Copyright © 1999 Massachusetts Institute of Technology
Recently, the scientific study of play behavior has undergone many significant changes. New data are forcing people to give up old ideas and set ways of thinking about this phenomenon. Most researchers recognize the importance of rigorous interdisciplinary collaboration in play research (Pelligrini 1995; Bekoff and Byers 1998; Burghardt 1999), and the interactions among those studying humans and nonhumans are producing exciting new results. Currently, workers in many areas are conducting detailed theoretical, observational, and experimental analyses of play in mammals (including humans) and birds. (Using criteria that are employed to characterize play in mammals and birds, it appears that some reptiles might also play [Burghardt 1999].) They are concerned with such topics as evolution, ecology, development, social communication, individual well-being, neurobiology, LEARNING, and cognition (for references see Bekoff and Byers 1981, 1998; Fagen 1981; Smith 1982 and commentaries, 1984; Martin and Caro 1985; Burghardt 1999; Bekoff and Allen 1992, 1998; Allen and Bekoff 1994, 1997; Brown 1998; Pelligrini 1995; Sutton-Smith 1998).
Because social play (hereafter play) is a widespread phenomenon, especially among mammals, it offers the opportunity for comparative work on animal cognition, including such areas as intentionality, communication, and information sharing (Bateson 1956; Bekoff 1998; Bekoff and Allen 1992; Allen and Bekoff 1994, 1997). Through difficult to define and to study, play is generally recognized as a distinctive category of behavior. Difficulties with functional definitions led Bekoff and Byers (1981: 300-301; see also Martin and Caro 1985) to offer the following definition: "Play is all motor activity performed postnatally that appears [my emphasis] to be purposeless, in which motor patterns from other contexts may often be used in modified forms and altered temporal sequencing. If the activity is directed toward another living being it is called social play." This definition centers on the structure of play sequences -- what individuals do when they play -- and not on possible functions of play.
Why engage in social play? Despite physical risks (and perhaps other costs) associated with play, many individuals persistently seek it out. A major question centers on why play has evolved and what benefits outweigh the energy and risk costs of play. Play may serve a number of functions simultaneously (for example, socialization, exercise, practice, or cognitive development) and there are species, age, and sex differences. Functional (evolutionary) accounts are often tied to analyses of what individuals do when they play. Although many agree that play seems to have something to do with motor development, or with the development of cognitive skills that support motor performance, hard evidence is scant and opinions are divided. One important theme stemming from recent comparative research is that functional accounts of play resist being pigeonholed into simple and misleading summary statements. In the past, for example, play-fighting was considered important in learning fighting skills that would be used in adulthood or for physical training. Although in some species play may be important for the development of certain skills, in others this might not be the case. For example, play-fighting does not seem to be important in the development of motor training for fighting skills in some rats (Pellis and Pellis 1998), but others (Biben 1998; Heinrich and Smolker 1998; Miller and Byers 1998; Thompson 1998; Watson 1998) have shown that play may be important in the development of motor training, cognitive/motor training, or in the development of other social skills (social competence) in birds and mammals, including humans.
Questions dealing with the immediate causes and benefits of play also need more attention. Research on the neurobiology of play also centers on possible causes (Byers 1998). For example, it appears that dopamine, serotonin, and norepinephrine are important in the regulation of play, and that a lot of the brain is active during play (Siviy 1998). Based on these data, some have suggested that play may facilitate coping with environmental stressors and be important in coordinating an organism's response to stress. These data also provide the basis for more informed discussions of the role of play in learning and promoting creativity. Neurobiological data are also essential for assessing hypotheses about whether play is a pleasurable activity for nonhumans as it seems to be for humans, and there is some neurochemical evidence that suggests that it is. In light of these neurobiological data, scientists who study play might be less resistant to explanations that appeal to enjoyment as a motivator for the activity.
Communicative and cognitive aspects of play also are receiving attention. When individuals play they typically use action patterns that are also used in other contexts, such as predatory behavior, antipredatory behavior, and mating. These action patterns may not be intrinsically different across different contexts, or they may be hard to discriminate even for the participants. To solve the problems that might be caused by confusing play with mating or fighting, many species have evolved signals that function to establish and to maintain a play "mood." In most species in which play has been described, individuals have to communicate that "this is play, not fighting, mating, or preying," and there are data that show that certain signals are used to communicate "what follows is play" or "let's keep playing no matter what I just did or plan to do." For example, in infant coyotes, wolves, and domestic dogs, a behavior pattern called the "play bow" is not performed randomly, but rather immediately precedes or immediately follows behavior patterns that can be misinterpreted (for example, biting accompanied by vigorous side-to-side shaking of the head; Bekoff 1995). Suffice it to say, in most species in which play has been described, play-soliciting signals (or play markers) appear to foster some sort of cooperation between players so that each responds to the other in a way consistent with play and different from the responses the same actions would elicit in other contexts. There is little evidence that play signals are used to deceive others.
Bekoff and Allen (1998) point out that the strongly cooperative nature of much social play makes it a useful model for study of the communication of intention. For example, when two individuals engage in play-fighting, there is a risk of injury to each, especially if one switches from play- fighting to real fighting. Somehow, the playful and cooperative nature of the interaction is maintained, even though the motor acts themselves may closely resemble aggression. How do individuals "read" play intention in a conspecific? Cooperative social play may involve rapid exchange of information on intentions, desires, and beliefs. Discussions of self-handicapping (individuals do not bite or hit others as hard as they can) and role-reversals (dominant individuals allow subordinate individuals to dominate them) in play by individuals of many taxa can also inform cognitive inquiries. We can also ask what are the consequences of failure to play for individuals of species in which cooperative social play is a form a social cognitive training. By reviewing the lives of homicidal and antisocial personalities and the influence of diseases on early human behavior, Brown (1998) presents a set of interesting correlations showing that play in childhood is required for the social integration of humans. Data on nonhumans also support this idea.
The flexibility and versatility of play make it a good candidate for comparative and evolutionary cognitive studies. These data may provide important insights into what might be going on in an individual's mind.
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Copyright © 1999 Massachusetts Institute of Technology