The brains of some dogs are becoming bigger due to the demands of modern life, a study found.
Breeds which are more genetically distant from wolves – such as boxers – have larger brains than those more directly descended from them.
The increase is thought to be due to urbanisation and a complex social environment.
Wolf brains are still larger but the gap is shrinking.
Researchers hope to use the findings to help them understand why human brains are so large compared to body size.
The study was carried out by scientists from Hungary and Sweden. They used CT images of over 850 dogs representing 159 breeds to reconstruct different brains and determine volumes.
They compared findings to 48 wolf specimens.
They said they were surprised that the further a dog breed is genetically distant from wolves, the larger its relative brain size.
Furthest away from wolves are breeds such as boxers, bulldogs, Hungarian Vizslas and Great Danes. Those most similar to wolves include huskies.
Dr Laszlo Zsolt Garamszegi, an evolutionary biologist at the Ecological Research Centre in Hungary, said the findings went against the trend of domestic animals’ brains being smaller than their ancestors.
He said: “In the safe environment provided by humans, there is no need to fear predator attacks or hunt for food. Therefore, there is no need to sustain the energetically costly large brain.”