Play and Its Role in Behavioral and Brain Development in Animals and HumansPresentation Transcript
If it was as much fun to study play as it is toengage in it, more would be known about theactivity.At this point little can be said about theevolution of horse play or even how it differsfrom play in other orders of mammals.However a number of important studies of playhave been published which support the role ofplay as an important factor in understanding theevolutionary and adaptive behavior of somespecies, including the horse. These studiescarried byanthropologist, neurobiologist, evolutionist, biologist, ecologist, neurologist, psychologist andother scientist allow us to gain someunderstanding of play in intra and inter-specificinteractions.
Is play essential to development?Is it the driving force behind human and animal behavior?Some scholars have called play undefinable, nonexistent, or a mystery outside the realmof scientific analysis.Although playfulness may have been essential to the origin of much that we considerdistinctive in human and mammalian behavior, it only develops through a specific set ofinteractions among developmental, evolutionary, ecological, and physiologicalprocesses.Play is the biological equivalent of a luxury item, the first thing to go when an animal or achild is hungry or sick.Furthermore, play is not always beneficial or adaptive.For example 80% of deaths among juvenile seals occur because playing pups fail to spotpredator approaching. It is also extremely expensive in term of energy. Playful animalsuse around 2 or 15 % of their energy cavorting. For evolutionary biologists even 2 or 15% is huge - you just don’t find animals wasting energy like that, there must be a reasonfor this dangerous activity. But if play is not simply a developmental hiccup, as biologistsonce thought, why did it evolve?One of the most popular explanations of play is that it helps juveniles develop the skillsthey will need to hunt, mate and socialize as adults. Another is that it allows younganimals to get in shape for adult life by improving their respiratory endurance. Boththese ideas have been questioned in recent years.
One of the most popular explanations of play is that it helps juveniles develop the skillsthey will need to hunt, mate and socialize as adults. Another is that it allows younganimals to get in shape for adult life by improving their respiratory endurance. Boththese ideas have been questioned in recent years.Take the exercise theory. If play evolved to build muscle or as a kind of endurancetraining, then you would expect to see permanent benefits. But Byers points out that thebenefits of increased exercise disappear rapidly after training stops, so any improvementin endurance resulting from juvenile play would be lost by adulthood . "If the function ofplay was to get into shape," says Byers, "I would expect the age distribution of play tovary widely." The optimum time for playing would depend on when it was mostadvantageous for the young of a particular species to get in shape. But it doesnt worklike that. Across species, play tends to peak about halfway through the suckling stageand then decline to a low at weaning.Then theres the skills-training hypothesis. At first glance, playing animals do appear tobe practicing the complex maneuvers they will need in adulthood. But a closerinspection reveals this interpretation as too simplistic. In one study, behavioral ecologistTim Caro from the University of California looked at the predatory play of kittens andtheir predatory behavior when they reached adulthood. He found that the way the catsplayed had no significant effect on their hunting prowess in later life.
In another study, neuroscientist Sergio Pellis of the University ofLethbridge in Alberta, Canada, scrutinized videos of rodents play fighting--the most common form of social play in rodents. Despite superficialsimilarities between this and the social, sexual and fighting behavior ofadult animals, Pelliss close examination of the play bouts revealed nocompelling link between play maneuvers and adult tactics. "For rats, andprobably other rodents," says Pellis, "the primary function of play fightingdoes not appear to be to provide practice for either sex or aggression."
So what is going on, why play?People have not paid enough attention to the amount of the brain activated by play says MarcBekoff from the University of Colorado. The idea is backed up by the work of neuropsychologistStephen Siviy of Gettysburg College in Pennsylvania. Siviy studied how bouts of play affect thebrains levels of a protein called c-FOS--a substance associated with the stimulation and growthof nerve cells. He was surprised by the extent of the activation. "Play just lights everything up,"he says. He speculates that by allowing connections between brain areas that might notnormally be connected, play may be enhancing creativity.All these findings paint a picture of how play might have originated. The comparative studyreported earlier this year by Pellis and his colleagues suggests a "stepwise" relationship betweenincreasing brain volume and the evolution of play. The researchers suggest that minor changesin brain size might not have required evolutionary changes in play behavior, but at certainthreshold increases in volume, greater levels of playfulness evolved.
Behaving this way activates many different parts of the brain it is like a behavioral kaleidoscope,with animals at play jumping rapidly from one activity to another. They use behavior from a lotof different contexts--predation, aggression, reproduction their developing brain is getting allsorts of stimulation.Not only is more of the brain involved in play than was suspected, but it also seems to activatehigher cognitive processes. Theres enormous cognitive involvement in play because play ofteninvolves complex assessments of playmates, ideas of reciprocity and the use of specializedsignals and rules, play creates a brain that has greater behavioral flexibility and improvedpotential for learning later in life. Its about more connectedness throughout the brain.Play might be related to growth of the cerebellum, since they both peak at about the same time,there is a sensitive period in brain growth during which time it’s important for an animal to getthe brain-growth stimulation of play to achieve its ultimate configuration, think of the relativeease with which young children-but no infants or adults absorb language. This is a signature of a‘’sensitive period’’ – a brief developmental window during which the brain can be modified inways that are not easily replicated earlier or later in life. In almost every species studied, a graphof playfulness looked like an inverted ‘’U’’ increasing during the juvenile period and then fallingoff around puberty, after which time most animal don’t play much anymore. In human the peakperiod is between the ages of 1 to 4.
