When puppies are socialized with humans, particularly between the ages of eight and twelve weeks, they develop social skills around people. Those that do not receive adequate socialization during this period may display fearful behavior around humans or other dogs as adults. The optimum period for socialisation is between eight and twelve weeks; professional animal trainers and the American Kennel Club advise puppies should be introduced to "100 People by 12 Weeks" and have encountered a wide and varied selection of people and environments.[7]