Animal Play brings together the major findings about play in a wide range of species including humans. Topics include the evolutionary history of play, play structure, function and development of play, and sex and individual differences.

List of contributors.
Introduction. Marc Bekoff and John A. Byers.

1. The evolutionary origins of play revisited: Lessons from turtles. Gordon M. Burghardt.
2. Play in common ravens (Corvus corax). Bernard Heinrich and Rachel Smolker.
3. Object play by adult animals. Sarah L. Hall.
4. Kangaroos at play: Play behaviour in the Macropodoidea. Duncan M. Watson.
5. Intentional communication and social play: How and why animals negotiate and agree to play. Marc Bekoff and Colin Allen.
6. Structure-function interface in the analysis of play fighting. Sergio M. Pellis and Vivien C. Pellis.
7. Sparring as play in young pronghorn males. Michelle N. Miller and John A. Byers.
8. Squirrel monkey play fighting: Making the case for a cognitive training function for play. Maxeen Biben.
9. Self assessment in juvenile play. Katerina V. Thompson.
10. Biological effects of locomotor play: Getting into shape, or something more specific?. John A. Byers.
11. Neurobiological substrates of play behavior: Glimpses into the structure and function of mammalian playfulness. Stephen M. Siviy.
12. Play as an organizing principle: Clinical evidence and personal observations. Stuart Brown.

Burghardt, Gordon M. The evolutionary origins of play revisited: Lessons from turtles. Bekoff & Byers (1998), p. 1-26.

Abstract: Reviews recent data suggesting that object, locomotory, and social play do occur in some turtles. The author describes phenomena that, if seen in a mammal or bird, would readily be labeled playful by most observers. These examples are compared in detail with frequently noted criteria for play. The author believes that these examples may aid in identifying the primary processes by which "play" originated and evolved in ancient vertebrates and their modern descendants. Understanding the origins of play may provide the framework from which the highly diverse and complex structures of mammalian and avian play could evolve through a series of secondary or derived processes. The author believes that play may be an important aspect of behavioral innovation in the evolution of vertebrates and outlines some of the lessons turtle might teach readers.

Heinrich, Bernd and Rachel Smolker. Play in common ravens (Corvus corax). Bekoff & Byers (1998), p. 27-44.

Abstract: Discusses the definition and purposes of play behavior in ravens. The authors include observations of ravens held in an outdoor enclosure to provide the reader with a sense of the nature of raven play. The chapter also covers object exploration and manipulation, play catching, flight play, bathing, sliding and hanging, as well as allospecific interactions and vocal play. The authors discuss the relationship of these behaviors to aspects of raven biology and ecology.

Hall, Sarah L. Object play by adult animals. Bekoff & Byers (1998), p. 45-60.

Abstract: Discusses the definitions of object play, and includes a brief description of object play by juveniles to serve as a comparison. The focus of this chapter is object play by adult animals, a type of behavior that is less commonly observed than juvenile play and perhaps even more resistant to explanation. The author covers the structure and function of adult play behavior, as well as object play behavior in adult predatory animals. Experimental evidence for the association of predation and object play in adults is cited and directions for future study of object play by adult are suggested.

Watson, Duncan M. Kangaroos at play: Play behaviour in the Macropodoidea. Bekoff & Byers (1998), p. 61-95.

Abstract: Summarises and compiles the existing data on play in the Macropodoidea (kangaroos). The first part of the review discusses the quality of the available data. Data quality affects the limits to which it can be confidently used to answer functional and evolutionary questions. The generally poor quality of the data for macropodoids explains why functional and evolutionary generalisations regarding play are currently premature and sets a basis for understanding why there may be confusion as to what is and what is not play in macropodoids. Following this is a review of play in macropodoids: what types of play occur and their main structural elements. The relationship between play and real fighting is examined in the third part of the review. The observations that some of the ritualised fights described in the literature often include characteristic features of play seen in placentals are addressed. Rather than reflecting a taxonomic difference in the fighting behavior between macropodoids and placentals, it is argued that some of these fights were misclassified play fights. Finally, the function and evolution of play in macropodoids are discussed.

