London: Domestication by humans helped dogs evolve bigger brains making them more friendly than their feline counterparts and other solitary species, say scientists.
The reason, they suggest, is that dogs evolved bigger brains because friendly, social mammals need more grey matter than solitary, aloof ones.
The findings come from a study into the brain size of more than 500 species of living and fossilised mammals, reports the journal Proceedings of the National Academy of Sciences.
The Oxford University researchers charted the evolution of mammal brains over the last 60 million years, from a few million years after the dinosaurs became extinct to the modern day, according to the Daily Mail.
They discovered that there is a strong link between the size of a brain relative to an animal`s body and how sociable that creature is.
Sociable mammals such as whales, dogs, dolphins and humans tend to have much larger brains compared to their bodies.
Solitary species, such as tigers, domestic cats and rhinos, have less grey matter, the scientists found.
Professor Robin Dunbar, study co-author at Oxford, said: "For the first time, it has been possible to provide a genuine evolutionary time depth to the study of brain evolution."
"It is interesting to see that even animals that have contact with humans, like cats, have much smaller brains than dogs and horses because of their lack of sociability."
The study found that the brains of monkeys expanded the most over evolutionary history, followed by horses, dolphins, camels and dogs.
Researchers believe that living in a group is more demanding mentally than having a lonely existence.