Which makes a border collie instinctively adapted to herding sheep, a German Shepherd perfect for police work, or a superb beagle for following a scent? Since the domestication of a Pleistocene wolf some 14,000 years or more ago, humans have played a decisive role in the evolution of the dog. First bred for taming, dogs have since been selected to perform many specialized tasks, such as showing prey or guiding the blind. Could the study of modern dog breeds shed light on how brains evolve in response to selection pressure on behavior?
Erin Hecht, assistant professor in the department of human evolutionary biology, questioned whether adaptations and specialized behavioral abilities of races could be seen as neuroanatomical changes. When she compared MRI scans of 62 purebred dogs from 33 unique breeds, she found some notable differences.
The specialized behavioral adaptations and abilities of dog breeds are clearly visible in the form of neuroanatomical changes.
In fact, she discovered six networks of brain regions that covary (change together), each associated with reproduction for specific behaviors, such as sight hunting, scent hunting, guarding, and companionship. For example, in dogs that hunt by sight, she found differences in a network of brain regions involved in visual perception and navigation. “We think,” she says, “it could be related to visually tracking a bird or whatever the dog is following.” Dogs’ skulls come in all shapes and sizes: some are large, some are long and narrow, and some are very small. But Hecht found that while brain size, body size, and skull shape influence brain anatomy, there are additional neuroanatomical differences between races as well. in addition to these factors.
Hecht and his colleagues published these results in the Journal of Neuroscience last September, accompanied by a phylogenetic analysis of the genealogical tree of modern canine breeds. This established that differences in brain structure between races could not be explained by deep ancestry. Instead, in separate branches of the tree, the selection pressure for specific behavioral traits, possibly over the past 200 years, has led to the simultaneous emergence of particular networks of brain structures. Thus, scent dogs from different branches of the family tree shared similar anatomical differences. .
Hecht first became interested in studying brain evolution in canines when she discovered a well-known experiment in Siberia to breed wild silver foxes to either become tame or aggressive. Since 1959, the most tame foxes – initially selected for the distance they would allow a human to approach before running away – have been studied in Novosibirsk, to find out whether selection for taming may also have resulted in traits such as floppy ears, wavy hair, and curly or shortened tails shared by many domesticated breeds. Sixty years after the experiment began, Hecht says, the most tame foxes now respond to people by wagging their tails. “They lick, moan and seem delighted at the prospect of human contact.”
But surprisingly, little research had studied the changes in their brains like the work of Hecht and Christina Rogers Flattery, a postdoctoral fellow in Hecht’s lab, is currently doing. Having established that changes in dog behavior are linked to changes in neuroanatomy, the Hecht lab began studying the brains of these domesticated foxes to see what human first selection pressure on a dog looks like. “The regions of the brain that we see involved in this selection for taming are found in the limbic system and the prefrontal cortex,” Hecht explains. “The limbic system governs instinctive emotional responses, the fight-or-flight response, and aspects of social behavior that are signaled by odors, while the prefrontal cortex regulates types of voluntary behavior, as well as more complex aspects of behavior. social such as interpreting social signals and deciding what types of social signals to send back. This is where we see changes so far in foxes.
Oddly, however, in the brains of dogs, the morphologies related to taming are not as clearly discernible, and Hecht says that ongoing behavioral study suggests that dogs are not as friendly as tame foxes. First-year doctoral student Sophie Barton says she was “completely shocked by this – we expected the dogs to run to the front of the cage … when a stranger entered …, but instead of this, they took a wait-and-see approach, acting neither aggressive nor friendly until they could discern the human’s intentions. Barton believes the difference may have evolved due to the fact that dogs have lived in a complex human environment and with very different selection pressures over the past 200 years of intensive breeding. Although taming is an important part of the initial stage of domestication, she says, the trait “can certainly be manipulated in later stages.”
Hecht and Barton are particularly interested in what these studies may reveal about brain plasticity: how innate adaptations for a particular skill interact with acquired experience to shape neuroanatomy. The human brain, for example, has adaptations for acquiring language that are activated when listening to other people speak. A similar “experience-expected plasticity” underlies skill behavior in working dogs, Barton explains. On the lab’s project website, caninebrains.org, she recruits dogs from both working (shepherds and livestock keepers) and hunting (retrievers, flushers and pointers) breeds with does not work siblings, to study neural changes caused by training and experience.
“We know training does something,” says Hecht. “We’re trying to figure out how far an innate genetic inheritance takes you. And then, what’s the extra bump you would get from experience and learning? Along with working with humans, she and fellow postdoctoral researcher Suhas Vijayakumar are tracking how the brains change as people learn Paleolithic tool-making skills, crucial for much of evolutionary history. human, and compare these changes to brain changes seen in undergraduates learning computer programming. .
For now, Hecht and Barton hope to make the dog a model for evolutionary neuroscience, to learn how structures in the brain change and how the brain balances innate adaptations with propensities for plasticity. “I think a lot of questions can be answered with these animals,” Barton explains, “because we know what selection pressures they went through to develop various skills and different types of behaviors. Ultimately, the brains of dogs can reveal just as much about the brains of their owners.