Puppies that received no exposure to people during the sensitive period of socialization (3 – 12 weeks) were always fearful and never able to have normal social interactions with humans (Freedman et al., 1961).

Freedman, D.G., Elliott, E., and King, J.A. (1961). Critical period in social development of dogs. Science, 133, 1016-1017.

Emotionally arousing stimuli, either positive or negative, can accelerate the sensitive period of socialization and these can impact a dog for a lifetime. Veterinary procedures that induce trauma in some dogs, such as vaccinations or even grooming, can also be critical during this time window (Scott & Fuller, 1965).

Scott, J.P. and Fuller, J.L., (1965). Genetics and the social behavior of the dog. 1st ed. Chicago, IL: University of Chicago Press.

Fear learning, also known as Hazard-Avoidance Behavior, varies by breed and individual dog. The average puppy’s fear period “turns on” at 49 days (Zimen, 1987).

The onset of fear learning, or “Hazard-Avoidance Behavior”, varies among breeds and individuals, with the average puppy’s fear periods emerging at 49 days (Morrow et al., 2015).

Morrow, M., Ottobre, J., Ottobre, A., Neville, P., St-Pierre, N., Dreschel, N. and Pate, J.L. (2015). Breed-dependent differences in the onset of fear-related avoidance behavior in puppies. Journal of Veterinary Behavior: Clinical Applications and Research, 10, 286- 294.

To avoid “localization” or site attachment”, where pups are only comfortable in limited, specific environments, socialization and early exposures must be done in many different locations before 6-7 weeks of age (Scott & Fuller, 1965).

Scott, J.P. and Fuller, J.L., (1965). Genetics and the social behavior of the dog. 1st ed. Chicago, IL: University of Chicago Press.