Pet owners' desire for attractive-looking dogs has led to a decline in intelligence of the pooches, according to Swedish scientists.
Researchers have suggested that breeding modern dogs for their appearance has eroded the mental agility and alertness of the working breeds from which they are descended.
The behavior expected of them is to be friendly and docile at home, rather than alert and aggressive outside, reports Times Online.
Kenth Svartberg, author of the Swedish research, said the changes in intelligence had happened over just a few generations.
"Modern breeding practices are affecting the behavior and mental abilities of pedigree breeds as well as their physical features," he said.
Researchers believe that many breeders concentrate on outward aspects and ignoring the mental qualities of dogs to appeal to modern pet owners and the dog shows that dictate the characteristics of pure breeds.
To reach the conclusion, Svartberg, who carried out his research at Stockholm University, gave 10 tests to 13,000 dogs to rate 31 breeds on characteristics such as sociability and curiosity.
He found that, in general, animals that were bred for appearance, and especially for shows, displayed reduced levels of all these qualities.