FOREWORD
Play, broadly conceived, may be a major process underlying lives worth living. (Location 111)
salud mental cita juego favorite
Readers will need to uncover their own nuggets, sometimes scraping through the modest overlay in which Serge and Vivien embed them. These nuggets need to be amalgamated, however, to appreciate how these rich empirical data not only extend, but actually refocus, our understanding of how play evolves across species, develops in individuals, and functions in real life. They do this by carefully describing the details of play in many species and analyzing the neural, hormonal, and other physiological and sensory systems underlying play. (Location 124)
Educators, therapists, anthropologists, sociologists, recreation supervisors, and psychologists studying play have ignored the vigorous rough-and-tumble play focused on here, while biologists and ethologists rarely connect their studies on play in non-human animals with the rich literature on children. (Location 129)
Social play turns out to be a phenomenon with both a deep and shallow evolutionary history. That is, while play fighting may go back in evolutionary time to fish and amphibians, its manifestation in monkeys, rodents, canids, seals, ungulates, and other groups is highly variable. This can only mean that play has functions in animal lives that vary even among closely related species. (Location 147)
PREFACE
cross-cultural studies show that play by children can be valued, merely tolerated, or actively discouraged. (Location 163)
Unfortunately, because the field of animal behavior did not fully emerge as an independent, academic discipline until the middle of the twentieth century, much of the research on non-human animal play was sporadic, and many of the reports on the subject were buried in broader behavioral and ecological studies of animals. Despite this problem, research on non-human animal play began to pick up steam in the 1970s and became a legitimate problem worthy of broad attention in the early 1980s, as a result of the publication of two seminal works. (Location 172)
The lack of success by the first approach in identifying an empirically, well-supported function for play and the accumulation of interesting, but disparate facts, by the second approach, led to the waxing and waning of interest by researchers in studying non-human animal play. (Location 190)
Thus, play remains a problem that needs an explanation, and one way in which its study can progress is to combine the approaches that emphasize function with those that emphasize mechanism. What is needed is an overarching theoretical framework for play that can embrace them both. (Location 193)
Readers should also be aware that this book is not just a summary of what is known. Rather, we utilize our own journey in empirical research on play as a guiding framework within which to incorporate and evaluate what has been uncovered by dozens, if not hundreds, of researchers around the world. Thus, we view this book as a synthesis of what we have learned personally, and have offered here many new insights about how play originated, evolved, and has come to have the properties it does in some marvelous players such as rats and humans. (Location 222)
1 THE PUZZLE OF PLAY
So what are the characteristics that define behavior as play? Historically, defining play has not been an easy task, and there is no single agreed-upon definition. Nevertheless, there are criteria that most researchers generally agree to be necessary components of a definition of play: it is an activity that is engaged in voluntarily, and it is positively reinforcing – that is, the performers find it pleasurable. Although these two criteria are true of other behaviors, such as eating and sex, another commonly incorporated criterion is that the purpose of play is not immediately utilitarian. This feature of play is often critical, since for non-human animals, play is often a simulation of a functional activity, such as fighting or predation. Thus, it is the absence of the normal consequences of these behaviors – the killing and eating of prey or the taking of food or some other resource from a social partner – that alerts the observer to the possibility that the behavior being observed is play. (Location 459)
Therefore, in most cases, we rely on our intuition to distinguish between play and non-play. (Location 471)
when studying human play, subjects that are engaging in either playful or serious fighting can, of course, be asked as to whether their behavior was playful or serious, so as to verify the judgments of the observers that are based on the behavioral cues alone. (Location 481)
Gordon Burghardt has developed a set of criteria that must be met for an instance of behavior to qualify as play: (1) that the behavior is incompletely functional in the context expressed; (2) that it is voluntary; (3) that it is, in some ways, structurally modified or temporally shifted as compared to when it is used in its normal, functional context; (4) that it is performed repeatedly, but not necessarily in an invariant form; and (5) that it is present in healthy, unstressed animals. In using these five criteria, researchers have shown that animals as diverse as turtles, wasps, and octopuses engage in behavioral sequences that are comparable to those performed by mammals such as dogs and monkeys – ones to which most observers would happily apply the label of play. (Location 489)
Based on studies of both free-living and captive animals, play occupies up to 20% of an animal’s daily time budget and up to 10% of their daily energy budget. Given that these figures are for animals in their juvenile period, this implies that these individuals are sacrificing resources that could be channeled into growth. Furthermore, when playing, animals risk making themselves conspicuous to predators and chance injury. Although there is debate about how significant a burden these costs may actually be, there is little doubt that play involves some cost, such as spending less time feeding, and so must also have some compensating benefits – even if these benefits are modest in magnitude. (Location 498)
Like all biological traits, play has evolved, and evolution is a messy process. The origin of traits need not reflect their current functions, and traits used for one function at a particular time may be co-opted for another function at another time. (Location 511)
It is this complex tapestry created by millions of animals evolving over vast periods of time that causes us to stumble when we try to encapsulate these diverse patterns and processes into a single definition or explanatory theory of play. But this very richness in variation is also an advantage. Nature has provided us with a vast array of natural experiments, with different lineages of organisms having changed play in this way or that, which allow us to exploit this variability as a useful tool for research. (Location 521)
In the comparative literature, play fighting, or rough-and-tumble play, is the most commonly reported form of play. And, within that literature, the most detailed and extensive experimental research has focused on laboratory rodents, with the rat being especially prominent. (Location 529)
