Research Finds Dogs' Aggressiveness Is Influenced By Their Life History And Owners

A study by researchers at the University of São Paulo (USP) in Brazil found that dog behavior is influenced by genetics and constant interaction with the environment.

The study included 665 pet dogs of various breeds as well as mongrels. Several findings were made, including that dogs walked daily by their owners are less aggressive, and dogs owned by women bark less at strangers. Heavier dogs are less likely to be disobedient than lighter pets. Pugs, Bulldogs, Shih Tzus, and other short-snouted breeds may misbehave more than medium- and long-snouted breeds like Golden Retrievers or the caramel-colored mixed-breed dogs popular in Brazil.

"The results highlight something we've been studying for some time: behavior emerges from interaction between the animal and its context. The environment and the owner-pet relationship, as well as morphology, are all factors that influence how pets interact with us and how we interact with them," said Briseida de Resende, professor at the Institute of Psychology (IP-USP).

The owners of the 665 dogs in the study completed three online questionnaires on themselves, the characteristics of their pets, the environment they lived in, and any aggressive behavior, such as barking at or attacking strangers. Natália Albuquerque, an IP-USP researcher, and Carine Savalli, a Federal University of São Paulo (UNIFESP), created the questionnaires.

"The owner's gender was found to be a good predictor of behavior toward strangers, in that absence of aggressiveness was 73% more frequent among women's dogs," said Flávio Ayrosa, one of the authors.

The gender of the pet appears to have influenced aggressiveness as well. Female dogs were 40% less likely than males to exhibit aggressive behavior toward their owners. Another finding was that aggressiveness toward the owner was 79% more likely in brachycephalic dogs than in mesocephalic dogs, indicating that snout length is an essential factor.

The study also discovered that the larger the dog, the less likely it was to be aggressive toward its owner. The likelihood of aggressive behavior decreased by 3% for every additional kilogram of body mass.

Ayrosa emphasized that the owner-related findings are not cause-and-effect relationships.

"We found relationships, but it's impossible to say which comes first. In the case of the factor 'walking the dog,' for example, it may be that people walked their dog less because the animal was aggressive, or the dog may have become aggressive because the owner didn't take it out enough," he said.

"Traits such as weight, height, cranial morphology, sex and age influence the interaction between dogs and their environment. They may spend more time inside the home because of them, for example."

Canine aggressiveness was previously associated solely with the breed, but there has been a paradigm shift in the last ten years due to research linking behavioral profiles to factors such as the dog's age and sex, as well as its metabolism and hormones.

The IP-USP study was the first in Brazil to examine morphology and behavior in mongrels or dogs of unknown breeds, including aggression.

"Researchers have only recently begun to investigate the influence of factors relating to the animal's morphology, life history and origin [purchased or adopted], as well as characteristics of the owner, as our study did," stated Ayrosa.