Michael Irey climbs while Javas Campbell jumps from the top of the climbing wall at the Lehi Outdoor Pool on Saturday, August 13, 2011.

Brook Monroe Hopkins stands by the aqua climb. Staff photos by John Mullen

A water aerobics class works out in front of the aqua climb wall.

These categories support previous research on children’s play in general and risk- taking play in particular (Aldis, 1975; Blurton Jones, 1976; Humphreys and Smith, 1984; Kaarby, 2004; Smith, 1998; Stephenson, 2003).

Using a modular perspective based on Sandseter’s (2007a, 2007b) six categories, each  type  of  risky  play  will  be  considered  separately.  Sandseter’s  (2007a)  interviews revealed that some of the categories were perceived risky by both children and staff (great heights, high speed and rough-and-tumble play), while others were unanimously perceived risky only by the staff (dangerous tools and dangerous  elements), and still others were perceived risky only by the children (danger of disappearing/getting lost). This is in accord with the concepts of mismatch (Nesse and Williams, 1995) and hypophobia (Marks and Nesse, 1994) as previously mentioned. The relative stability of our evolved psychology and the rapid progress of socio-cultural development have led to the fact that not all dangerous items  or  situations  elicit  fear  or  anxiety  reactions  (Kennair,  2007).  In  addition  the perception  of what  is  risky  or  not  may  be  due  to  individual  genetic  differences  and environments (Kendler et al., 2002) as well as experience and  habituation (Poulton and Menzies, 2002a, 2002b). In the following, the categories of risky play perceived as risky and thrilling by the children will be addressed first, followed by the categories perceived risky only by the staff (in this sense, caregivers). Each of the categories will be discussed in relation to possible functions and anti-phobic effects.

Play with great heights
The most frequent form of risky play in great heights is climbing. Children climb on all climbable features, such as trees, playground climbers, big rocks, steep slopes, hillsides, etc. Jumping down from high places, incidents of hanging or dangling from heights and balancing close to drops are also common  kinds  of play with great heights (Sandseter, 2007a, 2007b).

Possible functions.  Benefits of this kind  of play  may  be  to  get  to  know ones ecology, exploring the environment (Bjorklund and Pellegrini, 2002) and practicing and enhancing  different  motor/physical  skills  for  developing  muscle  strength,  endurance, skeletal quality, etc. (Bekoff and Byers, 1981; Bjorklund and Pellegrini, 2000; Byers and Walker, 1995; Humphreys and Smith, 1987;  Pellegrini and Smith, 1998). All physical practice and training might be relevant for the developing child. Play in great heights also involves training on perceptual competencies such as depth-, form-, shape-,  size-, and movement perception (Rakison, 2005), and general spatial-orientation abilities (Bjorklund and  Pellegrini,  2002).  These  are  important  skills  both  for  survival  in  childhood  (i.e., immediate benefits) and for handling important adaptive tasks in adulthood (i.e., deferred benefits).

Although  not  describing  in  detail  the  behavior  patterns  of  the  play,  many ethnographic  studies  provide  evidence  for  locomotor  play  such  as  chasing,  running, climbing, jumping down,  sliding, swinging and different forms of acrobatics in a wide range of hunting-and-gathering and agricultural village cultures throughout the world (see, e.g., Gosso, Otta, Morais, Ribeiro, and Bussab,  2005; Power, 2000; Smith, 1982, 2005). Further  strengthening  the  evolutionary  explanation,  locomotor  play  similar  to  human locomotor play is also found among non-human mammals (e.g., primates, carnivores) and some kinds of birds (Aldis, 1975; Power, 2000; Smith, 1982). Aldis (1975) also shows that an important aspect of this kind of play in both animal and human groups is seeking out thrills  and  slightly  fearful  situations  related  to  height,  speed,  daring  movements  and unpredictable outcomes of the play.

Anti-phobic effect. According to Poulton and Menzies (2002a, 2002b) one might expect the fear of heights to develop naturally. Contrary to earlier theories claiming that fear of heights  was due to serious accidents, Poulton et al. (1998) found that children sustaining injury due to falls both before age 5 and between ages 5 and 9 did not have a greater frequency of fear of heights at  age 11  and  height  fear and phobia at  age 18. Interestingly, injurious falls from heights between ages 5 and 9 were associated with the absence of height fear at age 18, thus indicating an opposite direction than that predicted by conditioning, and providing strong support of a non-associative theory of fear acquisition in the development of a fear of heights (Poulton et al., 1998). Those who have fear of heights at low age usually avoid heights, while those who have a low level of fear of heights are more likely to engage in risky behavior near heights, thus experiencing more serious falls. Risky play with great heights will provide a  desensitizing or habituating experience and maturationally adequate mastery providing cognitive restructuring. This will result in less fear of heights later in life.

Play with high speed
Swinging  with  high  speed,  riding  a  bike  at  high  speed,  running  at  high  and uncontrolled speed, or sliding down slides, hills, cliffs, etc. are common forms of this category of risky play. Sandseter (2007a, 2007b) discovered that children often increased the risk of swinging by standing  on the swing, swinging several children together or in other challenging ways, or in sliding down snowy slopes by throwing themselves on their stomachs head first, backwards, or several children in a row, etc.

Possible functions. The most obvious evolutionary function of play in high speed is the enhancement of perception – particularly depth – and movement perception, but also the perception of size and shape (Rakison, 2005). Another obvious benefit of high speed activities such as swinging and sliding is training on spatial-orientation abilities (Bjorklund and Pellegrini, 2002). Also, the more general physical and motor stimulation of play where children move around running, bicycling, walking up and  sliding down hills or slides, enhances their physical fitness and motor competence (Bekoff and Byers, 1981; Bjorklund and Pellegrini, 2000; Byers and Walker, 1995; Pellegrini and Smith, 1998).

The aforementioned documentation on locomotive play such as chasing, running, sliding and swinging found both in different human cultures across the world as well as in non-human  mammals (see, e.g., Gosso et al., 2005; Power, 2000; Smith, 1982; Smith, 2005) applies to the evolutionary argument of the function of play with high speed.

Anti-phobic effect. This kind of play might be motivated by mechanisms that were necessary for our tree-dwelling ancestors to be motivated to swing from tree to tree. The result of this  behavior may be a greater chance of falling and hurting oneself, but at the same time the behavior will decrease the chance of developing anxiety of heights and also fear of emotional activation in general.

High speed was not a typical part of our hominin ancestors’ ecology. There are therefore no obvious hominin adaptations for high speed. Thus it seems more likely to be more archaic or due to by-products of perceptual systems. Still, the anti-phobic effects of feeling  the  thrill  and  excitement,  as  well  as  associating  physiological  activation  with positive experiences and emotions, ought to be assessed in further research.

Rough-and-tumble play
Typical  activities  in  this  category  of  risky  play  are  fighting,  fencing  with sticks/branches, play wrestling and chasing (Blurton Jones, 1976; Humphreys and Smith, 1984; Sandseter, 2007a, 2007b; Smith, 2005).

