If humans had never domesticated dogs, they would still be wolves. But around 14,000 years ago, we did, and today we’re left with lovely companions who are forever changed by our interference. A study released Monday in the Journal of Neuroscience shows that the process of domestication not only turned the bodies of wild canines into Pomeranians but also changed the way their brains operate in the process.
To learn this, a team led by Erin Hecht, Ph.D., an assistant professor of evolutionary neuroscience at Harvard University, analyzed the brain structure of 62 dogs representing 33 breeds, including Golden Retrievers, Jack Russell terriers, and Greyhounds. In turn, the magnetic resonance imaging scans revealed that there’s a wide variation in brain structure across dog breeds, and this variation is determined by multiple, interacting factors.
Hecht explains to Inverse that while body size and head shape do play a role in a dog’s brain structure, “over and above those factors, we are also seeing relationships with behavior.” These findings suggest that selective breeding for specific behavioral traits, like hunting and herding shaped different breeds’ brains in unique ways.
In other words, Golden Retrievers and Jack Russell terriers have brains with differing variations not because one is big and the other is small, but because they were bred to do different jobs. This breeding changed their behavior, and that change is physicalized in the brain.
When you average out the intelligence of all dogs, scientists believe they have the same cognitive capabilities as a human toddler. The type of intelligence dogs demonstrate varies across breeds as well, and dog intelligence is broken up into three categories: instinctive, adaptive, and a combined category known as “working and obedience.”
In the book Intelligence of Dogs, canine psychologist Stanley Coren, Ph.D., claimed that the brightest dogs are working dogs who are capable of learning commands after fewer than five exposures and obey at least 95 percent of the time. This group includes Border Collies, Poodles, and German Shepherds. In turn, the alleged “smartest” dog is Rico, a Border Collie who responds to over 200 words. The average dog can respond to 165.
But perhaps Rico has a leg up. He was bred to work, and his brain adapted in turn. Meanwhile, Bassett Hounds were bred to chill out.
Humans have bred different lineages of domestic dogs for different tasks, like hunting, herding, guarding, or companionship. These behavioral differences must be the result of underlying neural differences, but surprisingly, this topic has gone largely unexplored. The current study examined whether and how selective breeding by humans has altered the gross organization of the brain in dogs. We assessed regional volumetric variation in MRI studies in 62 male and female dogs of 33 breeds. Notably, neuroanatomical variation is plainly visible across breeds. This variation is distributed non-randomly across the brain. A whole-brain, data-driven independent components analysis established that specific regional sub-networks covary significantly with each other. Variation in these networks is not simply the result of variation in total brain size, total body size, or skull shape. Furthermore, the anatomy of these networks correlates significantly with different behavioral specialization(s) such as sight hunting, scent hunting, guarding, and companionship. Importantly, a phylogenetic analysis revealed that most change has occurred in the terminal branches of the dog phylogenetic tree, indicating strong, recent selection in individual breeds. Together, these results establish that brain anatomy varies significantly in dogs, likely due to human-applied selection for behavior.