SCIENTISTS FINDS THAT THE SMARTEST DOGS HAVE THE SMALLEST BRAINS
It's a common misconception that intelligence increases with brain size. Scientists have long been baffled by the human brain, but a recent study discovered the unexpected opposite in our canine companions. According to a startling study published in the journal Biology Letters, "smarter" dogs—specifically, working breeds that are renowned for their capacity to carry out difficult tasks and support people have the smallest brains in relation to their body size. On the other hand, companion breeds like chihuahuas and toy dogs typically have the largest relative brain sizes.
Using samples from Switzerland's Natural History Museum Bern, researchers from France and Switzerland studied the skulls of 1,682 adult dogs of 172 different breeds. As a measure of cognitive ability, they took the dogs' relative endocranial volume (REV), or the size of the brain in relation to the body. Using results from the Canine Behavioral Assessment and Research Questionnaire, which assesses characteristics like aggression, trainability, and attention-seeking, the researchers also examined breed function, cranial shape, cooperative behaviour, and temperament.
The results cast doubt on the evolutionary-based presumption that higher cognitive capacities are associated with larger brains. The fact that working dog breeds have the smallest endocranial volumes in relation to their body size indicates that brain size alone cannot be the deciding factor. As evidenced by studies that relate variations in brain structure to particular breed functions like hunting, companionship, or guarding, internal brain composition and organisation have a greater impact.
The study demonstrates the relationship between REV and behaviour, demonstrating how selective breeding and domestication can affect mammalian brain size in response to particular human-selected traits. For instance, characteristics like fear and aggression raise REV.
Additionally, studies have shown that toy breeds with larger relative brain sizes, such as Yorkshire terriers, pugs, and chihuahuas, frequently exhibit higher levels of aggression, fear, separation anxiety, and attention-seeking behaviours. Because these characteristics made the dogs more loving and attention-seeking—qualities perfect for companionship—they were favoured in selective breeding. On the other hand, such behaviours would be rather detrimental in working dogs that are bred for trainability, a trait associated with smaller REV size.
The study's lead author, Ana Baracel, an evolutionary biologist at the Montpellier Institute of Evolutionary Sciences, stated, "We can say that we have really altered the brains—not just the body sizes and proportions of different dogs, but it looks like we have also changed their brains in a significant way."