Possible functions. Rough-and-tumble play is the most common form of play in non-human  mammals (Aldis, 1975; Bekoff and  Byers, 1981; Fry, 2005; Power, 2000; Smith, 1982), and it is also found, not only in Western industrialized cultures, but in a wide range of other cultures such as hunting-and-gathering and agricultural village cultures all over  the world  (see,  e.g.,  Fry,  2005; Gosso  et  al.,  2005; Power, 2000; Smith,  2005). Research  on  rough-and-tumble  play  in  both  animals  (e.g.,  primates,  carnivores)  and humans have also found that males engage more in play-fighting than females (Aldis, 1975; Bjorklund and Pellegrini, 2002; Power, 2000; Smith, 1982; Smith, 2005) and that  the roughness in the play seems to increase with age (Power, 2000).  The findings that rough- and-tumble play  such as play-fighting is common across cultures and animals similar to humans support the suggestion that this kind of play is a result of an evolutionary adaptive process.

Rough-and-tumble play  involves  great  physical  and  motor  stimulation,  and  the functions,  both  deferred  and  immediate, of physical training  through play activities  is addressed  above.  Another  possible immediate function of rough-and-tumble play is to enhance complex social competences such as affiliation with peers, social signaling, good managing  and  dominance  skills  within  the  peer  group,  bargaining,  manipulating  and redefining situations (Flinn and Ward, 2005; Humphreys and Smith, 1987; Pellegrini and Smith, 1998; Smith, 1982).  According to  Bjorklund and  Pellegrini (2000), rough-and- tumble  play  also  serves  deferred  benefits  by  enhancing  survival  and  reproduction, particularly for boys – who most often engage in this kind of play, of gaining competence in aggression, fighting, social  competition and experience in dominant and subordinate roles. These are social competencies that are useful for adult life and evolved strategies for enhancing survival, as males have had to face competition, dangers and physical challenges as hunters (Jarvis, 2006). For kindergarten children there rarely is an aim to hurt the other and both parts partake in this as a playful activity (Humphreys and Smith, 1987). Still, research  suggests  that  rough-and-tumble  play  in  preschool-  and  primary  school-aged children provides  practice and  hones skills  for regulating aggressive behavior (Dodge, Coie,  Pettit,  and  Price,  1990).  Studies  of  peer  perception  found  that  non-aggressive cooperative children were liked by peers and that bullies were disliked by peers (Boulton and Smith, 1994, 1996; Dodge et al., 1990), and that physical aggressive behavior among boys  may  continue  into  adolescence  (Broidy et  al.,  2003;  Scholte,  Engels,  Overbeek, Kemp,  and  Haselager,  2007).  Not  being  able  to  regulate  aggression  and  real  hostile behavior in rough play situations is therefore disadvantageous for the social development of a child.

It is worth noting that dominance in rough-and-tumble play becomes even more obvious as one enters adolescence (Humphreys and Smith, 1987; Smith, 1997). As the boys, as is most  often the case, move toward puberty the roughhousing becomes more competitive  and  the  weaker   fighter  will  be  dominated  by  the  stronger  fighter.  The roughhousing thus changes character and function and becomes more a hierarchy building activity.

Rough-and-tumble play thus seems to have important functions, both immediate and deferred, for motor practice, social skills practice, aggression regulation and physical health.

Anti-phobic effect. The anti-phobic effect  of rough-and-tumble play is not  very evident, and there is a lack of research looking into this issue. It might be that this is not a relevant  function of this kind of play. Still, a couple of researchers have outlined the possibility that rough-and-tumble play, particularly the kinds where the participants aim to scare each other by taking the role as monsters or other scary creatures, the kinds where war-play  is  the   essential  focus,  and  the  kinds  including  unpredictable  and  sudden movements and high sounds, can be a form of play-fear reinforcement that can reduce anxiety  by  habituation  in  a  pretend  situation  (Aldis,  1975;  Power,  2000).  One  might speculate that social phobia and other forms of anxiety involving social hierarchy, physical closeness  and   social  evaluation  (i.e.,  fear  of  people)  might  be  reduced  due  to  a normalization of the intimacy and self-assertion involved in normal rough-and-tumble play. Organized rough and tumble play, such as Judo  practice, has been researched and some findings suggest that children become less aggressive, less emotionally disturbed and less anxious through such practice (Gleser and Lison, 1992; Lamarre and Nosanchuck, 1999).

Play where the children can “disappear” / get lost
Both Sandseter (2007a) and Davidsson (2006) have found that children love to walk off alone and go exploring away from the eyes of adults. Children experience a feeling of risk  and  danger  of getting  lost  on occasions where they are given the opportunity to “cruise” on their own exploring unknown areas; still, they have an urge to do it (Sandseter, 2007a).

Possible  functions.  The  urge  to  walk  off  alone  in  new  and  undiscovered environments without supervision from adults is children’s way of exploring their world and becoming at  home in it (Bjorklund and Pellegrini, 2002; Smith, 1998). Research has shown that exploration is an important part of children’s play (Davidsson, 2006; Kaarby, 2004; Sandseter, 2007a). According to Bjorklund and Pellegrini (2002), the fact that boys engage more than girls in exploration, and also explore larger areas than girls, is related to what Bowlby called the environment of evolutionary adaptedness (EEA) where males were hunters and had to be able to  safely move around in diverse and large areas away from home. This is in accordance with the research  of Silove, Manicavasagar, O’Connell and Morris-Yates (1995) arguing that a lower level of separation anxiety among boys than girls is due to the adaptive pressure for boys to learn hunting skills and the courage to venture far from the home, and opposite for girls to learn skills for nurturing and creating  safe environments for child-rearing. Enhancing perceptual competencies such as depth-, form-, shape-, size-, and movement perception is also a natural function of children’s exploration of their environment (Rakison, 2005).

Studying animal and human play, Aldis (1975) makes a distinction between serious exploration where the human/animal learns about their environment, and play which is just playful activity. Aldis  describes serious exploration with the example of a young rhesus monkey that first independently leaves its mother to explore the immediate proximity, and at the first sign of danger will flee back to her. Then,  over a period of time, the young rhesus monkey will gradually fan out from “home base” to explore more distant areas.

Aldis argues that through serious exploration, rather than play, animals learn what features of the environment lead to food, which lead to danger, and so on. Still, Aldis admits that it is difficult to differentiate between serious exploration and play, and that often a new and unknown environment or object is approached by serious exploration in the beginning and then gradually explored further through play.   In our opinion exploration performed in a play “atmosphere,” such as pretend play, is a kind of exploratory play, teaching the players about their environment though play situations.

Anti-phobic effect. The fear of separation from caretakers is common in humans (Buss, 2004) – particularly for the female part of the human population (Silove et al., 1995).The urge among children for going exploring on their own is puzzling in this view.

In our hominin ancestors’ past, getting lost probably was a real danger, highlighting the adaptive function  of initial separation anxiety in young children. Are these children less anxious than would have been  adaptive for them in the past? In most western societies children sleep alone, which is both culturally  and  evolutionarily a novel situation. One might speculate that this may create a larger degree of individuality and also a hypophobia of being alone. In any case, as the child matures, independence and  investigation of the surroundings is necessary – also in order to find food to feed themselves.

Is  separation  anxiety  an  evolved  non-associative  fear  that  can  benefit  from desensitization/habituating  behavior?  A  study  by  Poulton  et  al.  (2001)  revealed  that separation  anxiety was largely independent of associative factors, strongly supporting a non-associative explanation. Interestingly the results showed that the amount of separation experiences before age nine correlated negatively with the separation anxiety symptoms at age 18, suggesting an “inoculation” effect  of early  separation events. The results also indicated that planned separations can help children to learn not to fear separations. These results  support  the  assumption  of  children’s  voluntary  separation  from  caretakers,  by wandering off alone, as a mode of anti-phobic behavior. As in the case of anti-phobic effects of play in great heights (Poulton et al., 1998), one could expect that children with less fear of separation would be  more willing to expose themselves to separation events than children with a high fear of separation.  Even  so, when having the opportunity to voluntarily plan and carry out a separation from their  caretakers  by exploring new and unknown  areas,  experiencing  the  thrill  of  the  risk  of  being  lost,   children  seem  to “inoculate” themselves from the anxiety of separation.

