his enemies and guard his camps.
Renaissance noblemen competed for the best hunting dogs, and tried to create their own exclusive breeds. Many of these gave rise to breeds we recognise today.
Companion breeds such as spaniels and terriers also started to proliferate at this time. Often, these "lap dogs" were dressed in ribbons, jewels and doll's clothes.
Such a long and close history has led to a deep understanding between us and our four-legged friends. Scientists have found that dogs pick up human hints about hidden food better than chimpanzees. Puppies of all ages excel at following a human's gaze or pointing finger, even if the animals have had little experience of people.
Chimps, on the other hand, co-operate and communicate with humans very poorly.
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