Adaptive Value

All work and no play makes Jack a dull boy

Playtime, or some time of social interaction, is critical for the development of dogs as a form of interaction with littermates. When a pup is undersocialized during the socialization period, it becomes increasingly fearful of novel situations and humans as it reaches 12 week of age [2].

What about play itself rather than general interaction? There are several theories attempting to explain the function of play.

Surplus Resource Model: this is the "non-functional" hypothesis, developed by Burghardt. According to this proposition, play behavior is an evolutionary side-effect of the mammalian ability to obtain more than sufficient resources. This means that mammals, especially the young, are not limited in their actions by their energy. Thus, play behavior comes about because it can; it does not serve any particular purpose. [7]

Surplus Energy Model: this model also stems from the high success of mammals, and was developed by Schiller and then Spencer. Young are nurtured with more nutrition, resulting in a surfeit of energy that they expend by playing. This activates the central nervous system, thus increasing metabolic rate. The direct benefit of an increased metabolic rate is protection from the cold and avoidance of obesity. [7]

Sensitive Period Hypothesis: the most popular theory, developed by Groos in 1898 and modified by Byers and Walker in 1995. It focuses on the physiological implications of play action, and suggests that the physical component of play serves to differentiate muscle fiber (build and refine muscle groups) and improve and develop cerebellar synapses. This results in an enhanced skill level and a higher level of coordination for the animal. [7]

Self-Assessment: this theory focuses on the mental benefits of play just as much as the Sensitive Period Hypothesis focuses on the physiological. Thompson described this benefit of play. He reasoned that as an animal performs the mentally and physically difficult tasks associated with play, they come to assess their skills at the activities, and consequently the "real-life" activities (actual fighting, actual fleeing, actual copulation) the play imitates. [7]

Spinka, Newberry, and Bekoff proposed a sort of synthesis and expansion of the "Sensitive Period" and "Self-Assessment" theories in their article Mammalian Play: Training for the Unexpected. As suggested by the title of the article, this concept describes play behavior as a rehearsal session that prepares the animal for physically and emotionally stressful events that occur in adulthood (e.g. fleeing, fighting, or an unexpected audial or visual event). By playing, the animal purposefully places itself in a situation where it loses control over its motion and then attempts to regain it rapidly. This lets the animal practice its physical and mental response to the "unexpected."[7]