A study of purebred dogs claims to reveal the factors that make a canine companion more likely to be aggressive – including size, breed, sex, age, and environmental influences. Among other things, the findings suggest we may be fearing the wrong breeds. Moreover, although breeding plays a part, it looks to be among the less important factors in measuring whether a dog presents a danger.
Professor Hannes Lohi of the University of Helsinki surveyed thousands of Finnish dog-owners about the aggressiveness of their pets towards humans, as measured by biting or frequent growling. Out of 9,270 useable descriptions, 1,791 (19.3 percent) met the criteria for high aggression. In Scientific Reports, the study claims owner responses are an accurate way to measure aggression, but it seems credible that the owners of some dogs might be more reluctant to admit to some bad behavior than others. In particular, those who keep breeds frequently described as dangerous might not want to admit their hound fits the stereotype.
Assuming Lohi's dataset is accurate, however, some quite clear patterns emerge. For one thing, aggression increases with age, and male dogs are 72 more percent likely than female ones to show aggression.
Environmental factors also count; the first dog someone has owned is more often aggressive than later ones, indicating people's dog-handling skills improve with time. Only dogs are 23 percent more likely to display aggression to humans than those living with others of their kind, although the authors are unsure if this is because people don't get companions for dogs they think might attack them.
A Napoleon complex – whether real or myth in humans – exists in dogs. The paper finds small dogs are 49 percent more likely to be aggressive than large ones, and 38 percent more so than medium-sized dogs. The difference between large and medium was not statistically significant.
Perhaps this is explained by small dogs simply having more reason to be afraid, because Lohi found an animal's fearfulness by far the best predictor of whether it would display aggression to humans.
“One of the potential reasons behind this can be pain caused by a disease. Impairment of the senses can contribute to making it more difficult to notice people approaching, and dogs' responses to sudden situations can be aggressive," first author Salla Mikkola said in a statement.
Results for breeds were much less clear. Past research has found chihuahuas and Jack Russells are particularly aggressive, but Lohi reports they actually come out as less aggressive than most once body size is taken into account. Rough collies, miniature poodles, and miniature schnauzers came out on top in the ranking of aggressive breeds in this study. On the other hand, it seems Labradors and Golden Retrievers deserve their placid reputations, with lower reported aggression than other breeds. Staffordshire Bull Terriers – which some countries consider so dangerous they have made them a restricted breed – actually fell below the average for aggressiveness according to the owner reports, although they might be particularly damaging if they did decide to attack.
Lohi presents these results as a way to select for less aggressive dogs (although how one deals with changes with age is unanswered). However, this may reveal altogether too much optimism about owners' preferences. One study found young people who are score high for disagreeableness on personality tests have a preference for more aggressive dogs, which probably isn't all that surprising.