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As many dog owners can attest, their four-legged companions are delightful and loving. But for others, their animals have an aggressive side, such as biting and attacking strangers, which may ultimately lead to them having to be euthanized. But why do some dogs turn out this way?

According to a new study of 211 dog breeds in the journal Scientific Reports, adverse experiences such as abuse or being given up during a dog's first six months of life mean they are more likely to be fearful and aggressive as adults.

To explore this link between early life experiences and adult behavior, scientists conducted a large-scale survey of 4,497 dog owners. Each owner filled out a detailed questionnaire about their canine companion, including its complete life history, breed and current living environment. They were also asked about any adversity their pet experienced during its first six months.

Additionally, owners completed a standard behavior test (C-BARQ) to rate their dog's current fear and aggression levels. The scientists then used powerful statistical tools to determine whether early trauma, breed, or a combination of the two was most responsible for a dog's behavior.

Nature and nurture

Just like in humans, the first few months of life are crucial for emotional development. The research team found that dogs that experienced any kind of adversity in the first six months were more likely to be aggressive as adults, regardless of age or sex or whether the animal was neutered. Both genes and environment are involved, as indicated by the fact that the effect of adversity differed across different breeds.

For example, some breeds, such as Siberian Huskies, American Eskimo Dogs, and American Leopard Hounds, as well as pit-bull type dogs, were more likely to become aggressive or fearful after experiencing early trauma. Meanwhile, other breeds, such as the Labrador Retriever, were a lot more resilient. Even when they experienced trauma, the chances of them being aggressive adults were relatively low.

"Our findings establish that breed ancestry and individual experience interact to show fear and aggressive behavior in pet dogs, confirming that socioemotional behavior is shaped by gene-environment interactions," wrote the researchers in their paper.

Overall, the study clearly demonstrates that a dog's early life is crucial and highlights the importance of responsible breeding and proper pet care. A next step for scientists could be genetic studies to identify specific genes linked to problematic behaviors and resilience, which could help inform breeding programs and improve canine welfare.