The surprising impact of domestication on the brains of dogs: what science reveals about their evolution
These findings underscore that the relative size of the brain is not the only determinant of cognitive sophistication, and that functional specialization plays a crucial role in the evolution of dogs' brains.
A new study published in the journal Biology Letters unravels the effect of domestication on the size and structure of dogs' brains, revealing key differences between breeds and functions. According to the research, small companion dogs have a relative endocranial volume (REV) that is higher than that of large working breeds, a finding that challenges traditional ideas about intelligence and brain size.
How Domestication Transformed Dogs' Brains
The bond between dogs and humans has deep roots, dating back thousands of years when wolves began to interact with human communities. This approach marked the beginning of a domestication process that transformed not only their behavior but also their biology, leaving a significant mark on the size and structure of their brains.
For centuries, dog breeds were selected for specific purposes: from hunting and herding to simple companionship. This directed selection resulted in an impressive diversity in their shapes, sizes, and cognitive abilities. But how did this process influence the brains of canines?
The Study That Changed Our View on Canine Brains
A team of researchers from the University of Montpellier, the University of Zurich, and the Bern Natural History Museum analyzed data from 1,682 dogs of 172 different breeds to study the impact of domestication on their brains. The scientists focused on the relative endocranial volume (REV), a measure of brain size in relation to body size, and how it varies according to the functions of the breeds.
What is Relative Endocranial Volume?
REV is used as an indicator of brain size in relation to body mass. According to the study, small breeds raised as pets have a significantly higher REV than working breeds, such as German shepherds or Labradors, selected for complex tasks like rescues or herding.
This result poses an interesting paradox: while working breeds perform tasks that require advanced cognitive skills, their relative brain size is smaller than that of breeds designed for companionship.
Why Do Small Dogs Have Larger Brains in Proportion to Their Bodies?
Small breeds, such as Chihuahuas and Bichons, were bred to interact closely with humans, which may have required specific brain adaptations to enhance communication and coexistence. This finding highlights the influence of domestication on the restructuring of their brains.
On the other hand, working breeds, although they have larger absolute brains, exhibit a lower REV. This suggests that their specialization in specific skills, such as herding or guarding, does not necessarily depend on the relative size of the brain.
Comparison Between Dogs and Wolves: What Does Brain Size Say?
Gray wolves, the ancestors of dogs, have brains that are 20% larger than their domesticated descendants. At first glance, this might seem indicative of greater cognitive capacity, but dogs have developed a wide range of skills comparable to those of wolves, such as problem-solving and social understanding.
The study links this brain reduction to the evolutionary pressures faced by wolves as they adapted to life near humans. The dependence of dogs on human resources and protection reduced the need for skills like hunting, resulting in changes in their brain structures, a phenomenon known as the domestication effect.
Skills That Replace Size
Although dogs' brains are smaller, they have reorganized to meet the demands of human coexistence. Skills such as cooperation, communication, and obedience seem to have taken priority in their cognitive evolution.
How the Study Was Conducted
To reach these conclusions, the researchers employed a comprehensive approach that included precise measurements of endocranial volume using imaging techniques. They also categorized breeds according to traditional functions established by the American Kennel Club, such as work, companionship, hunting, and herding.
Additionally, the study evaluated physical characteristics such as skull shape through cranial index, although it was found that the relationship between skull shape and REV is weak, suggesting that other factors have greater influence.
Relationship Between Brain and Behavior
Scientists also used tools like the C-BARQ (Canine Behavioral Assessment and Research Questionnaire) to study the relationship between brain size and behavioral characteristics such as aggression, fear, and separation anxiety.
Interestingly, breeds with higher REV showed tendencies toward behaviors like fear and anxiety, while breeds with high trainability had a lower REV. This calls into question the idea that a larger brain equates to greater intelligence.
What Does This Tell Us About Dog Evolution?
The study demonstrates that domestication not only shaped the external appearance of dogs but also their cognitive and emotional capacities. Skills related to communication and obedience, fundamental for coexisting with humans, seem to have been favored over thousands of years.