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Play “We have seen that there are many, indeed innumerable, ways of characterizing and defining play. All single-criterion definitions such as ‘play is behavior done for its own sake,’ ‘play is not serious,’ ‘play is pleasurable behavior,’ or ‘play is preparation for the future’ fail because they include much that clearly is not playful in any traditional sense even if the criteria could be objectively applied. Thus we still face the dilemma of deciding in any given example or species whether we are dealing with a presumptive example of play. This is not just a pedantic question. In order to try to elucidate the genesis of play, we must use the comparative method. In order to apply the comparative method, we need to be able to know what we are comparing across species and populations. If we are studying the ontogeny of play and its fate and transformations in individuals, we also need to know whether we are comparing related activities or those that just look similar. After considering all the proposed criteria and how they might be applied to the occurrence of play in animals never considered playful (e.g., turtles), I have now decided that five key criteria are possible. It seems to me that applied in a careful manner, they can distinguish play from virtually all other phenomena with which it might be confused, including exploration and curiosity on one hand and stereotyped behavior on the other. The key here is that all five criteria have to be simultaneously satisfied for the label of play to be attached. Equally important is an additional proviso: When a criterion contains more than one attribute, only one needs to apply for the criterion to be met. 1. The performance of the behavior is not fully functional in the form or context in which it is expressed; that is, it includes elements, or is directed toward stimuli, that do not contribute to current survival. The critical phrase is ‘not fully functional,’ instead of purposeless, nonadaptive, or having a delayed benefit. Now this clearly does not eliminate all instances of nonplay behavior. We know, for example, that many predatory chases of prey be lions are unsuccessful, as are defensive attacks by prey and rivals. Many courtship attempts, indeed most attempts in many species, are unsuccessful. We also can deceive animals with models, and nature does this with mimics. Thus, many performances of behavior do turn out to be ineffective, misdirected, and unsuccessful. We would not, for these reasons, call them play. 2. The behavior is spontaneous, voluntary, intentional, pleasurable, rewarding, reinforcing, or autotelic (‘done for its own sake’). Only one of these often overlapping concepts needs to apply. Note that this criterion also accommodates any subjective concomitants of play (having fun, enjoyable), but does not make them essential for recognizing play. Note the ‘or’ in the definition. Scientists averse to anything tainted with anthropomorphism might not accept that a behavior is pleasurable for a rat, but may accept that performing it may be reinforcing. Physiologists may not want to use the concept of spontaneous because it may imply that the behavior is uncaused. Similarly, intention (or intentionality) may be key words for those who object to voluntary. 3. It differs from the ‘serious’ performance of ethotypic behavior structurally or temporally in at least one respect: it is incomplete (generally through inhibited or dropped final elements), exaggerated, awkward, or precocious; or it involves behavior patterns with modified form, sequencing, or targeting. Notice that this is a structural and temporal descriptive criterion that acknowledges, but does not require, that play may be found only during a limited period early in an animal’s life. Although individual variation may be more common in play than in other behavioral contexts, 1 Play this needs to be quantitatively assessed. The variances from normal ‘serious’ ethotypic behaviors seen in various guises in play may offer the illusion that the play is free or creative when it is just the shift from the expected, coupled with our own fascination, that is at work. Also, since play may involve many kinds of different objects, many being artificial in captivity, variability is to be expected, just as a wolf stalks a bison differently than it hunts a rabbit. 4. The behavior is performed repeatedly in a similar, but not rigidly stereotyped, form during at least a portion of the animal’s ontogeny. This criterion explicitly counters the apparent freedom, flexibility, and versatility of play that have been so often noted. It is clear from the literature that repetition of patterns of movement is found in all play and games in human and nonhuman animals. It is also useful in distinguishing exploratory responses to novel stimuli, which typically habituate quickly, from the play actions that may follow initial exploratory behavior. Repeated actions also facilitate the use of play in learning or improving skill and . . . an ‘urge’ to repeat behavior (try and try again) may be essential for play to have functional and adaptive roles in behavioral development and psychological well-being. Play, then, is something that is repeatedly performed, often in bouts, during a predictable period in the animal’s life (which in some cases may be virtually life-long). 