Play with dangerous tools
Play with tools that are potentially dangerous included behaviors such as using a knife for whittling, a saw for cutting down branches, a hammer and nails for carpentering, and an axe for chopping wood (Sandseter, 2007a, 2007b). This is one of the categories that are risky from an adult point of view, while the children are more disposed to feel this is only an exciting activity (Sandseter, 2007a). It is also worth noting that this behavior was much more typical among children, and not considered risky by adults  only one or two generations ago.

Possible functions. Play with dangerous tools can be regarded as a kind of object play. The central point of object play is manipulation of objects in different ways, such as hitting  and  throwing  them  (Bjorklund  and  Pellegrini,  2002;  Pellegrini  and  Bjorklund, 2004). Pellegrini and Bjorklund (2004) argue that the large amount of time children spend in  play  and  manipulation  of  objects  is  an  indication  of  the  importance  and  adaptive relevance this has for competencies both in childhood and later in life. Also supporting the adaptive function, play with objects has been described in a wide variety of human cultures throughout the world (Gosso et al., 2005; Smith, 2005). Object play is also observed in non-human mammals and great apes (Bruner, 1976; Pellegrini and Bjorklund, 2004; Power, 2000; Ramsey and McGrew, 2005; Smith, 1982). Aldis (1975) observed object play among some kinds of carnivores and to some extent among primates, although primates tend to be more engaged in serious exploration and manipulation of objects. Still, Aldis’ results show that the serious exploration of objects often turned into play with objects when the primates were more familiar with the new object.

Play with objects is beneficial for individuals to learn properties of objects and their functions, and seems to be valuable in emergent tool use (Bjorklund and Pellegrini, 2002). The fact that boys are more likely than girls to engage in object oriented play, and they do object play more vigorously  and physically while girls seem to engage in more solitary manipulation of objects, suggests that this  provides deferred benefits of important skill acquisition for the adult human where males would have to prepare for hunting and women for gathering (Bjorklund and Pellegrini, 2002; Pellegrini and Bjorklund, 2004).

Anti-phobic effect. Some forms of hypophobia (Marks and Nesse, 1994) will be due to a mismatch  between our ancestors’ environment that we are adapted to (Nesse and Williams, 1995; Tooby and Cosmides, 1990) and the current environment. Many dangerous tools never existed in the past and we did  not evolve natural fears of them. Even though tools such as knives and axes existed in earlier phases of human evolution (although less sharp), object play (including playing with dangerous tools) more likely is motivated by an interest in tools and acquisition of tool handling skills than by anti-phobic effects. Future research into the differences between play involving modern tools and role-playing adult skill behavior might shed light into the different motivational mechanisms.

Play near dangerous elements
Play near dangerous elements in Sandseter’s (2007a, 2007b) study included play on top of high and steep cliffs, play near deep water by the seaside and tumultuous play near a burning fire pit.  Like in the case of play with dangerous tools, this is a category that primarily is regarded risky from an adult point of view, while some of the children thought this was scary and others did not (Sandseter, 2007a).

Possible functions. Similar to some of the other categories of risky play, one can assume that this kind of play serves a function of exploring the environment and becoming familiar with its possibilities and constraints. Still, research shows that some of the children are not very attentive to the fact that they are playing near a dangerous element, but rather are preoccupied in their activity, such as role play, play chasing and the like (Sandseter, 2007b). The potential hazard  is thus not  always perceived by the children (Sandseter, 2007a). The function of playing near dangerous elements may therefore be an indirect function, the dangerous element not being the essential part of the play itself, still having an effect on how children learn to handle different environmental features and elements such as water, steep and high cliffs, and fire.  Children have been playing close to dangerous ecological features throughout our species’ evolutionary  history – so one would assume that there has been selection to improve children’s ability to be aware of real risks.

Anti-phobic  effect.  If one  assumes  that  fear  of potentially  dangerous elements, similar to fear of height (Poulton et al., 1998), are non-associative evolutionarily-relevant fears that arise naturally in young humans, the hypothesis of habituation through exposure to the stimuli and the falsification of  exaggerated belief of hazards through behavioral experiments would be reasonable also for fear of high and steep cliffs, water and fire. It is possible that the children who were not afraid of dangerous elements in Sandseter’s (2007a, 2007b) studies have had more anxiety reducing experiences than the ones that thought that playing  near  dangerous  elements  was  scary.  We  addressed  the anti-phobic  effect  of experiencing injurious falls through exposing oneself to great heights above (Poulton et al., 1998). A study carried through by Poulton et al. (1999) found similar results on fear of water. This study concluded that there was no relationship between water confidence and experiencing water trauma before age nine and the symptoms of water fear at age 18. The authors conclude (see also Poulton and Menzies, 2002a; Poulton and Menzies, 2002b) that their studies support a non-associative perspective arguing that the fear of water arises due to innate reasons. Thus, anxiety is due to maturation,  rather than associative learning of anxiety (Rachman, 1977). Further, Poulton et al. (1999) conclude that  anxiety is reduced over  time  with repeated  exposure to  the stimuli.  Thus,  play  behavior  near  dangerous elements such as high cliffs, water and fire may be natural, anti-phobic behavior, while preventing this behavior may increase the risk of phobias and a lack of normal coping behavior in heights, water or close to fire.

Survival Tasks, Functions and Sex-Differences
One would assume that all children would gain from enhancing physical, social and perceptual skills and being familiar and comfortable in their surrounding environment, as well as acquiring good risk management skills and anti-phobic effects of stimulation. Still, research concludes on boys being far more represented than girls in the willingness to take risks and  engage  in risky play (Cairns and  Cairns,  1994;  Ginsburg  and  Miller,  1982; MacDonald,  1995;  Morrongiello  and  Rennie,  1998;  Smith,  1998),  intense  challenging physical play and rough-and-tumble play (Blurton Jones, 1976; DiPietro, 1981; Eaton and Enns, 1986; Eaton and Yu, 1989; Humphreys and Smith, 1984, 1987; MacDonald, 1998; Pellegrini and  Smith,  1998; Power,  2000; Smith,  1997,  2005).  Research  findings also indicate that boys have a higher injury  liability than girls (Boles, Roberts, Brown, and Mayes, 2005; Coppens and Gentry, 1991; Matheny, 1987; Morrongiello and Rennie, 1998; Ordoñana et al., 2008; Rosen and Peterson, 1990; Schwebel, Brezausek, and Belsky, 2006). Can this sex-difference be accounted for in an evolutionary perspective? Several authors (see, e.g., Bjorklund and Pellegrini, 2000, 2002; Ellis and Bjorklund, 2005; Jarvis, 2006; Pellegrini and Bjorklund, 2004; Smith, 1982) state that the documented sex-differences in play  styles  is  consistent  with  the  adaptive  problems  males  and  females  have  had  to encounter. Men have had to prove themselves  as  a strong, safe, protective and worthy partner for the females with whom he wanted to produce  offspring (Ellis, 1992). This would, in the past, imply the willingness to take great risks (Kruger and  Nesse, 2004; Wilson  and  Daly,  1985).  This  includes  both travelling  away  from the  home  base  for hunting and fighting wild animals, and protecting the partner and offspring from enemies and other  “hostile  forces of nature.” Women, on the other hand, would have to be more cautious  to  survive  and  secure  reproductive  success,  and  then  serve  as  the  primary caregivers for their children staying at the  home base performing gathering tasks. Sex- differences in the urge for risky play could possibly be viewed as an adaptation to enhance competencies important for survival in the history of evolution. Differences in fearfulness or anxiety, and the need to reduce both fear and anxiety more in males, may be part of this (Kruger and Nesse, 2004; Wilson and Daly, 1985).

