News release

From: The Royal Society

Brain size reduction in dogs was already established at least by the Late Neolithic of western Europe, 5,000 years ago.

Why did domestic dogs’ brains shrink over time? New research reveals surprising clues. By analyzing endocasts of 185 modern and 22 prehistoric wolves and dogs—spanning 35,000 years—scientists found that early “protodogs” from the Pleistocene era had *larger* brains than their wolf counterparts, hinting at greater behavioral adaptability near humans. However, by the Late Neolithic (5,000 years ago), dogs experienced a dramatic 46% brain size reduction, comparable to today’s small terrier breeds. This shrinkage may have reshaped their temperaments, making them more alert and wary—traits that could have been valuable in ancient human societies. The study sheds light on how domestication transformed dogs’ brains and roles alongside humans.

Brain drain - Dog brain size fell dramatically around 5,000 years ago, dropping by around 46% compared with wolves. Earlier “protodogs” - intermediate canines that existed between wolves and domestic dogs - show no evidence of brain shrinkage, and brain size slightly increased initially as dogs began to interact more closely with humans. The later sharp reduction, with brain volumes similar to modern Toy breeds, points to very early behavioural selection during domestication, the authors said