5. The behavior is initiated when an animal is adequately fed, healthy, and free from stress (e.g., predator threat, harsh microclimate, social instability), or intense competing systems (e.g., feeding, mating, predator avoidance). In other words, the animal is in a ‘released field.’ One value of these five criteria is that they effectively link the different kinds of play: locomotor, object, and social. Play manifests itself in many ways. Whether all play shares some common phyletic history or physiological underpinnings is not the question at issue now. For the sake of convenience, I will refer to the ‘big five’ criteria for identifying play as: 1. Limited immediate function 2. Endogenous component 3. Structural or temporal difference 4. Repeated performance 5. Relaxed field Keeping in mind the nuances underlying each word, a one-sentence definition could then read as follows: Play is repeated, incompletely functional behavior differing from more serious versions structurally, contextually, or ontogenetically, and initiated voluntarily when the animal is in a relaxed or low-stress setting (pp 68-82). The following conclusions, while they are based on different levels of analysis, reflect the five ethological aims discussed in chapters 1 and 5. 1. Play behavior is recognized by five criteria. Playful activities can be characterized as being (1) incompletely functional in the context expressed; (2) voluntary, pleasurable, or self rewarding; (3) different structurally or temporally from related serious behavior systems; (4) expressed repeatedly during at least some part of an animal’s life span; and (5) initiated in relatively benign situations. 2. Play is a heterogeneous category and different types of play have their own phylogenetic and developmental trajectories. 3. The comparative evidence shows that play is not limited to some or even all placental mammals, but is found in a wide range of animals, including marsupials, birds, turtles, lizards, fish, and invertebrates. 2 Play 4. Animals that play often share common traits, including active life styles, moderate to high metabolic rates, generalist ecological needs requiring behavioral flexibility or plasticity, and adequate to abundant food resources. Object play is most often found in species with carnivorous, omnivorous, or scavenging foraging modes. Locomotor play is prominent in species that navigate in three-dimensional (e.g., trees, water)or complex environments and rely on escape to avoid predation. Social play is not easily summarized, but play fighting, chasing, and wrestling are the major types recorded and occur in almost every major group of animals in which play is found. 5. Play may be arranged along a continuum so that much play may have no important evolved adaptive function (primary process play), while other types of play may have secondarily evolved important roles in maintaining or developing and enhancing behavioral performance and cognitive and emotional well-being. Demonstrating such roles, however, has been fraught with difficulties. 6. The genesis of play lies in primary process play with few, if any, immediate adaptive consequences. Such playlike behavior may then be favored by natural selection and eventually become adaptive, even essential, and incorporated into the behavioral repertoire. Play may also represent the precocious maturation of behavior before it is required for survival. Rich and complex play repertoires were facilitated by the evolution of parental care. Much play may be derived from juvenile instinctive behavior that is no longer honed by natural selection operating on its original precocial form and thus is open to neural and behavioral reorganization. 7. Play originally arose from proximate processes such as instinctive behavior and associated neural organization, and the performance of playful acts may be rewarding (autotelic) regardless of their adaptiveness or function. Thus play may be derived from, as well as incorporated into, many different behavior systems. The emotional aspects of play found so compelling are typically found in social animals or those from a highly social ancestry. 8. The evidence for the functional role of play is limited and consequently play has not entered the mainstream of behavioral research in biology, psychology, or the social sciences. 9. The brain mechanisms underlying play are diverse. The neural substrates of play in vertebrates have their origin in structures in the basal ganglia of the forebrain, the cerebellum, and may involve projections to the limbic system (affect) and cortex, especially the premotor and prefrontal areas (context assessment and performance skill). Midbrain structures (e.g., thalamus and hypothalamus) are sources of the sensory and motivational processes that underlie behavioral performance in play. Neurotransmitters (such as dopamine and opioids) and hormones also have influences on play that are still poorly understood, but undoubtedly important. 10. Our understanding of play will only be enhanced when its study is embedded in the normal lives of animals and looked at from a phylogenetic perspective. Experimental and neuroscience studies of play in a few model species can identify some mechanisms and developmental processes, but they will never be able to solve the conundrums of play in isolation from evolutionary processes. 