General Discussion
Anxiety etiology has been based on, e.g., Mowrer’s two-factor theory – including both  classical  and  operant  conditioning  (see  also  Rachman,  1977,  for  a  conditioning approach).  This  is  no  longer  considered  a  likely  explanation.  At  least  the associative pathways might need to be expanded with non-associative models (Poulton and Menzies, 2002a).  The  isomorphic  principle  of  how  pathogenesis  and  cure  need  to  be  similar processes has  been typical within much psychotherapeutic theory – since the effective treatment of anxiety has been learning theory-based, many have expected conditioning to be the etiology of anxiety. At the same time  researchers such as Poulton and Menzies (2002a, 2002b), and Kendler, Myers and Prescott (2002)  provide strong evidence that suggests that anxiety appears through largely maturational or dispositional mechanisms. On the other hand, anxiety reduction seems to  be due to  coping  and  interaction with the naturally fear-generating stimulus. The naturally developed fear seems to be alleviated through normal habituation or coping experiences, somehow. We suggest that risky play provides the exact conditions that will be most curative of any anxiety, the exaggerated fear reactions to stimulus or situations that the child in reality is able to master. These are: the motivation to seek out the stimulus (exposure/experience) and to learn how to master the stimuli  while  being  motivated  by  a  positive  (thrilling)  rather  than  aversive  emotion resulting in coping/mastery experiences. Note that thrill reduction occurs after a period of careful  but thrill motivated negotiation of the threatening condition and the learning and mastery of the necessary skills involved. In other words, the child starts off with a natural inhibition toward situations that the child  developmentally is not mature enough to cope with, but this fear is reduced as the child develops mental and physical skills and exposes itself to the stimulus motivated by thrilling emotions, while learning how to  master these challenges.

Children do not consciously consider the immediate or deferred benefits of their play while playing or while deciding what to play. Enjoyment or thrill of play is basically the motivational basis for play among children (Smith, 1982), and children engage in risky play because they enjoy doing it (Sandseter, 2007c, 2009). Sutton-Smith (1997) states that there is no contradiction between assuming that a  child’s personal reason for play is an intrinsic motivation to experience positive emotional stages such as  arousal, excitement, fun,  merriment,  joy, ecstatic feelings,  mastery and competence, and assuming that  the effects of such play are useful for other kinds of adaptations such as enhancing survival and the child’s fitness. This corresponds to hominins procreating through history, not primarily due to the conscious desire to have offspring, but due to sexual drives and the pleasures of sex.

Still,  several  important  questions  remain  unanswered:  It  is  important  not  to prematurely conclude that risky play is due to specific adaptations or plays an adaptive role in  normal  development.  Other  explanations  are  possible:  Are  the  motivational  and perceptual mental systems that make children experience this form of stimulation activating and   thrilling   by-products   (Gould   and   Lewontin,   1979;   see   also   Buss,   Haselton, Shackelford, Bleske, and Wakefield, 1998; Kennair, 2002) of our mental mechanisms? Or might  they  be  remnants  of  systems  that,  e.g.,  made  our  tree  dwelling  ancestors  feel motivated to climb and jump from branch to branch? Would this have consequences? And is it still a system that needs stimulating in order to ensure normal development?

Few deprivation studies have been conducted to try to reveal the developmental importance of different kinds of play. This has been more common in animal play literature (Bjorklund and Pellegrini, 2002). Still, some studies of the effects of depriving children of locomotor play have occurred. The results from these studies were consistent in showing that deprivation led to increased levels of locomotor play when the opportunities for this kind of play  were  re-established (Byers and Walker, 1995; Pellegrini and Davis, 1993; Pellegrini, Huberty, and Jones, 1995). Further research would be necessary to consider the effects of preventing risky play. If this indeed resulted in an increased tendency toward fearfulness or neuroticism this would provide further evidence of the fear reducing effect of risky play.

We have been informed by a modular approach, and posited specific mechanisms for specific  types of risky play. One might object that a more domain general approach might also be possible to explain such behavior. We do believe that heights, speed and play near dangerous elements probably use many of the same mechanisms, and although there probably are different mechanisms involved in rough and tumble play, probably there also are common  processes such as the thrilling emotion. We do posit at that level that this process is rather general. Also there may be evolved individual differences (see Buss and Hawley, 2011) that regulate this process at a general level, such as poor self-regulation and inhibitory abilities that both reflect general universal development of the prefrontal cortex as well as  individual differences,  as well as  meta-cognitive processes  involved  in the overestimation of abilities to manage risky situations.

Conclusions
This article suggests that one of the most important aspects of risky play may be the anti-phobic  effect  of  exposure  to  typical  fear  eliciting  stimuli  and  contexts,  in  the combination of positive emotion and relative safety and with autonomous coping behavior. As such risky play mirrors effective  cognitive behavioral therapy of anxiety (Allen and Rapee, 2005). Current research on the etiology of anxiety suggests that anxieties develop due to both genetic and environmental factors (Allen and Rapee, 2005). The specific genes have not been identified, but neither are we aware of what environmental  factors cause anxiety  disorders  (e.g.  Kendler  et  al.,  2002).  It  seems  that  the  genetic  factors  cause individual differences, and apart from the phobias most anxiety disorders do not seem functional from  an  evolutionary perspective (Kennair, 2007). The evidence that phobias seem to develop rather  independently of learning experiences (these have at least been difficult to document to date), does not mean that learning may not be a way of reducing or even curing anxiety. Actually graded exposure and learning to think less negative and more mastery oriented thoughts about the anxiety producing stimuli have shown to be the most effective treatment of child anxieties (Allen and Rapee, 2005). It is possible that risky play is a natural way of reducing many phobic reactions that are functional when the child has a low level of  mastery of the fear provoking conditions. Thus adaptive fear, necessary to keep the child safe and alert and careful when learning to cope with potentially dangerous situations for young children, is countered by the positive emotions that are typical of the adaptively thrilling experience involved in moving the boundaries of what is safe and what is dangerous. Research has shown that anxious children may elicit overprotective behavior from others, such as parents and caretakers, and that this reinforces the child’s perception of threat and decreases their perception of controlling the danger (Allen and Rapee, 2005). Overprotection might thus result in exaggerated levels of anxiety. Overprotection through governmental control of playgrounds and exaggerated fear of playground accidents might thus result in an increase of anxiety in society. We might need to provide more stimulating environments for children, rather than hamper their development.

This  means  that  some  forms  of  risky  play  may  be  developmentally  adequate species-specific and universal anti-phobic processes. For other types of risky play, the motivational systems may be more archaic systems or they may be due to by-products of our  perceptual  systems  that  provide  a  mixed  activation  that  the  children  perceive  as thrilling and hedonic. The different analyses of function give different testable hypotheses of the psychological mechanisms and motivational systems involved in the different types of play. From a modular approach one would not expect to find the same  mechanisms involved in all different types of behavior.

