The conclusion of a recent study to identify the most and least aggressive common dog breeds at the University of Pennsylvania claims that little dogs such as Chihuahuas and Dachshunds tend to be feisty, while certain breeds, like Golden and Labrador Retrievers, are as mellow as their reputations suggest. The study is one of the most extensive of its kind and is the first to report aggression related to breed. Although certain pooches appear to be more cantankerous than others, Chihuahuas and Dachshunds scored higher than average for aggression directed to both humans and dogs, putting them towards the top of the list. "Small size very likely plays a large role in the development of fear-based aggression among some breeds. Smaller dogs may feel more threatened by other dogs and people -- a perception that may be well founded.” The study goes on to say: "There is some evidence that smaller breeds are more often the targets of aggression by other dogs. And small breeds, particularly Dachshunds, are more prone to injury due to rough handling by children, so this form of aggression among small breeds may be a learned response due to negative past experiences." Akitas and Pit Bull Terriers, which have "bad boy" reputations, mostly scored high for dog-directed aggression. When they did injure humans, however, the injuries tended to be more severe than those inflicted by the scrappy, smaller dogs. Other breeds with a greater tendency to bite humans included Jack Russell Terriers, Australian Cattle Dogs, American Cocker Spaniels and Beagles.On the "least aggressive" end of the spectrum were Basset Hounds, Golden Retrievers, Labrador Retrievers, Siberian Huskies, Bernese Mountain Dogs, Brittany Spaniels, Greyhounds and Whippets. Interestingly enough, several of these dogs also rated low for "watchdog behaviour" and "territorial defence" behaviours, suggesting that they tend to be lovable family pets, but are less vigilant watchdogs than Chihuahuas and Dachshunds. Having a tough appearance, however, can make up for a lack of skill. "Certain breeds, through either their reputation or their size, are inherently more intimidating than others even if they show little or no aggressive behaviour," it is further reported. The researcher’s advice which I totally agree with is this: “Anyone looking to bring a dog into their home should find out as much as possible about the individual dog's history and temperament. Certainly some breeds are better with children than others on average. However, it wouldn't make sense to pass up a well-socialized, well-trained, non-aggressive Rottweiler for an atypically aggressive Labrador Retriever."