11. Play is a crucial test for the power of science to understand ‘mysteries,’ and its effective study requires integrative and interdisciplinary work by the best scientific minds as well as intensely focused research by specialists (pp. 382-283). The survey of play in diverse animals and the resulting phylogenetic trees show that it is a diverse phenomenon that evolved independently and was even secondarily reduced or lost in 3 Play many groups of animals. A phylogeny of the major animal groups shows that the craniate vertebrate (backboned) animals and invertebrates have long and separate lineages with many branches. Only in animals with several life history, ecological, and physiological attributes did play appear, become prominent, and evolve complex forms. Important adaptive roles for play are thus derived and perhaps evolved in tandem with putative ‘plasticity genes.’ The field of molecular genetics has begun to pay attention to the interaction of specific genes with developmental and life history processes in the expression of many traits of animals. Underlying the grand biological diversity in the world is a surprisingly conservative genetic toolkit. Traits that were thought to have arisen completely independently in animals separated by hundreds of millions of years, such as eyes in flies and mice, are controlled by similar genes; introducing the corresponding mouse gene into a fly induces compound eye tissue, not mouse-type eye tissue. Thus although play arose many times in evolution, it may have been the result of common environmental contexts that activated a suite of retained homeotic hox genes which, although they may have other functions, could be repeatedly coopted in the service of playlike traits. With a conserved and widely shared genome available, play, as surplus resource theory posits, could then readily appear whenever physiological (including neural), life history, energetic, ecological, and psychological conditions, in conjunction with a species’ behavior repertoire, reached a threshold level to activate genetic processes. An important task for the future is to tease apart these conditions, including the genes, and rigorously evaluate their contribution to both the origins and elaboration of play, as is currently being advocated in the study of [ADHD]. This should be done in conjunction with studies of gene activity, particularly of the neural structures underlying the behavior patterns involved in play (pp. 381-385).” The Genesis of Animal Play: Testing the Limits, by Gordon M. Burghardt, The MIT Press, 2005 “I completely agree with Jay Feierman’s your last comment: “The issue here is human playing behavior.” Let me remind everyone that I began this focus on play because Jay did so in his edited book, The Biology of Religious Behavior, and he made statements there that I challenge. Jay said, “When behavior shows lots of variation in form when repeated by the same or different individuals, it can only be defined by its function, although its form can still be described. For example, imagine a child is ‘playing,’ which is a functional characterization of the child’s behavior. One cannot define ‘playing’ by its form because there are too many behaviors that can be used when a child is playing” (p. 75). Playing to Jay is an example of Type II Behavior, which he says cannot have a phylogeny, an evolutionary history. Jay is wrong about “playing” (importantly, he does not define “play” in his book, but was quick to challenge me to do so). Human and nonhuman play has for years been defined by its form and most researchers into play conclude that it has an evolutionary history, even though there are numerous, competing theories regarding the adapted function of play. Furthermore, the complexity and variability of the species-typical play behavior found in all juvenile mammals cannot be distinguished from human behavior on this basis, that juvenile humans show more complex patterns (or some such anthropocentric perspective). I think it is safe to say that there are innumerable videos of humans and nonhumans at play (e.g., humans, wolves, chimpanzees, and birds engaged in sensorimotor play; see below). It takes a really ethnocentric perspective to call a human 2-year old play “more complex” than that of, say, a juvenile chimpanzee or wolf (adjusting for faster development to adult stages). First, I’ll discuss play’s form. The essence of identifying an observed behavior as being play, or its definition, is this: the individual’s pattern of movement is observed to be “a 4 Play seemingly ‘non-serious’ variant of functional behavior, [that is] playful behaviors resemble serious behaviors but participants are typically more concerned with the behaviors themselves (i.e., ‘means’) rather than the function (‘ends’) of the behavior” (Pellegrini et al 2007; see link below). Here is another definition: “Play is locomotor activity performed postnatally which appears to an observer to have no obvious immediate benefits for the player, in which motor patterns resembling those used in serious functional contexts may be used in modified terms. The motor acts constituting play have some or all of the following