Dogs Brains Today Are Undergoing a Mysterious Expansion, Study

A wolf and a Golden Retriever of identical body weight share almost nothing when it comes to their brains. According to a 2023 study in the journal Evolution, wolves average around 131 cubic centimeters of brain volume. Dogs of a similar weight come in at roughly three-quarters of that. That gap has been the accepted story of domestication for decades: when wolves became dogs, they traded cognitive horsepower for companionship. But something unexpected has been happening inside the skulls of modern breeds – a reversal nobody fully predicted, and one that researchers are still trying to explain.

Modern dog breeds that are genetically more distant from wolves have a relatively larger brain size compared to ancient breeds that are thousands of years old, and the increase cannot be attributed to the roles or life history characteristics of the breeds – suggesting it is likely influenced by urbanization and a more complex social environment. That finding, counterintuitive on its face, marks a sharp departure from what biologists expected to find when they looked at brain evolution in domesticated animals.

The conventional wisdom had always been that domestication shrinks brains. Remove a species from the pressures of surviving in the wild – navigating predators, finding food, competing for mates – and natural selection stops rewarding neural investment. The brain is metabolically expensive, so without the survival pressure to justify that cost, it gets smaller. Dogs fit that model almost perfectly, right up until the modern breeding era, when the data started telling a different story. The dog brain expansion currently underway in modern breeds doesn’t fit the old template, and several research teams have now spent years trying to understand why.

What the CT Scans Revealed About Dog Brain Expansion

Researchers behind the 2023 Evolution study used a novel endocranial dataset based on high-resolution CT scans to estimate brain size in 159 dog breeds. Data was gathered from 865 individuals representing 159 dog breeds, with 48 specimens representing wolves – among the most comprehensive canine neuroanatomical surveys ever conducted. The results challenged a foundational assumption in the study of domestication.

Behavioral differences may appear substantial between functional breed categories such as toy dogs and sporting dogs, but these differences are apparently not large enough to affect relative brain size. Whether a breed was developed to retrieve birds or sit in a lap doesn’t explain why its brain is bigger. The answer seems to lie elsewhere – in the social and environmental pressures that all modern breeds now share.

Enikő Kubinyi, a professor and head of the Department of Ethology at ELTE Eötvös Loránd University, put it plainly: “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 kind of hobby. The results show that the breeding of modern dog breeds has been accompanied by an increase in brain size compared to ancient breeds. We couldn’t explain this based on the tasks or life history characteristics of the breeds, so we can only speculate about the reasons.”

The Long Shadow of Domestication

Domestication has long been considered the most powerful evolutionary engine behind dramatic reductions in brain size in several taxa, and the dog is considered a typical example of a substantial decrease in brain size relative to its ancestor, the grey wolf.

The dog was domesticated from the grey wolf, with genetic evidence placing that split at least 15,000 years ago. By the time humans were building early farming settlements, the brain reduction was already locked in. Using endocast volume – the internal volume of the skull – as a proxy for brain size, a 2026 study published in Royal Society Open Science compared endocranial volumes of ancient and modern wolves and dogs spanning from 35,000 years ago to the Late Neolithic period. Late Neolithic dogs show a drastic brain size reduction compared to wolves, with endocranial volumes comparable to modern small terrier and similar small breeds – a reduction of roughly 46% by around 5,000 years ago.

That shrinkage was established long before anyone was deliberately breeding dogs for specific traits. The Royal Society Open Science research confirmed that brain size reduction in dogs was already established at least by the Late Neolithic of Western Europe, 5,000 years ago – though the authors note that further samples from the Palaeolithic and Mesolithic periods are needed to fully test those conclusions.

Then came the second chapter: the last 200 years of intensive selective breeding. Most modern Western breed dogs possess highly derived physical and behavioral traits because of intense artificial selection for appearance and function within the past 200 years. In contrast, premodern dogs – including primitive and ancient breeds, village dogs, and New Guinea Singing Dogs – have undergone less intensive artificial selection and retain more ancestral characteristics. It’s this split, between modern and premodern dogs, that a 2025 study in the Journal of Neuroscience specifically set out to probe.

A Brain Rewired for Living With Us

Researchers conducted a voxel-based morphometry analysis – a technique that measures regional differences in brain tissue volume – using structural MRI images from 72 modern breed dogs and 13 premodern dogs, for a total sample of 85 animals. That’s a relatively small sample, and the authors themselves acknowledge that findings should be interpreted cautiously until replicated at larger scale. Still, the patterns that emerged were consistent across the group.

