Nature versus nurture regarding aggression in specific dog breeds
It seems that there are some important differences in dog aggression depending on the dog breed (towards strangers, owners, and other dogs):



That being said, it seems that a significant proportion of a dog's behavior can be due to its environment (training, etc), according to a study, this 'nurture' component might explain up to 80% in the variation in aggression (which should be considered when interpreting the other study I cite).