structural features: exaggeration of movements, repetition of motor acts, and fragmentation or disordering of sequences of motor acts” (Pellegrini and Smith 2005, p. 28). The best treatment on the subject of defining play can be found in Burghardt 2005. Here is what he says: “After considering all the proposed criteria and how they might be applied to the occurrence of play in animals never considered playful (e.g., turtles), I have now decided that five key criteria are possible. It seems to me that applied in a careful manner, they can distinguish play from virtually all other phenomena with which it might be confused, including exploration and curiosity on one hand and stereotyped behavior on the other. The key here is that all five criteria have to be simultaneously satisfied for the label of play to be attached. Equally important is an additional proviso: When a criterion contains more than one attribute, only one needs to apply for the criterion to be met. 1. The performance of the behavior is not fully functional in the form or context in which it 2. 3. 4. 5. is expressed; that is, it includes elements, or is directed toward stimuli, that do not contribute to current survival. The behavior is spontaneous, voluntary, intentional, pleasurable, rewarding, reinforcing, or autotelic (‘done for its own sake’). It differs from the ‘serious’ performance of ethotypic behavior structurally or temporally in at least one respect: it is incomplete (generally through inhibited or dropped final elements), exaggerated, awkward, or precocious; or it involves behavior patterns with modified form, sequencing, or targeting. The behavior is performed repeatedly in a similar, but not rigidly stereotyped, form during at least a portion of the animal’s ontogeny. The behavior is initiated when an animal is adequately fed, healthy, and free from stress (e.g., predator threat, harsh microclimate, social instability), or intense competing systems (e.g., feeding, mating, predator avoidance). In other words, the animal is in a ‘released field.’” (pp. 69-78). Pellegrini and Smith (2005), Chapter 3, “Social Play in the Great Apes,” by Kerrie P. Lewis, p. 29 contains “Table 3.1. Ethogram of Social Play Behaviors in the Great Apes.” Play fighting, for instance (from this table), has these typical characteristics: “Aggressive movement patterns without threat gestures: wrestle; slap; jump at; jump on; play bite; cuff; pull; rough-andtumble; roll; run toward; kick; sniff; chase; attack-withdraw; spar; drag; pinch; hit.” T.M. Caro’s research on cheetah cubs (Caro 1995; see link below) contains “Table I. Behaviour patterns comprising different types of play and exploration of cheetah cubs in this study.” In that table, play is defined/categorized based upon observed patterns of behavior, such as, “bounding gait: slow run with stiff legs causing a rocking motion” (p. 335). Thus, play can and has for years been defined by its form…and this includes human animals. Chapter 4 in Pellegrini and Smith 2005 was written by Douglas P. Fry and titled 5 Play “Rough-and-Tumble Social Play in Humans.” Table 4.1. “Distinguishing Features of R&T and Aggression” is in essence an ethogram of human R&T play, a categorization along lines distinguished by motor movements. Chapters 5 and 6 cover object play, first in Great Apes and then humans. The observed patterns of behavior between humans and Great Apes are consistently the same, and, more importantly, there are important similarities in the ontogeny of the various types of play between humans and Great Apes. I already replied to your challenge, “Please give me the evolutionary history of the human game of playing chess [or basketball], which is a specific example of a non-verbal human playing.” Neither is an example of the kind of play we’re talking about, and does not fit any of the definitions of play used by serious scientists studying the evolutionary history of play. “Playing games are not included in our discussion [of play]. Games, unlike play, require participants to follow a priori rules. That is, participation in games requires participants to follow pre-set rules. If they do not follow the rules, they are penalized in some form. In play, children do follow rules, but the rules are flexible and are typically negotiated by children” (Pellegrini et al 2007). Play in human children is thoroughly discussed in Burghardt 2005. The author “amalgamates” the different categorization schemes of Piaget, Parten and Smilansky, first compiling a table and then “for each type of play, [he] also mention[s] at least one possible analogue in nonhuman play. Table 4.1. Some types of play described in human infants and children. Sensorimotor (functional or exploratory play), Construction (building, piling, stacking), Parallel (side-by-side, noninteractive), Pretend (pretense, make-believe, symbolic play), Sociodramatic (role playing, fantasy), Rough-and-tumble (R&T play, physical play), Language (babbling, repartee, jokes, humor), Rule (games with rules, either chance or skill, pairs or teams), Ritual (repetitive social routines, can include rule play)” (p. 97). I won’t belabor the point that play in human children, in both ontogeny and form, has analogues if not mirror-images in nonhumans beyond citing what Burghardt says about the first