Study links relative brain volume to temperament in diverse dog breeds

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Researchers from the University of Montpellier, the University of Zurich, Naturhistorisches Museum Bern, and other institutions have found that breed function and behavior correlate with relative endocranial volume (REV) in domestic dogs.

Domestic dogs exhibit variations of morphologies and cognitive abilities, a diversity rooted in centuries of domestication and selective breeding for functional attributes. Historically, mammals have shown a trend toward larger brains to support advanced cognition, a pattern that appears disrupted in domestic dogs.

Despite having, on average, 20% smaller brains relative to their wild ancestral counterpart, the gray wolf, domestic dogs often demonstrate a range of equivalent cognitive skills, challenging some conventional assumptions about brain size and intelligence.

In a study, "Breed function and behavior correlate with endocranial volume in domestic dogs," published in Biology Letters, the researchers used relative endocranial volume (REV) as a proxy for relative brain size and looked for correlations with dog breed, breed function, phylogenetic classification, cranial shape, and cooperative behavior as an indicator of social cognition and personality traits.

Using data from 1,682 dogs representing 172 breeds, researchers reveal that REV correlates very well with function, body size, phylogenetic clade, and cranial shape.

Researchers utilized a consistent method for measuring endocranial volumes across all sampled dogs, ensuring reliability in the data. By categorizing breeds based on traditional functions defined by the American Kennel Club and analyzing phylogenetic clades, the study provided a comprehensive overview of how historical and genetic factors influence brain morphology. Cranial shape, measured through the cranial index, showed a positive but weak correlation with REV, indicating that skull morphology alone is not a strong predictor of brain size.

REV was found to increase with fear, aggression, attention-seeking, and separation anxiety and to decrease with trainability.

Toy breeds, primarily bred for companionship, possess the largest relative brain sizes compared to their body mass.

Working breeds, selected for complex human-assistance tasks such as guarding, rescue, and policing, exhibit the smallest REVs. This inverse relationship suggests that the complexity of skills traditionally associated with higher cognition does not necessarily correspond to larger brain sizes in dogs, and cooperative behaviors showed no significant correlation with REV.

Behavioral traits were assessed using the Canine Behavioral Assessment and Research Questionnaire (C-BARQ), encompassing a range of temperaments from trainability to various forms of aggression and fear responses.

The significant correlations between REV and these behavioral traits, excluding cooperative behavior, show the intricate relationship between brain structure and behavior in domestic dogs and the evolutionary adaptability of mammalian brain size under domestication and artificial selection pressures.

More information: Ana M. Balcarcel et al, Breed function and behaviour correlate with endocranial volume in domestic dogs, Biology Letters (2024). DOI: 10.1098/rsbl.2024.0342

Journal information: Biology Letters

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