In a recent report in the Herald Sun, Dr. Robert Holmes, an animal psychologist, maintained there are 3 qualities that influence the level of aggression displayed by a dog. Genetic makeup and breeding was one quality, to be balanced by the dog s environment and its experiences. He was strongly influenced by the works of Charles Darwin, who argued that evolution results from selection. Followers of this belief conducted laboratory research that showed animals could be selectively bred to show elevated levels of aggressive behaviour. For this reason, some believe that animal aggression could be a biological imperative.
Biological determinants can include damage to the brain and abnormal levels of hormones.
Certain breeds have attracted much attention for their genetic tendency toward aggression. The pit bull terrier has been the target of controversy in the U.S.A. since the mid-1980s. They concluded that a long history of breeding for fighting has given pit bulls a genetic predisposition for abnormal aggressiveness. Lockwood stated, Their behaviour is totally abnormal in an evolutionary or ecological sense and is strictly the result of human intervention. A dog that attempts to avoid fights by fleeing may actually cause an attack.