category of human play. “Nonetheless, the fact that all primates studied go through a similar series of sensorimotor (0-2 years) and preoperations (2-6 years) stages, but stop at different levels (e.g., sensorimotor stage 5 in the object permanence series in rhesus monkeys) has brought renewed respectability to aspects of the recapitulation view of play [one of the theories on the adapted function of play]” (p. 99). Where Jay goes astray is his mistaken belief that complex patterns of behavior, those that “show lots of variation in form,” and are therefore Type II Behavior cannot have an evolutionary history. Human play behavior, that is play meeting the widely-accepted definition of play (see above), is, indeed, complex and variable. Play in our closest relatives is also complex and variable. In both, however, there are consistent patterns of behavior whose form can and has been studied, with the consensus being that play has a rich evolutionary history. While studying (and continuing to do so) play behavior, I frequently run across suggestions that many observers are anthropocentric in their view of behavior. I would caution Jay that his perspective on play and complex behavior in general may also be anthropocentric. References: Burghardt 2005. Gordon M. Burghardt, The Genesis of Animal Play: Testing the Limits, MIT Press, 2005. 6 Play Caro 1995. “Short-term costs and correlates of play in cheetahs,” T.M. Caro, Animal Behavior, 1995, 49, 333-345 http://www.catsg.org/cheetah/05_library/5_3_publications/C/Caro_1995_Short_term_costs_an d_corelates_of%20play_in_cheetah.pdf Pellegrini et al 2007. “Play in Evolution and development,” Anthony Pellegrini, Danielle Dupois, Peter K. Smith, Developmental Review 27 (2007) 261-276 http://evolution.binghamton.edu/evos/wp-content/uploads/2008/11/Pellegrini01.pdf Pellegrini and Smith 2005. The Nature of Play: Great Apes and Humans, Edited by Anthony D. Pellegrini and Peter K. Smith, The Guilford Press, 2005. “In terms of play, [Tinbergen’s] four aims can be framed in the following way: What are the internal and external processes leading to performance of playful behavior? What is the ontogenetic path of play and its development in the life of the individual animal? What are the consequences to an animal of performing a given playful behavior or behavioral variant? How did play evolve from nonplay and what has been its evolutionary history? In this book, the fourth aim is the central one. The main questions are the following: Is play just a trash-can concept for a motley set of behavioral phenomena that share superficial characteristics? Do all kinds of play share common causal mechanisms deriving from common ancestors? What factors led to play becoming prominent in the lives of so many animals, yet absent in so many others? Where does playfulness first appear in animal evolution and did it evolve just once or repeatedly?” Gordon M. Burghardt, The Genesis of Animal Play: Testing the Limits, MIT Press, 2005, p. 11 “That play is a primary emotional function of the mammalian brain was not recognized until recently, but now the existence of such brain systems is a certainty. For instance, juvenile rats will exhibit roughhousing or RAT ludic behaviors (from ludare, meaning ‘to play’) even if they have been prevented from having any prior play experiences during earlier phases of development. Just as most young birds fly when the time is ripe, so do young mammals play when they have come of age. Young rats start to play around 17 days of age, and if denied social interaction throughout the early phases of psychological development (e.g., from 15 to 25 days of age), they play vigorously as soon as they are given their very first opportunity. Thus, the impulse for RAT play is created not from past experiences but from the spontaneous neural urges within the brain. Of course, a great deal of learning probably occurs during the course of roughhousing play, but this is ultimately the result of spontaneously active PLAY impulses within specific circuits of the brain, some of them in ancient parts of the thalamus, which coax young organisms to interact in ludic ways on the field of competition. I may well be that various neuronal growth factors are recruited during play, but evidence at such molecular levels of analysis remains nonexistent. Although play reflects genetically ingrained ludic impulses of the nervous system, it required the right environment for full expression. For instance, fear and hunger can temporarily eliminate play. In most mammals, play emerges initially within the warm and 7 Play supportive secure base of the home environment, where parental investment is abundant” (p. 281). Humans are a uniquely playful species. This may be due in part to the fact that we are neotenous creatures who benefit from a much longer childhood than other species. Another feature that adds to the complexity of our playfulness is the simple fact that our play instincts are modified so markedly by our cognitively focused higher brain areas. Although cortical processes surely add a great deal of diversity to our playful behaviors, especially as we develop, it is unlikely that the primal brain ‘energy’ for playfulness emerges from those higher brain functions. These energies probably emerge from the same ancient