So, the first task of the comparative analysis that we use here is to chart the pathway by which a particular species has come to acquire its unique characteristics of play fighting. (Location 538)
rats without a cortex (decorticate) are still able to use all the behavior patterns typical of play fighting and to engage in such play just as frequently as rats with intact brains. Consequently, decorticate rats not only want to play, but also know how to play. However, when they play, their behavior is not without abnormalities. These rats fail to modify how they play at different ages; rather, at all ages, they play in the same manner. Nor do they modify their play when interacting with different partners – they play in the same manner whether their partner is a dominant male, a subordinate male, or a female. Furthermore, these age-related and partner-related modifications in play fighting involve different neural circuits in the cortex, as we will explain in greater detail in a later chapter. (Location 552)
A Cause for Rejoicing and A Cause for Caution
while we know quite a lot about laboratory rats, laboratory mice, and a few other rodents, our knowledge of these species under more natural conditions is limited. (Location 572)
In addition to these concerns is the fact that the principal subject in our story, the laboratory rat, has been domesticated for over 100 years. After so many years of selective breeding, it is likely that the behavior of domesticated rats bears little resemblance to that of their wild counterparts.17 These concerns about the validity of using the rat as a model for piecing together the evolutionary pathways by which play fighting has been transformed into a complex behavior that serves multiple functions, have to be taken seriously. However, we will show that, with suitable caution, the model that we are proposing can usefully guide us in making play a more comprehensible phenomenon. (Location 574)
Although few studies have explicitly compared domesticated rats to their wild counterparts, those that have indicate that the behavior of wild and domesticated rats is comparable both in terms of their social affinities and their basic repertoire of behavior patterns. (Location 587)
No doubt some of the details in the patterns of their respective play fighting may differ, but the broad outlines are likely to be similar. (Location 592)
By characterizing different grades of organization – from simple to complex – we can direct our attention to the brain by asking what changes in brain function would be needed to enable a change in the complexity of play. By taking a brain’s eye point of view, we ensure that changes in behavior are grounded in concrete changes in the organ most responsible for that behavior. (Location 594)
What Do Rats Do When Play Fighting?
By engaging in play fighting, both juveniles and adults can regulate their stress response. That is, by playing, the animals can calm themselves following a frightening, but not too frightening, experience. In addition, male adult rats use play fighting as a means of social assessment and manipulation in the context of dominance relationships. Thus, in at least two ways, play fighting provides the rats with immediate benefits. (Location 674)
experience in play fighting in the juvenile period modifies the brain areas involved in social competence. Play fighting thus serves a delayed benefit. A comparison with non-rodent species, especially primates, suggests that both these immediate and delayed benefits may be available to a range of animals, including humans. (Location 680)
if people are like rats, the current trend in much of the Western world for zero-tolerance of rough-and-tumble play among children is not doing upcoming generations any favors as to the development of their social competence. (Location 684)
we also conclude that no theory to date can account for all the features observed in the play of animals. (Location 692)
2 THE PLAYFUL RAT
Whether nuzzled by another rat or tickled by a familiar experimenter, rats appear to enjoy the experience – they will briefly tolerate the contact and run away but then come back for more. Furthermore, when undergoing such an experience, they emit an ultrasonic call akin to human laughter and their brains release neurochemicals associated with pleasure.3 So, it seems that being playfully nuzzled is an enjoyable experience and must be the engine that drives rats to want to play. But what does the rat doing the nuzzling gain? (Location 706)
if play-deprived rats are re-housed with a partner that has been chemically treated so that it is active, but non-playful, the untreated animal will still run up to its partner and contact its nape at a heightened frequency.5 Even without a playful response by the partner, gaining access to the nape and nuzzling it seems to be rewarding in itself. If we return to our tickling example, tickling someone else seems to be just as pleasurable as being tickled. So, both giving and receiving nuzzling likely taps into the same pleasure system that is engaged by tactile contact. (Location 718)
After prolonged exposure to a drugged rat that does not resist having its nape contacted, an attacker finds the experience disconcerting. It will even begin to dig at the substrate, which is an anti-predator behavior often used by rats in anxiety-inducing situations.7 Thus, the lack of a suitable response from its playmate appears to distress a rat. Therefore, while nuzzling the nape of another rat is rewarding, some active resistance to such contact by the recipient of that nuzzling makes it even more so. (Location 724)
play fighting is a combination of competition and cooperation. (Location 733)
those individuals with whom gaining the advantage was a challenge, but who did not make it impossible for you to win, were likely the ones with whom you played most often. (Location 735)
in 80% or more of attacks, the recipient performs some defensive action. (Location 745)
The Development of Play Fighting
Was it Good for You, Big Boy?
for many species, the body targets competed over during serious fighting and play fighting are the same.14 Rats, however, appear to be an exception to this general pattern. (Location 817)
neither the offensive nor the defensive targets present in serious fighting are contested during play fighting. (Location 821)
From such wide-ranging, comparative analyses, we can conclude that play in general, and play fighting in particular, must have evolved multiple times. That is, when certain enabling conditions coalesce, playful behavior emerges. (Location 2927)
In playful species from many lineages, some have retained play fighting into adulthood and have co-opted it for use as a means of social assessment and manipulation. (Location 2939)
The Uses of Ambiguity
Like adult rats, many species of mammals, including greater bush babies, common marmosets, slow loris, and New World deer, use play fighting to establish and maintain social bonds and, again, like rats, many species, including chimpanzees and Old World deer, use play fighting to test existing or emergent relationships. (Location 2983)