The special issue on the evolution and psychological significance of play in Learning and Behavior covers multiple topics, species, and ages and is most welcome. I hope the issue and thoughtful papers receive the attention that they deserve. With the great influx of research interest in play over the last 20 years, some of the isolation is breaking down between those focused on play in animals, the neuroscience of play, child development, sports, artistic endeavors, folklore, and applications to education, animal welfare, psychological therapy, and so on.
In this issue are 11 papers that, while not addressing all the critical issues in play, do tackle important topics and move the field forward. These papers include research program overviews, conceptual issues, and empirical studies including ones on dogs, cetaceans, children, and indigenous populations.
A true feast.
Rather than primarily react to a specific paper or topic, or individually comment on them all (virtually impossible in a short essay), I will briefly reflect on issues and approaches on display in the papers in the issue. I will not cover each paper directly, but use them as grist for comments that go beyond the points made by the editors, Voogt and Miller in their editorial and opening post. The editors hope for cross fertilization among researchers on diverse topics and species, while also acknowledging a point made by several of us years ago: play is a heterogeneous phenomenon reflecting different causal mechanisms, developmental processes, and evolutionary histories.
In my 2005 book, I tried to address the heterogenous nature of play and its functions by viewing play phenomena as primary, secondary, or tertiary. Play may thus have no adaptive function (either immediate or delayed), aid in maintaining behavioral competencies, or have benefits of many sorts. Play may also be costly, cruel, and even maladaptive (e.g., gambling, risky play such as running class 6 whitewater rapids). Thus, perhaps in contrast to Marek Špinka’s preceding post in this digital event, I argue that the search for the function of play is doomed to failure. The search should be, if that is the researcher’s aim, for the role that play plays in specific aspects, or behavior systems, of the human or nonhuman animal being studied.
It is also important to study whether any of these putative benefits generalize to other behavioral contexts and not just assume generalization. The article on chess in this issue (by Sala and Gobet) is a fine example of this type of approach. The many studies on play ‘fighting’ in rodents also reflect this interest.
Defining and characterizing play was the focus of several papers in this issue (Miller, ). When I started to seriously study play from a comparative perspective, it was clear to me that existing definitions had serious deficiencies. Play was largely thought a feature of mammals and perhaps some birds. My goal was to see if we could identify behavior as play in species and contexts where it had not been seriously considered, as in reptiles, fish, and insects, by removing the anthropomorphic aspects.
This is difficult for many observers who think that play must show obvious signs to them of joy, pleasure, or having fun. I am writing this while attending a small conference of leading animal behavior researchers covering a wide gamut of species and topics. Yesterday I gave a talk on play and ritual where I showed this video clip of a cat and turtle playing tag around a pole:
Immediately someone raised the objection that it was certainly play for the cat but not the turtle, because one could see the cat was enjoying his/her self but we could not know this for the turtle. This comment shows the resistance to expanding the evolutionary and comparative reach of play.
I think the five criteria I derived from the literature that jointly need to be satisfied have done this successfully within the play research community if not outside it. Although the criteria have been slightly refined since 2005, given that play is such a mixed class of phenomena it is to be expected that overarching criteria cannot be overly precise. We need now to have more detailed characterizations of specific types of play such as object play, social play, pretense, and other types sensitive to the contexts and species involved. Several papers in the issue are doing this regarding shared intentionality (Heesen), strategic games (Voogt), imaginary play (Göncü, Gleason), and pretense (Ma).
Tinbergen’s classic 1963 paper on the four aims of ethology, namely to understand the causal mechanisms, ontogeny, evolution, and adaptive function of behavior, was a most useful advance in clarifying the strategies and tactics of behavior research (see the article in the special issue by Palagi). Yet in my mind it was incomplete in that it ignored the psychological and private experiences of the organism. Although influenced by von Uexküll’s perceptual and effector components of behavior, Tinbergen ignored von Uexküll’s focus on the ‘inner world’ of the animal. Indeed, the irony here is that Tinbergen in that 1963 paper rejected the study of play as it was too subjective! Given that a focus of this issue of Learning & Behavior is on the psychological significance of play, the message I tried to deliver in 2005 on the importance of adding a fifth aim, that of private experience, to Tinbergen’s four seems especially salient.
Often those studying play in humans focus on pretend, imaginative, sociodramatic, and educational play, whereas those studying animal play focus more on overt behavior in the three basic categories of locomotor/rotational play, object/predatory play, and social play (typically wrestling, chasing, etc.). This is shown in this issue in papers discussing play in rodents (Pellis), dogs (Merhkam), cetaceans (Hill), and nonhuman primates (Palagi). The progress being made in understanding rodent, especially rat, social play is far ahead of the pack, but studies on breed differences in dogs and relationships across play types addressed in this issue reflect the growing importance of canine studies in the field of comparative cognition in general.
While the literature cited in the human and nonhuman focused papers in this issue overlap to some extent, the disconnect between them is still too great. Human-play researchers often focus on what I generically call mental play, while nonhuman play researchers focus largely on active behavioral play. While ‘mental’ play is a special challenge for those studying nonhuman animals, active physical behavioral play is not so difficult to study with humans. Certainly, there is research on behavioral play in humans, but too often it seems focused on what it tells us about mental capacities rather than its role and function qua behavior, and especially its role on functioning in social groups.
The paper on shared attention (Heesen) is an admirable bridge across these literatures. The paper on a Piagetian analysis of behavioral development in whales and dolphins (Hill) also is one of the most thorough and insightful such efforts and shows what students of nonhuman animals can gain from the child development literature. The paper on mimicry (Palagi) also effectively shows the value and importance of comparative papers that include the human animal to derive important insights that bridge the anthropocentric divide. Indeed, play in all its guises may be one of the best conduits in developing a genuine integrative comparative psychology that includes the human animal.
One important means of aiding this integration is relating specific research papers to some of the more important integrative theoretical books on play. I also think that some scholars are unduly neglected. Only one article cited Tom Henricks, but not his recent book (Henricks, 2015). One article cited Robert Mitchell’s work on pretend play in human and animals, but his work on defining play as being focused on intentionality was not cited. Two papers cited Brian Sutton-Smith, perhaps the most important play scholar since Huizinga (who was cited by one article). Henricks and Sutton-Smith (1997) provide perspectives that reach into the sociological, historical, anthropological, and other areas that will eventually need to be incorporated into a true integrative conception of play. Such integration will best be done by accumulating careful, detailed studies of specific and diverse play phenomena, and this special issue is a major advance in reaching this ‘impossible dream.’