It has long been known that dogs have smaller brains than wolves, but new research suggests their brains began shrinking at least 5,000 years ago. Experts say the findings offer fresh insights into domestication, but a reduction in brain size does not mean dogs are less intelligent than their wolf ancestors.
Brain Size Reduction Over Time
Researchers led by Dr. Thomas Cucchi from the French National Centre for Scientific Research studied CT scans of skulls from 22 prehistoric wolves and dogs dating back 35,000 to 5,000 years, along with scans from 59 modern wolves and 104 modern dogs, including various breeds, stray dogs, and dingoes. The results, published in Royal Society Open Science, show that modern dog breeds, dingoes, village dogs, and Late Neolithic dogs have brains 32% smaller than ancient and modern wolves. Specifically, Late Neolithic dogs (around 5,000 to 4,500 years ago) had brains 46% smaller than wolves from the same period, similar in size to modern pugs. This difference persisted even when accounting for body size.
No Brain Shrinkage in Early Domestication
Interestingly, two ancient canines that lived alongside humans 35,000 and 15,000 years ago—sometimes called “protodogs”—did not show smaller brains than wolves. One even had a relatively larger brain, suggesting brain size may have increased in early domestication stages. This challenges the idea that brain shrinkage is an early hallmark of domestication.
Why Smaller Brains?
Dr. Cucchi noted that the reasons for brain shrinkage remain unclear. Some research indicates that smaller brains reorganize, making dogs less trainable and more wary of environmental changes, which could be useful as “alarm systems.” Alternatively, limited food resources in Neolithic villages may have favored smaller dogs with smaller brains, which require less energy.
“The way our dogs live nowadays doesn’t give them the opportunity to always express most of their intelligence,” Cucchi said. “But they are extremely clever and domestication didn’t make them stupid, but made them really capable of reading us and communicating with us.”
Expert Reactions
Dr. Juliane Kaminski, an expert in canine cognition at the University of Portsmouth who was not involved in the study, highlighted that “protodogs” did not have smaller brains than wolves. “They didn’t yet show this sign of domestication that we thought is a standard part of this domestication syndrome,” she said. Kaminski added that the study suggests the human-dog bond may have started loosely before becoming very strong, with full domestication syndrome appearing later than genetic data suggests.
