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Play. Jeff Schank ANB 218a 2013. What is Play?. Criteria for play Incompletely functional; spontaneous, pleasurable, rewarding, or voluntary;
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Play Jeff Schank ANB 218a 2013
What is Play? • Criteria for play • Incompletely functional; • spontaneous, pleasurable, rewarding, or voluntary; • differs from other more serious behaviors in form (e.g., exaggerated) or timing (e.g., occurring early in life before the more serious version is needed); • is repeated, but not in abnormal and unvarying stereotypic form (e.g., rocking or pacing); and • is initiated in the absence of severe stress.
Types of Play • Solitary locomotor-rotational play • Vigorous motor acts, typically performed alone (e.g., playful running and twisting in ungulates, and somersaulting in monkeys) • Object play • Involves the playful use or manipulation of inanimate objects (e.g., a dog retrieving a stick or a cat batting a ball) • Social Play • Social play involves two or more players that are usually, but not always conspecifics. • Typical movement patterns involve chasing, wrestling, and tail-pulling, and even a form of peek-a-boo • Of all social play patterns, rough-and-tumble play (R&T), or play-fighting, is most frequently studied in animals
Theories of Play: Historical View • Surplus Energy • Animals play when the have surplus energy and they are in good health—Why play? • Instinct-Practice • Instinctive behavior requires practice to become optimal (assumption) and play is a form of practice—Why and how is play practice? • Recapitulation • Play is a vestigial relic from past evolution—Why is play so common?
Theories of Play: Modern Functional View • One problem with the older theories is that each was viewed as an independent theory • However, aspects of each are relevant to the modern functional view • Functional view • Play likely has multiple functions: motor training, practice, and socialization • Very difficult to test the functions of play because presumably the fitness benefits are delayed till adulthood
Functional Theories • Motor training • Physical exercise: No evidence • Cerebellar synaptogenesis: play occurs after most of cerebellar synaptogenesis is complete • Training for unexpected events • Play allows an animal to acquire kinematic and emotional skills required for dealing with unexpected events • Predicts play should be more frequent in changing environments • Can’t explain why play is less frequent is poor (food shortages, stressful, challenging) environments
Functional Theories • Practice • Little evidence that play facilitates learning corresponding adult behaviors • Social benefits • Enhancing social skills • Strengthening social bonds • Reducing aggression • Refining social assessment • Learning and promoting cooperative behavior • sharing • Reciprocity • Altruism • Fairness • Little evidence to support any of these theories since some animals deprived of social play still develop adult social competencies • Playing animals seem to learn fairness and cooperation, and may even punish cheaters by not playing with them • I’ll come back to social play later
Costs and Benefits of Play • Costs • Injury from falls or aggressive retaliation • Reduced time spent in survival behaviors (e.g., foraging) • Expenditure of energy • Increased predation risk as a result of reduced vigilance and the conspicuousness of play to predators • Delayed Benefits • Nunes (2004) found that social play in female Belding’s ground squirrels increased reproductive success during their first breeding season
Interspecies Play • Examples of interspecies play • Lion and Tiger • Wolf, Bear, Human • Cat and Owl • Rat and Cat • Kangaroo and Lemur • Dog and Deer • Polar Bears and Dogs • Cat and Dolfins • Monkeys and Dogs • Humans playing with Stingray? • How do we explain interspecies play? • Does it tell us anything about social play? • Does it tell us anything about the evolution of social play?
Why is Social Play Beneficial? • It seems plausible if not obvious that social play could derive its fitness benefits by learning the skills necessary for adult cooperation • The evolution of cooperation, however, is hard to explain, especially at low frequencies • Suppose a social play gene is introduced into a population of non-cooperators at low frequencies • How do juveniles with the play gene find others to engage in social play? • If they do, and learn to cooperate, adults would be at a disadvantage in a population of mostly non-cooperators • It would appear that the evolution of social play by facilitating adult cooperation is improbable at best
A Model of the Evolution of Social Play • Sometimes intuitions can be misleading! • Let’s consider agents with generic biological properties characteristic of animals that engage in social play and adult cooperation • Agents can • Movement and Aggregation • Development (juvenile adult) • Learning • Reproduction • Parental investment • Life span • Foraging for resources
Cooperation Prisoner’s Dilemma: T> R > D > S (e.g., T = 5 > R = 3 > D = 1 > S = 0) Stag Hunt: R> T ≥ D > S (e.g., R = 2 > T = 1 ≥ D = 1 > S = 0)
Learning to Cooperate Rescorla-Wagner learning model
Conclusions • Social play could evolve facilitating the learning of adult cooperative skills • How does it work? • Sewall Wright’s shifting balance theory • Effectively neutral mutations in low frequency • Parental investment: inheriting wealth • There is much to be done to understand play • None of Tinbergen’s 4 questions have been adequately developed
