Animal Play: Evolutionary, Comparative and Ecological Perspectives. Marc Bekoff and John A. Byers, eds. 274 pp. Cambridge University Press, 1998. $32.95.
Next time you visit the zoo, study the young animals. You will notice, perhaps to your surprise, that young animals not only play, they play a lot. And play is not a luxury afforded only by those animals lucky enough to lead the cushy life of a zoo creature—animals in nature play all the time.
When behavioral ecologists hear that animals spend a great deal of time engaged in a particular behavior, a little light goes off in their heads and they immediately start thinking "adaptation." After all, every behavior has costs and benefits, and only those in which the latter outweigh the former should stick around very long; hence most behaviors, especially those that animals do often, are good candidates for being adaptations. In fact, behavioral ecologists can go overboard on this front and at times are accused of creating "adaptationist stories." Yet somehow people have tended not to weave adaptationist stories about the evolution of play—rather, just the opposite. Every possibility besides play as an adaptation was given a day in the sun. Once you read Animal Play: Evolutionary, Comparative and Ecological Perspectives, you will see that there is little doubt now that play has been shaped by natural selection—that is, it is adaptation.
This ambitious volume's editors lay out five critical issues regarding play: Which animals play? What are the typical age-specific rates of play? What exactly does play do for a young animal? What mechanisms produce and maintain play? And what are the communicative and cognitive aspects of play? To address these issues, contributors from a variety of disciplines (psychology, ecology, ethology and neurobiology) examine play in many different taxa (birds, mammals, reptiles) from both ultimate and proximate perspectives.
As with any compilation, there is considerable variation in quality, but the book is well edited. I shall focus on the material I found most illuminating.
Guess which animal is the subject of the opening (and thus critical) chapter in this book on play. The chimp? Dog? Cat? No. The turtle. That's right. Gordon M. Burghardt's logic for studying play in turtles goes as follows: If you want to truly understand play in mammals (including humans), you must begin by understanding the evolution of play. To do that, you must study play in creatures that are ancestral to mammals and work your way up. Hence, turtles. Burghardt's turtle studies shed light on the evolution of play as well as the current utility of play—issues of great interest to those trying to better understand play in mammals. This work is a testament to the power of a comparative approach to understanding a behavior's function.
Bernd Heinrich and Rachel Smolker's chapter on play in ravens is both extremely well written and informative. They demonstrate that juvenile ravens are very interested in playing with anything new. When they mature, adults are not scared of what they played with as youngsters but are afraid of almost everything else. Heinrich and Smolker show nicely that play in ravens may help in learning, manipulating the environment and signaling social status.
Aside from their discussion of kinesthetics (which I found a bit distracting), Marc Bekoff and Colin Allen offer a wonderful introduction to how "cognitive ethologists" attack questions regarding play. They clearly introduce the complicated topic of intentionality, and the concepts they lay out are nicely illustrated with examples from canids (as well as other groups).
From Sergio M. Pellis and Vivien C. Pellis the reader learns that play fighting is often assumed to be rehearsal for adult combat. If this is so, Pellis and Pellis argue, behavioral features associated with play fighting should have design features that enhance adult fighting ability, yet the authors find little support for this "practice" hypothesis. For example, the most difficult aspects of fighting should be practiced most, yet the evidence does not suggest that this is the case. In addition, play fighters do not practice offense and defense simultaneously—a critical skill one must have in "true" fighting.
Maxeen Biben's chapter on squirrel monkey play fights is particularly illuminating. Male squirrel monkeys choose play partners they can dominate (dominance for males is mostly a function of rank outside play activities) and play allows for occasional reversals of dominance, providing subordinates and dominants experience in what it is like to be in the converse role. This is particularly important in squirrel monkeys, as all males must work their way up an established dominance hierarchy in a group, and at some time or another all males are low-ranking. Role reversal in play allows one to know how to do that. In addition, Biben suggests that squirrel monkey play fights provide experience at gauging the intention of others.
Co-editor John A. Byers follows, putting to bed the notion that play serves the function of "getting into shape." He shows three reasons why the getting-in-shape hypothesis is weak—namely, that physiological processes are often short-lived, that the kind and amount of exercise displayed is insufficient to prompt physiological training responses, and, if getting in shape were key, this would hold for an organism's entire life, whereas play is primarily an act of the young. Byers ends by introducing his own "sensitive period" hypothesis for the evolution of play.
Rounding things off for this volume, Katerina Thompson demonstrates nicely that one important function of play behavior is assessment—of one's relative competitive ability and of the best strategy to optimize the amount of time spent playing.
Aside from a chapter that conflates ultimate and proximate views of play and one that I found almost completely uninformative, my only broad-scale reservation about this book is that it is completely devoid of any mathematical models of how play behavior evolved. Game theory and other optimality techniques seem well suited for this task, and I am surprised they were not included at some level. Overall, however, readers interested in play behavior (and behavior in general) will find this book a worthwhile read.—Lee Alan Dugatkin, Biology, University of Louisville