If these ideas are correct, this might not only be about prevention or increasing anxiety at the population level, but also relevant for the improvement of treatment of young children with anxiety. Treatment might profit from having more than merely a habituation perspective; relaxation (e.g., Öst, 1987) may counter anxiety, but it may be more important – at least for many young patients – to experience more thrilling and coping emotions. A treatment  program for  young  patients that  uses thrilling  emotions to  cure anxiety and compares it to current best practice cognitive behavioral treatment protocols would test this directly.

Further research into risky play is necessary. Risky behavior is a potential health hazard. At the same time, an understanding of why and when children will engage in risky behavior is  important – not least if such behavior in the long run is beneficial to their normal development. It seems that risky behavior is maintained despite adults’ attempts at making children’s environments safer. From  both a safety perspective as well as from a normal psychological developmental perspective an understanding of the function of risky play and the different psychological mechanisms and motivational  systems involved are important to understand. This will be essential in the world wide discussion on demands for children’s play safety,  by a growing  number  of researchers regarded  as drawing  near overprotection, and the balance between such safety requirements and children’s needs for opportunities to play freely in challenging, stimulating and developing environments. Even though highly active and risk taking children experience more (albeit minor) injuries, this article suggests that these children will benefit psychologically from natural adaptive fear alleviation and the anti-phobic effect of risky play.

Acknowledgements: Thanks to Bruce Ellis and his group for comments on an earlier version of this  article.  We also  thank the anonymous reviewers for  many helpful and insightful suggestions that improved the arguments and discussion of this article.

