A study published in Royal Society Open Science finds that dog brain volume fell by about 46% by roughly 5,000 years ago, based on CT-based reconstructions of 207 skulls (including 22 prehistoric specimens). Early ancestral dogs had brain sizes similar to contemporary wolves, but later dogs were smaller in both brain and body size. Researchers suggest changes in human society and selection for docility likely contributed, though brain organization — not size alone — determines cognitive capacity.
Study Finds Dogs' Brains Shrank Nearly 50% During Domestication
Dogs’ brains shrank by around half at certain stages during their domestication, study says. Thomas Warnack/dpa
A new study in Royal Society Open Science reports that the brains of dogs decreased dramatically during parts of their domestication history, falling by roughly 46% by about 5,000 years ago. The research, led by Thomas Cucchi of the Muséum national d’Histoire naturelle (MNHN) in Paris, combines CT-based virtual reconstructions of skull cavities with a broad sample of modern and prehistoric specimens to trace changes in cranial capacity over time.
How the Study Was Done
The team examined 207 skulls in total: 185 from modern dogs, dingoes and wolves, and 22 prehistoric skulls, with the oldest specimens dating to about 35,000 years ago. Using CT scans, researchers produced virtual endocasts — digital impressions of the brain cavity — and used cavity volume in fossils as a proxy for brain size.
Key Findings
Early ancestral dogs from the Ice Age showed brain sizes comparable to contemporary wolves; one Belgian specimen even had a slightly larger internal skull volume. However, by about 5,000 years ago the average brain volume of dogs had dropped by nearly half (about 46%), leaving cranial capacities similar to those of many modern small terrier and miniature breeds. The researchers also found that these middle-period dogs were generally smaller in body size, with estimated shoulder heights of about 35–45 cm.
Why This Might Have Happened
The timing of the reduction coincides with major human cultural changes: as Central European populations shifted from mobile hunter-gatherer lifestyles to settled farming and livestock rearing, dogs’ roles changed. Dogs likely lived close to settlements as scavengers, worked as guards, assisted with herding, and in some contexts were used as food. The research team suggests that both ecological shifts and direct human selection — for calmer, more docile animals — could have contributed to reduced brain size. Similar, though smaller, trends have been observed in other domesticated species.
Caveats and Implications
Scientists caution that brain size alone does not determine intelligence. What matters more is how neural tissue is organized and wired. The study documents a striking change in cranial capacity but leaves open questions about the functional and behavioral consequences of that change. Further work is needed to link brain morphology with cognition and behavior in early domestic dogs.
Bottom line: The study provides robust fossil and modern-sample evidence that dogs underwent a substantial reduction in brain volume during domestication, likely tied to changing roles around humans and selective breeding for temperamental traits.
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