The seemingly sweet-natured English cocker spaniel may be the world's most aggressive dog breed, according to a new study published in the Journal of Veterinary Behavior.

For the study, researchers at Spain's School of Veterinary Medicine at the Autonomous University of Barcelona crunched data related to more than 1,000 dog aggression cases logged at an area veterinary teaching hospital during the period of 1998-2006.

Of those cases, English cockers ranked the worst, followed by Rottweilers, boxers, Yorkshire terriers and German shepherd dogs. Discovery News has the details:

Probing the data further, [the study's lead author, Marta Amat] and her team discovered that English cocker spaniels were more likely than other dogs to act aggressively toward their owners as well as unfamiliar people. In contrast, dogs with reported behavior problems from other breeds tended to act aggressively toward other dogs. Among the English cocker spaniels, golden varieties and males were found to be the most hostile. ...

In terms of coat color, Amat explained that the coat pigment melanin shares a common biochemical pathway with dopamine and other brain chemicals involved in the control of aggressive behavior.

The results of the study mirror the findings of an earlier research team, also from Spain, conducted by scientists at the University of Cordoba. That study also found that male and golden-colored English cockers had a higher incidence of aggressive behavior than females or English cockers with other coat colors.