Received 28 December 2010; Revision submitted 1 June 2011; Accepted 8 June 2011

References

• Adams, J. (2001). Risk. London: Routledge.
• Aldis, O. (1975). Play fighting. New York: Academic Press.
• Allen, J. L., and Rapee, R. M. (2005). Anxiety disorders. In P. J. Graham (Ed.), Cognitive behaviour  therapy for children and families (2nd ed., pp. 300-319). Cambridge: Cambridge University Press.
• Apter, M. J. (2007). Danger: Our quest for excitement. Oxford: Oneworld.
• Ball, D. J. (1995). Applying risk management concepts to playground safety. In M. L.
• Christiansen  (Ed.),  Proceedings  of  the  international  conference  of  playground safety (pp. 21-26). Pennsylvania: Penn State University: Center  for Hospitality, Tourism and Recreation Research.
• Ball, D. J. (2002). Playgrounds – Risks, benefits and choices (Vol. 426/2002). London: Health and Safety Executive (HSE) contract research report, Middlesex University.
• Ball,  D.  J.  (2004).  Policy  issues  and  risk-benefit  trade-offs  of  ”safer  surfacing”  for children’s playgrounds. Accident Analysis and Prevention, 36, 661-670.
• Ball, D., Gill, T., and Spiegal, B. (2008). Managing risk in play provision: Implementation guide. Nottingham: DCSF Publications.
• Barkley,   R.   A.   (2001).   Accidents   and   attention-deficit/hyperactivity  disorder.   The Economics of Neuroscience, 3, 64-68.
• Bekoff, M., and Byers, J. A. (1981). A critical reanalysis of the ontogeny and phylogeny of mammalian   social   and  locomotor  play:  An  ethological  hornet’s  nest.  In  K. Immelmann, G. W. Barlow,  L. Petrinovich, and M. B. Main (Eds.), Behavioral development:  The  Bielefeld  interdisciplinary  project  (pp.  296-337).  Cambridge: Cambridge University Press.
• Bienefeld,  M.,  Pickett,  W.,  and  Carr,  P.  A.  (1996).  A descriptive study of childhood injuries in Kingston, Ontario, using data from a computerized injury surveillance system. Health Canada – Chronic Diseases in Canada, 17, 21-27.
• Bjorklund, D. F. (1987). A note on neonatal imitation. Developmental Review, 7, 86-92. Bjorklund, D. F., and Ellis, B. J. (2005). Evolutionary psychology and child development: An emerging synthesis. In B. J. Ellis and D. F. Bjorklund (Eds.), Origins of the social mind. Evolutionary psychology and child development (pp. 3-18). New York, USA: Guilford.
• Bjorklund,  D.  F.,  and  Pellegrini,  A.  D.  (2000).  Child  development  and  evolutionary psychology. Child Development, 71, 1687-1708.
• Bjorklund, D. F., and Pellegrini, A. D. (2002). The origins of human nature: Evolutionary developmental psychology.  Washington, D.C.:  American Psychological Association.
• Blasi, C. H., and Bjorklund, D. F. (2003). Evolutionary developmental psychology: A new tool for better understanding human ontogeny. Human Development, 46, 259-281. Blurton Jones, N. (1976). Rough-and-tumble play among nursery school children. In J. S. Bruner, A. Jolly, and K. Sylva (Eds.), Play: It’s role in development and evolution (pp. 352-363). Harmondsworth: Penguin Books.
• Boles, R. E., Roberts, M. C., Brown, K. J., and Mayes, S. (2005). Children’s risk taking behaviors: The role of child-based perceptions of vulnerability and temperament. Journal of Pediatric Psychology, 30, 562-570.
• Boulton, M. J., and Smith, P. K. (1994). Bully/victim problems in middle-school children: Stability, self-perceived competence, peer perceptions and peer acceptance. British Journal of Development Psychology, 12, 315-329.
• Boulton, M. J., and Smith, P. K. (1996). Liking and peer perceptions among Asian and white British children. Journal of Social and Personal Relationships, 13, 163-177. Boyer,  T.  W.   (2006).  The  development  of  risk-taking:  A  multi-perspective  review. Developmental Review, 26, 291-345.
• Broidy, L. M., Nagin, D. S., Tremblay, R. E., Bates, J. E., Brame, B., Dodge, K. A., … Vitaro, F. (2003). Developmental trajectories of childhood disruptive behaviors and adolescent delinquency: A six-site, cross-national study. Developmental Psychology, 39, 222-245.
• Bruner, J. S. (1976). Nature and uses of immaturity. In J. S. Bruner, A. Jolly, and K. Sylva (Eds.), Play: It’s role in development and evolution (pp. 28-63). Harmondsworth: Penguin Books.
• Buss,  A.  H.  (1997).  Evolutionary  perspectives  on  personality  traits.  In  R.  Hogan,  J. Johnson, and S. Briggs (Eds.), Handbook of personality psychology (pp. 346-366). San Diego, CA: Academic Press.
• Buss, D. M. (2004). Evolutionary psychology: The new science of the mind (2nd ed.). Boston, MA: Pearson.
• Buss, D. M., Haselton, M. G., Shackelford, T. K., Bleske, A., and Wakefield, J. C. (1998). Adaptations, exaptations, and spandrels. American Psychologist, 53, 533-548.
• Buss, D.M., and Hawley, P. H. (Eds.) (2011). The evolution of personality and individual differences. New York: Oxford University Press.
• Byers,  J.  A.,  and  Walker,  C.  (1995).  Refining  the  motor  training  hypothesis  for  the evolution of play. The American Naturalist, 146, 25-40.
• Cairns, R. B., and Cairns, B. D. (1994). Lifelines and risks: Pathways of youth in our time. New York: Cambridge University Press.
• Cataldo, M. F., Finney, J. W., Richman, G. S., and Riley, A. W. (1992). Behavior of injured and uninjured children and their caregivers in a simulated hazardous setting. Journal of Pediatric Psychology, 17, 73-80.
• Chalmers, D. (2003). Playground equipment safety standards. Safe Kids News, 21, 4. Chalmers, D. J., Marshall, S. W., Langley, J. D., Evans, M. J., Brunton, C. R., Kelly, A. M., and Pickering, A. F. (1996). Height and surfacing as risk factors for injury in falls from playground equipment: A case-control study. Injury Prevention, 2, 98- 104.
• Coppens,  N.  M.,  and  Gentry,  L.  K.  (1991).  Video  analysis  of playground  injury-risk situations. Research in Nursing and Health, 14, 129-136.
• Cosmides, L., and Tooby, J. (1987). From evolution to behavior: Evolutionary psychology as the missing link. In J. Dupré (Ed.), The latest on the best: Essays on evolution and optimality (pp. 276-306). Cambridge, MA: The MIT Press. Children’s risky play from an evolutionary perspective
• Cosmides, L., and Tooby, J. (1994). Beyond intuition and instinct blindness: The case for an evolutionarily rigorous cognitive science. Cognition, 50, 41-77.
• Dal  Santo,  J.  A.,  Goodman,  R.  M.,  Glik,  D.,  and  Jackson,  K.  (2004).  Childhood unintentional injuries: Factors predicting injury risk among preschoolers. Journal of Pediatric Psychology, 29, 273-283.
• Davidsson, B. (2006). The schoolyard as a place of meaning: Children’s perspectives. In J. Brodin and P. Lindstrand (Eds.), Interaction in outdoor play environments: Gender, culture  and   learning  (Vol.  Research  Report  no.  47,  pp.  61-79).  Stockholm: Stockholm Institute of Education.
• DiLillo,  D.,  Potts,  R.,  and  Himes,  S.  (1998).  Predictors  of children’s  risk  appraisals. Journal of Applied Developmental Psychology, 19, 415-427.
• DiPietro,  J.  A.  (1981).  Rough-and-tumble  play:  A  function  of gender.  Developmental Psychology, 17, 50-58.
• DiScala, C., Lescohier, I., Barthel, M., and Li, G. (1998). Injuries to children with attention deficit hyperactivity disorder. Pediatrics, 102, 1415-1421.
• Dodge, K. A., Coie, J. D., Pettit, G. S., and Price, J. M. (1990). Peer status and aggression in boys’ groups: Developmental and contextual analyses. Child Development, 61, 1289-1309.
• Eaton, W. O., and Enns, L. R. (1986). Sex differences in human motor activity level.
• Psychological Bulletin, 100, 19-28.
• Eaton, W. O., and Yu, A. P. (1989). Are sex differences in child motor activity level a function of differences in maturational status? Child Development, 60, 1005-1011.
• Ellis, B. J. (1992). The evolution of sexual attraction: Evaluative mechanisms in women. In
• J. H. Barkow, L. Cosmides, and J. Tooby (Eds.), The adapted mind: Evolutionary psychology  and  the  generation  of  culture  (pp.  267-288).  New  York:  Oxford University Press.
• Ellis,  B.  J.,  and  Bjorklund,  D.  F.  (2005).  Origins  of  the  social  mind:  Evolutionary psychology and child development. New York: Guilford Press.
• Flinn, M. V., and Ward, C. V. (2005). Ontogeny and evolution of the social child. In B. J. Ellis  and  D.  F.  Bjorklund  (Eds.),  Origins  of  the  social  mind:  Evolutionary psychology and child development (pp. 19-44). New York: Guilford Press.
• Freeman, C. (1995). The changing nature of children’s environmental experience: The shrinking realm of outdoor play. International Journal of Environmental Education and Information, 14, 259-280.