executive systems that govern that govern RAT play in other species. As those primitive playful impulses percolate through the brain, they assume new forms ranging from slapstick humor to cognitive mirth. Indeed, the hallmark of PLAY circuitry in action for humans is laughter, a projectile respiratory movement with no apparent function, except perhaps to signal to other one’s social mood and sense of carefree camaraderie” (p. 287). Jaak Panksepp, Affective Neuroscience: the foundations of human and animal emotions, Oxford U. Press, 1998 “The central argument of this biological book on play behavior may be summarized, briefly and simply as follows. Animals risk time, energy, and injury to play. They do so in certain environments and because play is important for development in those environments. Play is a behavioral mediator between the environment and the phenotype. Through play, the cerebral cortex is stimulated to grow, to develop, and therefore to take a larger role in control of behavior, making that behavior more flexible. Simultaneously, play experience produces adaptive modifications of effector structures, such as muscle, bone and connective tissue, used in that behavior. Through play, animals acquire physical ability and develop social relationships. Such plasticity evolved because of economic tradeoffs in brain development: the optimal balance between cortical and subcortical control of behavior depends on environmental information, and the experience of play reliably serves to indicate that the animal is in an appropriate environment for such responses to develop, as well as to develop the responses themselves, and anatomical structures that support them, through repetition and variation. How can such behavior evolve when the plasticity underlying the effects involved is subject to manipulation by others in the service of their own selfish interests, which may not coincide with those of the subject? The probable answer to this question of evolutionary stability is that play occurs under circumstances in which current or future resources cannot be competed for in this way; that such damaging behavior would be costly to the actor as well as the recipient and therefore generally evolutionarily unstable against a strategy of not playing at all; that social play is designed to include only messages that cannot be faked or only stimuli that cannot be successfully manipulated to damage another; that developmental resilience, including the ability to detect and resist attempts at damaging manipulation through play, holds such damage to an evolutionarily tolerable (though not necessarily negligible) level; and that social play evolved through kin selection, with close kin favored as playmates, making cheating even less likely given the conditions for play already described above (pp. 19-20). 2. Defining play. Like other coarse-grained behavioral categories, including aggression and even sex, play is difficult to define. ‘Play’ is a convenient, but scientifically inexact term used to denote certain locomotor, manipulative, and social behaviors characteristic of young (and of some adult) mammals and birds under certain conditions in certain environments. The term 8 Play ‘play’ may be defined structurally or functionally. It may refer to a category of behavior, to a behavioral or social relationship, or even to a mental state. Play can be a theoretical extreme point of an abstract continuum whose opposite extreme is agonistic, predatory, or predator avoidance behavior. The scientific study of play consists of a set of behavioral descriptions and a set of theoretical, observational, and experimental investigations of the behaviors described, including causation, results, and correlates. For the purposes of this book, play includes nonagonistic fighting and chasing maintained by social cooperation; solo locomotor and rotational movements performed in the absence of threatening predators, parasites, and conspecifics; developing locomotor or manipulative behavior repeated with slight variation at a previously established level of mastery; and diversive effector interactions with an inanimate object subsequent to the termination of an initial phase of sensory and mastery activity, including exploratory manipulation, directed toward the object. These behaviors are the outward expressions of a set of distinct, but functionally related developmental pathways that may run parallel to each other, merge, or branch. Therefore, the distinctness (by any arbitray criterion) of these categories of play may depend on the species, sex, and developmental state of the individual studied (p. 21). 4. Continuity. The natural history of play in mammals and birds is remarkably uniform. When compared across species, behavioral content and structure of play appear to vary little if at all around norms of nonagonistic contact, including wrestling or sparring, or nonpredatory locomotion and body rotation, including pursuit, capture, handling, and evasion. Most differences in play behavior between species mirror behavioral, demographic, anatomical, or environmental constraints. However, complexity or elaborateness of play appear to increase with relative brain size across a wide phylogenetic spectrum” (p.22). Robert Fagan, Animal Play Behavior, Oxford U. Press, 1981 9