Adaptive Value

Adaptive value is the most researched area of animal play.  Because of the costs and predominance of animal play, it is likely that there is a significant adaptiveness to play.  Many of the pervasive theories about the function of play include development of physical skills, social skills, cognitive benefits, and energy regulation.  Proving any one of these theories has been difficult, as there is often support in one species and not in another.  Instead of having any single function, it is likely that animal play has multiple overlapping functions.  Additionally the benefits of play may differ from species to species, leading to support of hypothesis in some species and not others.  Because play behaviors in themselves are so diverse, the benefits of play are also likely to be diverse.


Motor Training Hypothesis:

An early hypothesis of animal play suggested that play benefits animals endurance and strength.  It is unlikely, however, that play produces any significant increases in strength or endurance do to the short durations of play. Byers and Walker (1995) suggest that play may benefit motor skills because play occurs during a critical period of development of a brain center critical for the control of motor function, the cerebellum.  Byers and Walker compared the peak of play and compared it to synapse formation and elimination in the cerebellum and found some overlap. They found that play overlapped with the terminal phases of cerebellar synapse formation and elimination.  Because experience affects cerebellar formation, the overlap of these functions may suggest that play modifies the development of the cerebellum.  Further research however has not been completed on this topic.  Below are 2 figures showing the overlap between cerebellar synaptogenesis and play in rats and mice.  This figure can be found in Byers and Walker (1995) in REFERENCES.


fig1.synaptogenesis fig2

 

Practice for adult behaviors:

Another theory suggests that animal play is adaptive as it allows young animals to practice later adult behaviors.  There is mixed support for this hypothesis, as animals deprived of play tend to develop normal adult behaviors.  For example, it is hypothesized that object play in cats represents practice for predatory behaviors.  Caro (1980) however, found that cats deprived of object play were still able to hunt effectively as adults.  Despite this result, one can support the practice hypothesis by explaining that even if play does help later adult behaviors, such important behaviors like hunting likely have compensatory mechanisms to learn this skill.  Additionally, while long-term benefits have rarely been found, the benefits of play may be short term.  Caro (1995) observed cheetah cubs and found associations between play and success in early hunting effects.  Stalking and crouching behaviors during play were associated with the same behavior during early attempts to hunt.  Additionally, contact social play was associated with contacting injured live prey released by their mother.  Cubs that covered long distances in chases during playing also tended to chase prey for longer distances, and had more success in contacting live prey.  These results suggest that play may provide early benefits for the development of adult behaviors, and give some animals a head start on these behaviors.  


Cheetah mom with prey huntingcheetahs
Figure 3. Cheetah cubs practicing hunting. Photos by Sam Stogdale. SOURCE. Figure 4. See Fig 3. for explanation and link.

 

Practice for unexpected events:

An alternative theory is that play provides practice for animals to respond to unexpected events where they experience a loss of control.  Spinka et al. (2001) presented this theory and suggested that play provides practice for these events both emotionally and cognitively.  They explain that through the self handicapping and shifting of control that is often observed during play fighting, play allows each animal to experience and react emotionally and cognitively to these events.  While this theory may provide part of the answer as to the function of play, it fails to completely explain the function of play; this theory suggests that play should occur in highly variable and possible dangerous environments, but the opposite phenomena is usually observed (for discussion see Graham & Burghardt, 2010).  Additionally, this theory fails to explain why play stops during adulthood.  Despite the issues with this theory, it may explain some part of the benefits of play.


Social Benefits:

monkeyscuddling
Figure 5. Two baby Japanese Macaques embrasing. Picture by Kiyoshi Ookawa. SOURCE.

 

Social play has often been theorized to have social benefits.  Studying the effect of social play has been difficult because of the difficulty of depriving animals of social play without depriving them of other normal social environments.  Research does however suggest that specifically social play effects later adult social skills.  Social isolation has been demonstrated to have a critical period in rats; isolation at some ages causes disruption of later social behavior, while isolation at other ages does not.  Van den Berg et al. (1999) found that the period where isolation causes disruption (weeks 4 and 5 of age) corresponds to the period of time is most frequent.  While this study isolated the rats from all social interactions, not just playing, the fact that this stage corresponds to a peak in playing behavior suggests that play fighting is important in this critical social period.  Additionally, Pellis and Pellis (2007) have attempted to prevent social play without disrupting social interaction by separating mice with a mesh divider.  These rats produced cognitive and social deficits in adult life.  Another method to provide social contact without social play, pairing juvenile rats with adult rats, resulted in the same cognitive and social deficits.  While there is significant evidence suggesting that for rats, social play provides later adult social benefits, this result has not been found in all animals (for discussion, see Graham & Burghardt, 2010).  Social play likely improves social skills in many animals, but not necessarily in all animals.  Additionally, some animals may demonstrate social benefits on a smaller scale than others.