Extensive research on dog behavior found that puppies who were isolated from human contact between five and twelve weeks were never able to react normally to people later in life. Now called a “sensitive period” because it doesn’t appear to be quite as cut-and-dried as first thought, these early weeks have a profound effect on the behavior of an adult dog. During this time puppies—and their wolf cousins—are primed to take in information about who their social companions are.