Play just light everything up by allowing connections between brain areas that might notnormally be connected, play may be enhancing creativity, and in other words, playing makesyou intelligent.Prompted by the observation that play seems confined to the most intelligent animals, Byerslooked at the behavior and brain size of various marsupials. He found that playful species suchas the wombat have bigger brains for their body size compared with their lazier kin, whichinclude the docile koala. More recently, Pellis has teamed up with Andrew Iwaniuk of MonashUniversity in Melbourne to show that in primates, the amount the brain grows between birthand maturity reflects the amount of play in which each species engages.And earlier this year, Pellis, Iwaniuk and biologist John Nelson, also of Monash University,reported that there is a strong positive link between brain size and playfulness for mammals ingeneral. It is the most extensive quantitative comparative study of juvenile play ever published.Comparing measurements for 15 orders of mammals--from canids to dolphins, rodents tomarsupials--the team found larger brains (for a given body size) are linked to greater levels ofplay. Likewise, animals with relatively small brains tend to play less.
Play has traditionally been classified into three basic categories:- Object play, which involves the manipulation of inanimate things.- Locomotors play, which consists of activities such as running and rotational body movements. - Social play, which involves two or more individuals that respond to each others actions.(Fagen 1981)There has been some movement in the literature to try to consider these types of playseparately because they develop at different times in ontogeny (Gomendio1988) and appear todiffer in their motivational basis (Pellis 1991). Furthermore, some of the explanations offered forplay pertain only to social play (e.g., social bonding, Carpenter 1934). This approach at firstseems very attractive because it subdivides an unwieldy research topic into smaller, seeminglymore manageable units. However, some descriptions of play suggest that object, locomotorsand social variants form a single natural category. First, different types of play tend to beinterspersed within the same play.
Lewiss recent findings point to the intriguing possibility that different types of play may haveevolved at different stages in evolutionary history, to allow the development of distinct regionsof the brain.She looked at the relative size of the neocortex--which is responsible for social reasoning,among other things--in primate species, and found that the larger the neocortex in each species,the more social play they indulged in. But this relationship did not extend to object or motion-based play. By implication, Lewis believes, social play may help wire up the social brain, whileother forms of play do not. "I think its reasonably safe to assume that different types of play didemerge at different points in time, but possibly with some overlap," she says.The idea that play has evolved to build big brains certainly has its critics. Like much of behavioralecology, it rests on a scaffolding of correlations. "The problem with correlations is that theydont consider unknown third variables," cautions Caro. "So maybe brain size and play are bothcorrelated with metabolic rate or some other factor? Certainly, something about being [warm-blooded] seems important for promoting play."Even some of the researchers whose results seem to support the link between brain buildingand play are cautious in their assessment of the theory. Siviy believes there is not yet enoughevidence to settle the question. But he thinks the timing of play is convincing. "Its an ideal timeto do some learning, to make some modifications to brain circuitry," he says.One of the strengths of the idea is its testability. Magnetic resonance imaging techniques thatidentify myelin by-products, for example, should be able to show whether play boostsmyelination, as Lewis has suggested. Whats more, measuring the volume and activity of certainparts of the brain is becoming increasingly easy due to advances in non-invasive imaging.If the theory is backed by experiment, what would it say about the way many of us in affluentsocieties raise our children? We already know that rat pups denied the opportunity to play growsmaller neocortices and lose the ability to apply social rules when they do interact with theirpeers.
Discussions about play force us to reckon with our underlying ideas about childhood, sexdifferences, creativity and success. Do boys play differently than girls? Are children beingdamaged by staring at computer screens and video games? Are they missing something whenfantasy play is populated with characters from Hollywood’s imagination and not their own?Most of these issues are too vast to be addressed by a single field of study. But the growingscience of play does have much to add to the conversation. Armed with research grounded inevolutionary biology and experimental neuroscience, some scientists have shown themselveseager — at times perhaps a little too eager — to promote a scientific argument for play. Theyhave spent the past few decades learning how and why play evolved in animals, generatinginsights that can inform our understanding of its evolution in humans too. They are studying,from an evolutionary perspective, to what extent play is a luxury that can be dispensed withwhen there are too many other competing claims on the growing brain, and to what extent it iscentral to how that brain grows in the first place.
Scientists who study play, in animals and humans alike, are developing a consensus view thatplay is something more than a way for restless kids to work off steam; more than a way forchubby kids to burn off calories; more than a frivolous luxury. Play, in their view, is a central partof neurological growth and development — one important way that children build complex,skilled, responsive, socially adept and cognitively flexible brains.Their work still leaves some questions unanswered, including questions about play’s darker,more ambiguous side: is there really an evolutionary or developmental need for dangerousgames, say, or for the meanness and hurt feelings that seem to attend so much child’s play?Answering these and other questions could help us understand what might be lost if childrenplay less.
Fagen, R. 1981. Animal Play Behavior. New York: Oxford University Press.Gomendio, M. 1988. The development of different types of play in gazelles:implications for the nature and functions of play. Anim. Behav., 36,825-36.Pellis, S. M. 1991. How motivationally distinct is play? A preliminary casestudy. Anim. Behav., 42, 851-3.Carpenter, C. R. 1934. A field study of the behavior and social relations ofhowling monkeys.Animal Play by Marc Bekoff and John Byers, Cambridge University Press (1998)"Do big-brained animals play more?" by Andrew Iwaniuk, John Nelson and Sergio Pellis, Journalof Comparative Psychology, vol 115, p 29 (2001)Tom Schierlitz The New York TimesThe National Institute for Play Stuart BrownThe Genesis of Animal Play Gordon Burghardt