Modern breeds show cortical expansion associated with trainability, while premodern dogs exhibit relatively larger subcortical regions, notably the amygdala, linked to fear-related behavior. The amygdala is the brain’s threat-detection center, tightly connected to the fear response. Ancient dog lineages, whose neural architecture still resembles something closer to the wolf, show more of it. Modern breeds show less.

Cortical areas supporting social cognition and social communication are larger in modern dogs after controlling for overall brain size, while modern breeds have reduced amygdala volume, associated with lower fear scores. The behavioral implications of that pattern are tangible: a dog with a larger cortex and smaller amygdala is, on average, more trainable and less fearful – exactly what a dog needs to function well in a busy human household.

The brain appears to carry the imprint of two distinct selection pressures: the initial domestication from wolf, and then the deliberate and rapid breeding that followed the industrial revolution. Anthropogenic environments – urbanized, structured, rule-governed – seem to have driven the second wave of change.

For dog owners curious about how their own pet’s breed compares in terms of trainability and behavioral tendencies, research on the smartest dog breeds offers a useful lens into how these neurological differences show up in everyday behavior.

What’s Driving the Expansion?

The increase in brain size is not related to the specific roles or life history characteristics of the breeds, suggesting it is likely influenced by urbanization and a more complex social environment. Breed function – whether a dog was developed for sport, herding, guarding, or companionship – doesn’t predict relative brain size. Litter size doesn’t predict it either. Longevity doesn’t predict it.

What does predict it is genetic distance from wolves. The further a breed has moved from its wolf ancestry, the larger its brain tends to be relative to body size. That pattern points toward something broader than breed-specific selection pressures.

As Kubinyi has speculated, perhaps the more complex social environment, urbanization, and adaptation to more rules and expectations have caused this change, affecting all modern breeds. Urban dogs navigate traffic, strangers, tight apartments, leash laws, vet visits, and an enormous volume of human communication. Breeds that have lived in that world for generations may be under selection pressure – however subtle – that rewards the neural architecture needed to cope with it.

This idea connects to what evolutionary biologists call the social brain hypothesis: the idea that living in complex social groups is itself a driver of brain growth, because managing relationships, reading intentions, and cooperating with others requires more neural hardware. Recent neuroimaging, genetic, and comparative anatomical studies point to convergent changes in dogs and humans, including reductions in subcortical structures linked to aggressiveness and expansions of cortical regions supporting social cognition and executive functions. Dogs and their owners, it turns out, may have been shaping each other’s brains for a very long time.

Read More: Scientists Believe Dogs Are Entering a New Phase In Their Evolution

What This Means for You

The dog brain expansion story has practical relevance for anyone who lives and works with dogs. The 2025 Journal of Neuroscience research suggests that recent artificial selection has targeted higher-order brain regions in modern breed dogs, perhaps to facilitate behavioral flexibility and close interaction with humans. If you have a modern breed, you likely have a dog with a cortex tuned for learning, cooperation, and reading human signals – and that brain benefits from being used.

Training, socialization, and mental stimulation aren’t extras for dogs with this kind of neural architecture: they’re necessities. A dog whose higher-order cortical regions have been selected for interaction with humans will, without sufficient engagement, often redirect that capacity in less welcome directions. The evidence suggests that intensive selection in modern breeds has favored increased trainability and reduced fearfulness, which fits well with modern dogs’ role as companions coping with life in cities and as working animals solving complex tasks.

On the other side of the spectrum, if you own or work with a premodern breed – a Basenji, an Afghan Hound, a Shiba Inu, or a New Guinea Singing Dog – understanding that these animals carry a different neural profile can reframe frustrating moments in training. Their larger amygdala, linked to heightened fear responses, means they may need more patient desensitization rather than repetitive command training. The brain they have wasn’t built for the same kind of human-oriented compliance that a Border Collie’s was.

The precise mechanisms driving cortical expansion – whether epigenetics, specific gene variants, or cumulative environmental pressures across generations – remain open questions for future research with larger samples. But the shape of the finding is already clear: the dog sitting on your couch is carrying a brain that modern life helped build. And it’s still changing.

Disclaimer: This information is not intended to be a substitute for professional medical advice, diagnosis, or treatment and is for information only. Always seek the advice of your physician or another qualified health provider with any questions about your medical condition and/or current medication. Do not disregard professional medical advice or delay seeking advice or treatment because of something you have read here.

AI Disclaimer: This article was created with the assistance of AI tools and reviewed by a human editor.