In 1963, a young macaque monkey was observed venturing into a hot spring to retrieve food which had fallen in. Soon, other macaques began to enter the spring, and over a few years this behavior was adopted by the entire troop. Prior to 1963, no macaques had ever been observed in the hot spring; by 1990, the troop was regularly spending time there during the winters. Thus, these macaques are able to adopt and pass on new patterns of social behavior, and are not complete captives of their genetic heritage. Which one of the following is an assumption required by the argument above? ['The social behaviors of macaques are completely independent of their genetic heritage.', 'New patterns of behavior that emerge in macaque populations over the course of a few years or decades are not necessarily genetically predetermined.', 'Mutations in the genetic heritage of a certain variety of macaques can occur over a time span as short as a few years or decades.', "The macaques' new pattern of behavior will persist over several generations."]