• Fry, D. P. (2005). Rough-and-tumble social play in humans. In A. D. Pellegrini and P. K. Smith (Eds.), The nature of play: Great apes and humans (pp. 54-85). New York: The Guilford Press.
• Gayton, W. F., Bailey, C., Wagner, A., and Hardesty, V. A. (1986). Relationship between childhood hyperactivity and accident proneness. Perceptual and Motor Skills, 63, 801-802.
• Ginsburg,  H.  J.,  and  Miller,  S.  M.  (1982).  Sex  differences  in  children’s  risk-taking behavior. Child Development, 53, 426-428.
• Gleser, J. M., and Lison, S. (1992). Judo as therapy for emotionally disturbed adolescents: A pilot study. Perceptual and Motor Skills, 74, 915-925.
• Gosso, Y., Otta, E., de Lima Salum e Morais, M., Ribeiro, F. J. L., and Bussab, V. S. R. (2005). Play in hunter-gatherer society. In A. D. Pellegrini and P. K. Smith (Eds.), The nature of play: Great apes and humans (pp. 213-253). New York: The Guilford Press.
• Gould, S. J., and Lewontin, R. C. (1979). The spandrels of San Marco and the Panglossian paradigm: A  critique of the adaptationist programme. Proceedings of the Royal Society of London B, 205, 581-598.
• Greenfield, C. (2003). Outdoor play: The case of risks and challenges in children’s learning and development. Safekids News, 21, 5.
• Heseltine, P. (1995). Safety versus play value. In M. L. Christiansen (Ed.), Proceedings of the International Conference of Playground Safety (pp. 91-95). University Park, PA: Penn   State   University:  Center  for  Hospitality,  Tourism  and  Recreation Research.
• Hillier, L. M., and Morrongiello, B. A. (1998). Age and gender differences in school-age children’s appraisals of injury risk. Journal of Pediatric Psychology, 23, 229-238. Humphreys,  A.   P.,   and  Smith,  P.  K.  (1984).  Rough-and-tumble  in  preschool  and playground. In P.  K. Smith (Ed.), Play in animals and humans (pp. 241-266). Oxford: Blackwell.
• Humphreys, A. P., and Smith, P. K. (1987). Rough and tumble, friendship, and dominance in  schoolchildren: Evidence for continuity and change with age. Child Development, 58, 201-212.
• Illingworth, C., Brennan, P., Jay, A., Al-Ravi, F., and Collick, M. (1975). 200 injuries caused by playground equipment. British Medical Journal, 4, 332-334.
• Jaquess, D. L., and Finney, J. W. (1994). Previous injuries and behavior problems predict children’s injuries. Journal of Pediatric Psychology, 19, 79-89.
• Jarvis, P. (2006). Rough and tumble play: Lessons in life. Evolutionary Psychology, 4, 330- 346.
• Jokela, M., Power, C., and Kivimaki, M. (2009). Childhood problem behaviors and injury risk over the life course. Journal of Child Psychology and Psychiatry, 50, 1541- 1549.
• Kaarby, K. M. E. (2004). Children playing in nature. Paper presented at the CECDE conference: Questions of quality, Dublin Castle.
• Kendler,  K.  S.,  Myers,  J.,  and  Prescott,  C.  A.  (2002).  The  etiology  of  phobias:  An evaluation of the stress-diathesis model. Archives of General Psychiatry, 59, 242- 248.
• Kennair, L. E. O. (2002). Evolutionary psychology: An emerging integrative perspective within the science and practice of psychology. Human Nature Review, 2, 17-61. Kennair, L. E. O. (2003). Evolutionary psychology and psychopathology. Current Opinion in Psychiatry, 16, 691-699.
• Kennair, L. E. O. (2007). Fear and fitness revisited. Journal of Evolutionary Psychology, 5, 105-117.
• Kennair, L. E. O. (2011). The problem of defining psychopathology and challenges to evolutionary psychology theory.  In D.  M.  Buss  and  P.  H.  Hawley (Eds.), The evolution of  personality  and  individual  differences  (pp.  451-479).  New  York: Oxford University Press.
• Kruger, D. J., and Nesse, R. M. (2004). Sexual selection and the male:female mortality ratio. Evolutionary Psychology, 2, 66-77.
• Lamarre, B. W., and Nosanchuk, T. A. (1999). Judo – the gentle way: A replication of studies on martial arts and aggression. Perceptual and Motor Skills, 88, 992-996. Little, H. (2006). Children’s risk-taking behaviour: Implications for early childhood policy and practice. International Journal of Early years Education, 14, 141-154.
• Little, H. (2010). Young children’s physical risk-taking behaviour during outdoor play: The influence of individual, social and environmental factors.  Doctoral thesis, Macquarie University, Sydney.
• Lupton, D., and Tulloch, J. (2002). ‘Life would be pretty dull without risk’: Voluntary risk taking and its pleasures. Health, Risk and Society, 4, 113-124.
• MacDonald, K. (1995). Evolution, the five-factor model, and levels of personality. Journal of Personality, 63, 525-567.
• MacDonald, K. (1998). Evolution, culture, and the five-factor model. Journal of Cross- Cultural Psychology, 29, 119-149.
• Mack, M. G., Hudson, S., and Thompson, D. (1997). A descriptive analysis of children’s playground injuries in the United States 1990-4. Injury Prevention, 3, 100-103.
• Marks, I. M., and Nesse, R. M. (1994). Fear and fitness: An evolutionary analysis of anxiety disorders. Ethology and Sociobiology, 15, 247-261.
• Matheny, A. P. J. (1987). Psychological characteristics of childhood accidents. Journal of Social Issues, 43, 45-60.
• Miller, D. C., and Byrnes, J. P. (1997). The role of contextual and personal factors in children’s risk taking. Developmental Psychology, 33, 814-823.
• Morrongiello, B. A., and Rennie, H. (1998). Why do boys engage in more risk taking than girls? The role of attributions,  beliefs, and risk  appraisals Journal of  Pediatric Psychology, 23, 33-43.
• Morrongiello, B. A., and Lasenby-Lessard, J. (2006). Finding the daredevils: Development of a  sensation-seeking scale for children that is relevant to physical risk-taking. Accident Analysis and Prevention, 38, 1101-1106.
• Morrongiello, B. A., and Matheis, S. (2004). Determinants of children’s risk-taking in different  social  situational  contexts:  The  role  of  cognitions  and  emotions  in predicting children’s decisions. Journal of Applied Developmental Psychology, 25, 303-326.
• Morrongiello,  B.  A.,  and  Matheis,  S.  (2007).  Understanding  children’s  injury-risk behaviors: The independent contributions of cognitions and emotions. Journal of Pediatric Psychology, 32, 926-937.
• Morrongiello, B. A., Ondejko, L., and Littlejohn, A. (2004). Understanding toddlers’ in- home  injuries:  I.   Context,  correlates,  and  determinants.  Journal  of  Pediatric Psychology, 29, 415-431.
• Morrongiello, B. A., and Sedore, L. (2005). The influence of child attributes and social- situational context on school-age children’s risk-taking behaviors that can lead to injury. Journal of Applied Developmental Psychology, 26, 347-361.
• Nesse, R. M., and Williams, G. C. (1995). Evolution and healing: The new science of  Darwinian medicine. London: Weidenfeld and Nicholson.
• Ordoñana, J. R., Caspi, A., and Moffitt, T. E. (2008). Unintentional injuries in a twin study of preschool children: Environmental, not genetic, risk factors. Journal of Pediatric Psychology, 33, 185-194.
• Öst, L. G. (1987). Applied relaxation: Description of a coping technique and review of controlled studies. Behaviour Research and Therapy, 25, 397-409.
• Pellegrini, A. D., and Bjorklund, D., F. (2004). The ontogeny and phylogeny of children’s object and fantasy play. Human Nature, 15, 23-43.
• Pellegrini, A. D., and Davis, P. (1993). Confinement effects on playground and classroom behavior. British Journal of Educational Psychology, 63, 88-95.
• Pellegrini, A. D., Dupuis, D., and Smith, P. K. (2007). Play in evolution and development. Developmental Review, 27, 261–276.
• Pellegrini, A. D., Huberty, P. D., and Jones, I. (1995). The effects of play deprivation on children’s   recess   and   classroom  behaviors.   American  Educational  Research Journal, 32, 845-864.
• Pellegrini, A. D., and Long, J. D. (2003). A sexual selection theory longitudinal analysis of sexual segregation and integration in early adolescence. Journal of Experimental Child Psychology, 85, 257–278.
• Pellegrini, A. D., and Smith, P. K. (1998). Physical activity play: The nature and function of a neglected aspect of play. Child Development, 69, 577-598.
• Peterson, L., Gillies, R., Cook, S., Schick, B., and Little, T. (1994). Developmental patterns of expected consequences for simulated bicycle injury events. Health Psychology, 13, 218-223.
• Phelan, K., Khoury, J., Kalkwarf, H., and Lamphear, B. (2001). Trends and patterns of playground injuries in United States. Ambulatory Pediatrics, 1, 227-233.
• Pinker, S. (1995). The language instinct: The new science of language and mind. London: Penguin Books.
