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What factors predict aggressiveness in dogs?

For a long time, scientists have used to associate dogs’ aggressiveness solely with breed. However, a paradigm shift has occurred over the past decade, due to research linking behavioral profiles to factors such as dogs’ sex, age, metabolism, and hormonal patterns. 

Now, based on a survey of 665 dog owners detailing the physical and behavioral features of their pet dogs, a team of researchers led by the University of São Paulo (USP) in Brazil has investigated how morphological, environmental, and social factors modulate canine aggressiveness.

The scientists found that aggressiveness was influenced both by physical traits such as weight and skull morphology, and by social and environmental factors like the type of household the dogs lived in, the animals’ life histories, and the owner’s gender and age. These findings confirmed the hypothesis that behavior is not only learned or influenced by genetics but also the outcome of interactions with the environment.

“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 study senior author Briseida de Resende, a professor of Psychology at USP.

“The owner’s gender was found to be a good predictor of behavior toward strangers, in that absence of aggressiveness was 73 percent more frequent among women’s dogs,” reported lead author Flávio Ayrosa, a psychologist at the same university. 

Moreover, the dogs’ sex and snout characteristics also appeared to influence their aggressiveness. “The likelihood of aggressive behavior toward the owner was 40 percent lower among female dogs than among males,” Ayrosa said. 

“Snout length was even more significant: aggressiveness toward the owner was 79 percent more likely among brachycephalic [dogs with short snouts] than mesocephalic dogs [characterized by a longer snout].” 

In addition, the researchers also discovered that the heavier the dog, the less likely it was to display aggressiveness toward its owner, with aggressive behavior decreasing by three percent per extra kilogram of body mass.

However, the scientists stressed that the owner-related findings are not necessarily cause-and-effect correlations. 

“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,” Ayrosa explained. 

“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.” 

The study is published in the journal Applied Animal Behavior Science.

By Andrei Ionescu, Staff Writer

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