Are Pit bull type dogs more aggressive?

The claim that all pit bull-type dogs are aggressive and that their behavior is genetically determined in a way that justifies a breed ban, is not supported by the cited evidence.

Duffy et al. (2008) found statistically significant average breed differences in several forms of aggression, but they explicitly warn that their finding should be interpreted with caution because within breed variations makes it inappropriate to predict an individual dog’s behavior based solely on breed. They also note that injury risk is higher with larger, more powerful dogs and because stereotypes can bias reporting and perception (Duffy et al., 2008).

In their C-BARQ survey, pit bull type dogs had an only slightly above average stranger directed aggression of 6.8%. This is inconsistent with the claim that all pit bull-type dogs are more dangerous than other breeds (Duffy et al., 2008). There may be elevated concern with dog directed aggression where owners reported 22% of pit bull-type dogs in the study bite/attempted to bite. This is only overshadowed by Akitas’ 29% (Duffy et al., 2008). The paper does not support the claim that pit bull-type dogs are categorically more aggressive toward humans than other dogs.

Heritable is a population statistic. It does not mean that every dog in that breed has that trait. Heritability is defined as the variation due to genetics, divided by variation due to the environment. Aggression-like traits tend to have low heritability and the research papers cited are not about pit bull-type dogs. They caution that the dataset is small and that absolute values should not be treated as the true heritability (Liinamo et al., 2007; Pérez-Guisado et al., 2006). Pérez-Guisado et al., 2006 reported that heritability estimates in English Coker Spaniel puppies (sire h² = 0.20; dam h² = 0.46) and noted that the larger dam estimates implies an important maternal effect (genetic and environment) (Pérez-Guisado et al., 2006).

If the public’s safety and wellness is the primary goal, I urge the community to adopt a behavior-based policy which includes enforced leash laws, address negligent owners, require risk-based management for dogs with documented incidents, and escalating penalties for repeated violations. These are sound approaches to improving public safety without penalizing good dogs and their owners.

Duffy, D. L., Hsu, Y., & Serpell, J. A. (2008). Breed differences in canine aggression. Applied Animal Behaviour Science, 114(3–4), 441–460. https://doi.org/10.1016/j.applanim.2008.04.006

Liinamo, A.-E., Van Den Berg, L., Leegwater, P. A. J., Schilder, M. B. H., Van Arendonk, J. A. M., & Van Oost, B. A. (2007). Genetic variation in aggression-related traits in Golden Retriever dogs. Applied Animal Behaviour Science, 104(1–2), 95–106. https://doi.org/10.1016/j.applanim.2006.04.025

Pérez-Guisado, J., Lopez-Rodríguez, R., & Muñoz-Serrano, A. (2006). Heritability of dominant–aggressive behaviour in English Cocker Spaniels. Applied Animal Behaviour Science, 100(3–4), 219–227. https://doi.org/10.1016/j.applanim.2005.11.005