A new study has found that certain modern dog breeds have larger brains compared to ancient dog breeds thousands of years old. This is true for the modern dog breeds that are genetically more distant from wolves. The study, led by Hungarian and Swedish researchers, was recently published in the journal Evolution.
Preparation for the study took several decades.
Role of urbanisation and complex social environments in brain size evolution
The roles or life history characteristics of these dog breeds are not responsible for their increase in brain size. Rather, their brain sizes are likely to have been influenced by urbanisation and a more complex social environment, a statement released by the Elte Institute of Biology said.
According to the institute, this is the first comprehensive study regarding the brain size of different dog breeds.
Domestication leads to reductions in brain size, but not much is known about how brain size evolved after domestication, and whether artificial selection, which is the identification of desirable traits in plants and animals by humans, can compensate for domestication efforts, the authors noted in the study.
Dogs were the first animal to be domesticated. There are more than 400 dog breeds on Earth, and these have developed relatively quickly and exhibit great diversity.
The study found that wolves with an average body weight of 31 kilograms have an average brain volume of 131 cubic centimetres, while dogs with a similar weight have a brain volume of about 100 cubic centimetres, which is about three-quarters of the brain volume of wolves of this weight. The authors noted that this confirms the fact that domestication has led to a decrease in brain size in dogs.
However, they also found that the more genetically distant a dog breed is from wolves, the larger its brain size is.
In the statement, László Zsolt Garamszegi, the lead author on the paper, said the brains of domesticated animals can be up to 20 per cent smaller than those of their wild ancestors probably because the lives of domesticated species are simpler compared to those of their wild counterparts.
He also explained that domesticated animals do not need to fear predator attacks or hunt for food in the safe environment provided by humans, and therefore, there is no need to sustain the energetically costly large brain, and the freed-up energy can be directed towards other purposes such as producing more offspring.
Quoting Niclas Kolm, one of the authors on the paper, the statement said different dog breeds live in varying levels of social complexity and perform complex tasks, which likely require a larger brain capacity. Therefore, he said, the researchers hypothesise that the selective pressures on the brain can vary within the dog species, and one may find differences in brain size among breeds based on the tasks they perform or their genetic distance from wolves.
The researchers performed computer tomography scans of dog skulls. Kálmán Czeibert, another author on the paper, reconstructed the brains of dog breeds and determined their exact volume, based on the computed tomography images. They gathered data from 865 individuals, which represent 159 dog breeds. As many as 48 specimens represented wolves.
In the statement, Enikő Kubiyini, one of the authors on the paper, said the domestication of dogs began approximately 25,000 years ago, but for 10,000 years, dogs and wolves did not differ in appearance.
She explained that many ancient breeds, such as sled dogs, still resemble wolves today.
Kubiyini said that a significant portion of the distinct-looking breeds known today has only emerged since the industrial revolution, primarily in the last two centuries, as dog breeding has become a hobby.
The authors concluded that skull shape, original role of the breeds, longevity and litter size were not associated with brain size. This implies that brain size evolution in domesticated species is not influenced by selection for performing specific tasks, morphology and life history.