• Pinker, S. (1997). How the mind works. Harmondsworth, UK: The Penguin Press.
• Plumert,  J.  M.  (1995).  Relations  between  children’s  overestimation  of  their  physical abilities and accident proneness. Developmental Psychology, 31, 866-875.
• Plumert,  J. M.,  and  Schwebel,  D.  C.  (1997). Social and  temperamental influences on children’s overestimation of their physical abilities: Links to accidental proneness. Journal of Experimental Child Psychology, 67, 317-337.
• Potts, R. P., Martinez, I. G., and Dedmon, A. (1995). Childhood risk-taking and injury: Self-report and informant measures. Journal of Pediatric Psychology, 20, 5-12. Poulton, R., and  Menzies, R. G. (2002a). Fears born and bred: Toward a more inclusive theory of fear acquisition. Behaviour Research and Therapy, 40, 197-208.
• Poulton, R., and Menzies, R. G. (2002b). Non-associative fear acquisition: A review of the evidence from retrospective and  longitudinal research. Behaviour Research and Therapy, 40, 127-149.
• Poulton, R., Davies, S., Menzies, R. G., Langley, J. D., and Silva, P. A. (1998). Evidence for  a  non-associative  model of the acquisition  of a  fear  of heights.  Behaviour Research and Therapy, 36, 537-544.
• Poulton, R., Menzies, R. G., Craske, M. G., Langley, J. D., and Silva, P. A. (1999). Water trauma and swimming experiences up to age 9 and fear of water at age 18: A longitudinal study. Behaviour Research and Therapy, 37, 39-48.
• Poulton, R., Milne, B. J., Craske, M. G., and Menzies, R. G. (2001). A longitudinal study of the etiology of separation anxiety. Behaviour Research and Therapy, 39, 1395- 1410.
• Poulton,  R.,  Waldie,  K.  E.,  Craske,  M.  G.,  Menzies,  R.  G.,  and  McGee,  R.  (2000). Dishabituation processes in height fear and dental fear: An indirect test of the non- associative  model of fear acquisition. Behaviour Research and Therapy, 38, 909- 919.
• Poulton, R., Waldie, K. E., Menzies, R. G., Craske, M. G., and Silva, P. A. (2001). Failure to overcome ‘innate’ fear: A developmental test of the non-associative model of fear acquisition. Behaviour Research and Therapy, 39, 29-43.
• Power,  T.  G.  (2000).  Play  and  exploration  in  children  and  animals.  Mahwah,  NJ: Lawrence Erlbaum.
• Rachman, S. (1977). The conditioning theory of fear-acquisition: A critical examination. Behaviour Research and Therapy, 15, 375-387.
• Rakison, D. H. (2005). Infant perception and cognition: An evolutionary perspective on early learning. In B. J. Ellis and D. F. Bjorklund (Eds.), Origins of the social mind: Evolutionary psychology and child development (pp. 317-353). New York: Guilford Press.
• Ramsey, J. K., and McGrew, W. C. (2005). Object play in great apes. In A. D. Pellegrini and P. K. Smith (Eds.), The nature of play: Great apes and humans (pp. 89-112). New York: Guilford Press.
• Rosen,  B.  N.,  and  Peterson,  L.  (1990).  Gender  differences  in  children’s outdoor  play injuries: A review and an integration. Clinical Psychology Review, 10, 187-205. Sandseter, E. B. H. (2007a). Categorizing risky play: How can we identify risk-taking in children’s play? European Early Childhood Education Research Journal, 15, 237-252.
• Sandseter,  E.  B.  H.  (2007b).  Risky  play  among  four-  and  five-year-old  children  in preschool. In S. O’Brien, P. Cassidy, and H. Shonfeld (Eds.), Vision into practice: Making  quality a reality in the  lives of  young children  (pp.  248-256). Dublin: CECDE.
• Sandseter, E. B. H. (2007c, 8.-10. February). Risky play among four- and five year old children  in  preschool.  Paper  presented  at the  meeting  of Vision  into  Practice: Making Quality a Reality in the Lives of Young Children. Dublin Castle.
• Sandseter, E. B. H. (2009). Children’s expressions of exhilaration and fear in risky play. Contemporary Issues in Early Childhood, 10, 92-106.
• Sandseter, E. B. H. (2010). Scaryfunny. A qualitative study of risky play among preschool children.  Doctoral  Thesis,  Norwegian  University  of  Science  and  Technology, Trondheim, Norway.
• Satomi,  T.  S.,  and  Morris,  V.  G.  (1996).  Outdoor  play  in  early  childhood  education settings. Is it safe and healthy for children? Early Childhood Education Journal, 23, 153-157.
• Sawyers, J. K. (1994). The preschool playground: Developing skills through outdoor play. Journal of Physical Education, Recreation and Dance, 65, 31-33.
• Scholte, R. H. J., Engels, R. C. M. E., Overbeek, G., Kemp, R. A. T., and Haselager, G. J. T. (2007). Stability in bullying and victimization and its association with social adjustment in childhood and adolescence. Journal of Abnormal Child Psychology, 35, 217-228.
• Schwebel,  D.  C.,  and  Brezausek,  C.  M.  (2004).  The  role  of  fathers  in  toddlers’ unintentional injury risk. Journal of Pediatric Psychology, 29, 19-29.
• Schwebel, D. C., and Plumert, J. M. (1999). Longitudinal and concurrent relations among temperament, ability estimation, and injury proneness. Child Development, 70, 700-712.
• Schwebel, D. C., Brezausek, C. M., and Belsky, J. (2006). Does time spent in child care influence risk  for  unintentional injury? Journal of Pediatric Psychology, 31, 184-193.
• Silove, D., Manicavasagar, V., O’Connell, D., and Morris-Yates, A. (1995). Genetic factors in early separation anxiety: Implications for the genesis of adult anxiety disorders. Acta Psychiatrica Scandinavia, 92, 17-24.
• Smith, P. K. (1982). Does play matter? Functional and evolutionary aspects of animal and human play. Behavioral and Brain Sciences, 5, 139-184.
• Smith, P. K. (1997). Play fighting and real fighting: Perspectives on their relationship. In
• A. Schmitt, K. Atswanger, K. Grammar, and K. Schafer (Eds.), New aspects of ethology (pp. 47 – 64). New York: Plenum Press.
• Smith, P. K. (2005). Play: Types and functions in human development. In B. J. Ellis and D.
• F. Bjorklund (Eds.), Origins of the social mind: Evolutionary psychology and child development (pp. 271-291). New York: Guilford.
• Smith, S. J. (1998). Risk and our pedagogical relation to children: On playground and beyond. New York: State University of New York Press.
• Spinks, A. B., Nagle, C., Macpherson, A., K., Bain, C., and McClure, R. J. (2008). Host factors  and  childhood  injury:  The  infleunce  of  hyperactivity  and  aggression. Journal of Developmental and Behavioral Pedriatrics, 29, 117-123.
• Stephenson, A. (2003). Physical risk-taking: Dangerous or endangered? Early Years, 23, 35-43.
• Stutz, E. (1995). Rethinking concepts of safety and the playground: The playground as a place in which children may learn skills for life and managing hazards. In M. L. Christiansen  (Ed.),  Proceedings  of  the  international  conference  of  playground safety. University Park, PA: Penn State University: Center for Hospitality, Tourism and Recreation Research.
• Sutton-Smith,  B.  (1997).  The ambiguity of  play.  Cambridge,  MA:  Harvard  University Press.
• Swartz, M. K. (1992). Playground safety. Journal of Pediatric Health Care, 6, 161-162. Swensen, A. R., Birnbaum, H. G., Ben Hamadi, R., Greenberg, P., Cremieux, P. Y., and
• Secnik,    K.    (2004).    Incidence    and    costs    of    accidents    among    attention- deficit/hyperactivity disorder patients. Journal of Adolescent Health, 35, e1-e9.
• Thompson,  N.  S.,  Dessureau,  B.,  and  Olson,  C.  (1998).  Infant  cries  as  evolutionary melodrama: Extortion or deception? Evolution of Communication, 2, 25-43.
• Thompson, N. S., Olson, C., and Dessureau, B. (1996). Babies’ cries: Who’s listening? Who’s being fooled? Social Research, 63, 763-784.
• Tooby, J., and Cosmides, L. (1990). The past explains the present: Emotional adaptations and the structure of ancestral environments. Ethology and Sociobiology, 11, 375-424.
• van Aken, C., Junger, M., Verhoeven, M., van Aken, M. A. G., and Deković, M. (2006). Externalizing behaviors and minor unintentional injuries in toddlers: Common risk factors? Journal of Pediatric Psychology, 32, 230-244.
• Wazana, A. (1997). Are there injury-prone children? A critical review of the literature. Canadian Journal of Psychiatry, 42, 602-610.
• Wells, A. (1997). Cognitive therapy of anxiety disorders. Chichester, UK: Wiley.
• Wilson, M., and Daly, M. (1985). Competitiveness, risk taking, and violence: The young male syndrome. Ethology and sociobiology, 6, 59-73.
• Wyver, S., Tranter, P., Naughton, G., Little, H., Sandseter, E. B. H., and Bundy, A. (2010). Ten ways to restrict children’s freedom to olay: The problem of surplus safety. Contemporary Issues in Early Childhood, 11, 263-277.