Researchers have found that dogs are capable of understanding up to 250 words and gestures, can count up to five and can perform simple mathematical calculations.
Using tests originally designed to demonstrate the development of language, pre-language and basic arithmetic in human children, the researchers were able to show that the average dog is far more intelligent than they are given credit for.
They have also compiled a list of the most intelligent and least intelligent breeds using information from obedience classes. Border collies and retrievers were rated among the most intelligent while hounds and terriers were the least bright.
"The average dog is about as bright linguistically as a human two-year-old," said Professor Stanley Coren, a leading expert on canine intelligence at the University of British Columbia in Vancouver who has carried out the work.
"This means they can understand about 165 words, signs and signals. Those in the top 20 per cent were able to understand as many as 250 words and signals, which is about the same as a two and a half year old.
"Obviously we are not going to be able to sit down and have a conversation with a dog, but like a two-year-old, they show that they can understand words and gestures."
Professor Coren, who presented his work on Saturday at the Annual Convention of the American Psychological Association, believes dogs are among the most intelligent animals and can rival apes and parrots for their ability to understand language.
While most dogs understand simple commands such as sit, fetch and stay, a border collie tested by Professor Coren showed a knowledge of 200 spoken words. The collie was able to recognise the names of items it was asked to fetch and correctly retrieve them.
The dog was also quick to learn the names for new items and after being taught a new word, brought back the correct item 70 per cent of the time. Other dogs have shown similar abilities, although often with fewer words but with gestures instead.
Professor Coren has also found that dogs can count using established tests developed for young children. When something unexpected happens with an object, children and dogs will stare at it for a longer period of time.
By lowering a dog treat behind a screen and then another, the dog would expect to see two dog treats, but if a treat is secretly removed or another one added, the researchers found dogs would stare for longer at the treats when the screen was removed.
Professor Coren said: "Dogs can tell that one plus one should equal two and not one or three.
"They can also deliberately deceive, which is something that young children only start developing later in their life."
A survey of more than 200 dog obedience judges in the US and Canada has also helped to reveal the most intelligent breeds. Border collies were rated as the most intelligent while Afghan hounds were the least intelligent.
Professor Coren believes centuries of selective breeding and living alongside humans has helped to hone the intelligence of dogs.
He said: "If you look at wild wolves, they do not perform as well as domestic dogs. When a human points, the wolf will look at the finger, while the domestic dog will look where the finger is pointing.
"For some of the older breeds like hounds and terriers, they were bred to hunt and run prey down for humans while other breeds such as collies and retrievers were bred to follow commands."
There is now a growing body of research that is showing other domesticated animals are in fact more intelligent than was previously thought. Recent research at Essex University showed that horses are capable of counting.
Professor Marc Bekoff, an ecologist at University of Colorado, Boulder, said: "Domestic animals are incredibly smart and emotional.
"They do many things that their wild relatives cannot do because of their close association with humans over long periods of domestication and we can learn a lot about their wild relatives by studying dogs as I have done with social play."
Allan Brooks, an Afghan Hound breeder from Co Durham and international show judge, said: “Afghan hounds are not at all stupid. They have got one hell of a long memory.
“They can act like a bit of clown and like to cause a riot, but they have got far more brains than a lot of breeds.”
Ten most intelligent breedsBorder Collie
Poodle
German Shepherd
Golden Retriever
Doberman Pinscher
Shetland Sheepdog
Labrador Retriever
Papillon
Rottweiler
Australian Cattle Dog
Least intelligent breedsAfghan Hound
Basenji
Bulldog
Chow Chow
Borzoi
Bloodhound
Pekinese
Beagle
Mastiff
Basset Hound
http://www.telegraph.co.uk/science/science-news/5994583/Dogs-as-intelligent-as-two-year-old-children.html
