A lot of this is due to the differences in behavior Campbell says is related to breed. "Pit bulls are bred to fight" Campbell said "in the same way retrievers are bred to retrieve." While many of us know pits we adore, Campbell says the instinct to attack is in the breed's nature the same way herding is in even the most urban sheepdog's DNA.
That's Deb Campbell, San Francisco Animal Care and Control's spokesperson who is also apparently a canine geneticist. The first, by the way, to discover the "attack instinct" gene. Color me impressed.
Campbell is not a breed expert. She was a volunteer coordinator at the shelter and apparently she's also their spokesperson. For Pit Bulls, it's a bit like an unrepentant drunk driver being the spokesperson for MADD.
Not all Pit Bulls are bred to fight. I'd wager most are not. Most are bred to produce puppies for people to sell at a cheap price for profit. Most Retrievers are not bred to retrieve, most are bred to produce puppies for people to buy.
True fact: Very few dogs are bred to perform their original function.
There is not a genetic marker known to experts that, when knocked-out, eliminates the "instinct to attack". Aggression is not a single-variable trait, there is not a 1:1 ratio between gene expressed and attack behavior. People still debate some of the more nuanced expression of coat color, and aggressive behavior is far more complex.
Which is why, if you are a spokesperson for an agency that is supposed to protect animals, you should not espouse lies as if they were truth. It is a huge disservice to an already exploited and discriminated against dog and their guardians.