Bekoff, Marc and Colin Allen. Intentional communication and social play: How and why animals negotiate and agree to play. Bekoff & Byers (1998), p. 97-114.

Abstract: Examines intentional communication and social playing in animals. The chapter covers the evolution, definition of play, including discussion of the possibility of an evolutionary biology of play and the intentionality of play. The authors discuss play signals, and also look at the broader cognitive context of play. The chapter concludes with remarks on social play and comparative studies of animal cognition. Full text (Cogprints -- external).

Pellis, Sergio M. and Vivien C. Pellis. Structure-function interface in the analysis of play fighting. Bekoff & Byers (1998), p. 115-140.

Abstract: Discusses the case for play fighting in animals as having the function of rehearsing adult combat. The authors state that the idea would be more compelling if the structure of play fighting had design features suitable for this purpose. The chapter shows that the very behavioral features that make play fighting play, also make play fighting a poor means of rehearsing combat skills. While some evidence suggests that such rehearsal may occur for some combat tactics in some situations, the practice hypothesis cannot account for the form of play fighting in most species.

Miller, Michelle N. and John Alexander Byers. Sparring as play in young pronghorn males. Bekoff & Byers (1998), p. 141-160.

Abstract: Attempts to determine what the purpose and wager is between sparring ungulate males. To answer this question the authors describe the context in which sparring is observed as well as the common participants in both pronghorn and other species in which sparring has been studied. In this and other recent studies, there has been an attempt to quantify, rather than simply describe, sparring in a manner that will help to resolve its functions. The authors define sparring and describe the form it takes in various organisms. They then present a detailed analysis of sparring in young pronghorn males.

Biben, Maxeen. Squirrel monkey play fighting: Making the case for a cognitive training function for play. Bekoff & Byers (1998), p. 161-182.

Abstract: Examines the case for a cognitive training function of play fighting in squirrel monkeys. The author examines the role of dominance in play, and how dominance relationships determine play decisions. Also considered is the importance of winning vs. the play experience itself. Finally, the author covers the benefits and costs of play fighting, including possible risks and concludes the chapter with a consideration of play as training for serious fighting.

Thompson, Katerina V. Self assessment in juvenile play. Bekoff & Byers (1998), p. 183-204.

Abstract: Considers several aspect of animal play that seem inadequately explained by current theory. These include (1) the possible implications of the brief, repetitive nature of play behaviors, (2) whether or not play is a unitary category, (3) the ambiguous relationship between play and aggression, and (4) the question of whether play is competitive. The author then suggests an alternative interpretation of play, that play is a mechanism by which a developing individual can assess its capabilities.

Byers, John Alexander. Biological effects of locomotor play: Getting into shape, or something more specific? Bekoff & Byers (1998), p. 205-220.

Abstract: Discusses why the getting-into-shape hypothesis of animal locomotor play is unlikely, for three reasons. First, all getting-into-shape physiological responses are very transitory, and disappear shortly after exercise stops. Second, the kind and amount of exercise performed in play in most species is probably insufficient to prompt physiological training responses. Third, exercise responses are not age-limited; animals can exercise and obtain a training response at any age. Finally, the author suggests a method by which one can evaluate any other functional hypothesis (e.g., play provides motor learning) about play.

Siviy, Stephen M. Neurobiological substrates of play behavior: Glimpses into the structure and function of mammalian playfulness. Bekoff & Byers (1998), p. 221-242.

Abstract: Examines the role of the brain and its systems in play behavior in animals. The author suggests that in addition to lending insight into the evolutionary origins of play, studies that focus on the neural basis of play behavior can also be useful in generating testable hypotheses about possible functions of play. The chapter covers methodological considerations, a lengthy discussion of the neurochemistry of play, and tentative hypotheses regarding the function of play.

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