A recent study gave results that humans have systematically altered the brains of dogs through selective breeding for favored behavioral traits over hundreds of years. The researchers investigated the effects of this kind of selective breeding on the brain structure of canines by analyzing MRI scans of 33 dogs.

The team observed vast differences in the brain structure, not only related to the body size or head shape of dogs, but to the patterns in neural networks associated with different brain functions.

The researchers noticed that there is a hundred-fold difference between the body mass of a Chihuahua and the body mass of a great dane. By comparing dachshund’s brain and golden retriever brain scan images, the researchers found that the dachshund’s brain takes up most of the available endonasal space, while the golden retriever showed noticeably larger sinuses.

While comparing the evolutionary lineages of the dog breeds, the team revealed that change in relative brain size is not predicated by relatedness.

The study showed that this is caused by the human selection for specific traits of dogs occurring more recently across the tree of dog evolution.

When the researchers examined the areas of the brains with the most variations across breeds, they made the map of 6 brain networks, with the proposed functions varying from social bonding to movement. Each of these were associated with at least one behavioral characteristics. The difference in behaviors across breeds was linked to the anatomical difference in the six brain networks.