Humans and dogs share a long, intertwined history; we have been breeding our floofy best buds for thousands of years. All this tinkering with dog DNA has led to a plethora of diverse pooches, from the hulking Great Dane to the tiny chihuahua. And according to a new study published in JNeurosci, by selectively breeding for certain traits, humans have also played a role in shaping dogs’ brains.
Different breeds are well known to boast varying behavioral characteristics. Border collies are keen herders, for instance, while dachshunds will dig up just about anything they can get their paws into; they were, after all, bred to hunt tunneling animals. “These behavioral differences must be the result of underlying neural differences,” the study authors write, “but surprisingly, this topic has gone largely unexplored.”
Hoping to shed new light into dogs’ neural functions, the research team looked at MRIs from 62 dogs belonging to 33 different breeds. The pups had been scanned at the University of Georgia Veterinary Teaching Hospital, and found to be free of any neurological abnormalities. Researchers used American Kennel Club data to group the dogs into different categories based on their “behavioral specialization,” or what appears to have been the original intention for their breed—for instance, scent hunting (basset hounds and beagles), herding (Welsh corgis and old English sheepdogs) and “explicit companionship” (the Maltese and Yorkshire terriers).
The first order of business was determining whether brains varied in form and size from breed to breed—which, perhaps unsurprisingly, they did. As Liz Langley points out in National Geographic, “[D]ogs bred to be small—say the lhasa apso—have round heads with similarly round brains that take up most of their skull. A larger breed like a golden retriever has a long, narrow head, and thus a more elongated brain that doesn't fill all of the skull space.”
But such differences in brain anatomy “go over and above differences in body size, brain size, and just general head shape,” Erin Hecht, an assistant professor of evolutionary biology at Harvard and lead author of the new study, tells Ed Cara of Gizmodo. The researchers examined areas of the brain with the most anatomical variation across different breeds, and used that information to generate maps of six distinct brain networks. Network one, for instance, encompassed parts of the brain associated with reinforcement learning. Network four, on the other hand, included “higher-order cortical regions that may be involved in social action and interaction.”
The team found that anatomical variations in the dogs’ brain networks were associated with variations in their behavior. So breeds like golden retrievers, which were reared to visually track birds, displayed key distinctions in parts of the brain linked to “coordination, eye movement, and spatial navigation,” as Cara explains. Network two, which involved parts of the brain associated with smell and taste, “showed a significant correlation with scent hunting,” according to the study authors.
“Brain anatomy varies across dog breeds,” Hecht explains in an interview with Jason Bittel of the Washington Post, “and it appears that at least some of this variation is due to selective breeding for particular behaviors like hunting, herding and guarding.”
It is important to note—as the study authors do—that the new paper represents only some of the 202 dog breeds recognized by the American Kennel Club, and it is possible that a different sample makeup would have produced different patterns of brain variation. Also significant is the fact that all of the dogs involved in the new paper were household pets, and thus are not fulfilling the role for which they were originally bred. “[F]uture studies on purpose-bred dogs that are actively performing the tasks for which they are presumably adapted might expect to find additional or more pronounced neuroanatomical effects than we observed here,” the study authors write.
Moving forward, Hecht and her team hope to gain a better understanding of why dogs within the same breed display diverse behaviors: “For example, border collies who are winning herding competitions out in the real world,” she tells Bittel, “and siblings of those dogs who, for whatever reason, would rather just sit on the couch.”