#4. The Greatest Play Theorist You Probably Never Heard of--Karl Groos

In the late 19th century, Groos developed the first theory of play informed by an understanding of evolution by natural selection. The practice theory.

This whole series of letters is about the value of play as viewed from an evolutionary perspective. In my last letter (#3) I outlined three major categories of evolutionary functions of play. I suggested that our drive to play came about through natural selection because (1) it is a vehicle for practice of essential life skills, especially in the young; (2) it is an engine of innovation and invention, allowing us to adapt to environmental change and occupy a wide variety of niches; and (3) it promotes cooperation and allows us to live relatively peacefully as social beings. I suggested there that the first of these functions was the primary, original reason for the emergence of play among our mammalian ancestors. The person who first developed what is now called the practice theory of play was Karl Groos.

Groos was a scholar ahead of his time. Well before a scientific consensus had been reached on Darwin’s theory of evolution, Groos applied that theory in a remarkably insightful analysis of play, in two books--published originally in German as Die Spiele der Tiere (1896) and Die Spiele der Menschen (1899) and subsequently in English as The Play of Animals (1898) and The Play of Man (1901).

Groos was a professor of philosophy at the University of Basal. An initial interest in aesthetics led him to an interest in play, which, in turn, led him to ask why do animals and humans play?  He realized, as few others at his time did, that why questions of this sort are questions about natural selection. Groos had read Darwin’s writings carefully, kept up with the critiques and revisions of Darwin, and had, by today’s standards, a remarkably modern understanding of natural selection, heredity, and the ways that heredity and experience interact in the development of individuals.  He was also quite familiar with research by naturalists on the behavior of animals in the wild and by psychologists on human behavior. Among other things, he knew that the young of most if not all mammals play. Play is a universal mammalian category of behavior.

Why would natural selection lead animals to engage in the seemingly senseless sorts of activity we call play? In Groos’s time, as now, many people defined play, in part, as activity that serves no useful purpose. Not only that, but, Groos realized, play has costs. It uses energy; it is sometimes noisy and attracts predators; and some common forms of play, such as swinging around high up in trees, are downright dangerous. It would be safer, and less wasteful of energy, to spend free time tucked quietly away in a burrow or cave than to spend it in raucous play.

So, from an evolutionary perspective, play is either an accident—a side effect of evolution that natural selection couldn’t weed out—or it does, after all, serve adaptive functions that outweigh the costs. Groos was the first person to think deeply and systematically about play from this point of view, and for eighty years he also appears to have been the last person to do so. Indeed, prior to Robert Fagan’s Animal Play Behavior (1981), Groos’s The Play of Animals was the only book-length treatment of animal play from an evolutionary perspective, and his The Play of Man is even today the only attempt at a full account of human play from that perspective.

Groos’s Practice Theory of Play

One way that Groos was ahead of his time was in his understanding of ways that heredity and experience interact in the development of behavior. Prior to Groos, and even for some time after, most psychologists drew a sharp distinction between instincts, which are behaviors rigidly programmed by the nervous system and triggered by specific environmental stimuli, and learned behaviors, which are shaped by experience. Groos realized, as did only a few others at his time (notably James Mark Baldwin and William James), that this is a false distinction, at least for mammals.

Mammals come into the world with a large, inborn repertoire of natural drives and behavioral tendencies, which can be manifested in various ways and are very much influenced by the animal’s experience in the world. Groos, like Baldwin and James, referred to these drives and tendencies as instincts. For example, all mammals have instincts to seek out and consume food, to defend themselves against aggressors, to seek mates for reproduction, to care for their young, and so on. The list can be quite long. But these tendencies are plastic, moldable, not fully formed by heredity.

Groos’s insight was to recognize that mammals must, to varying degrees, learn to use their instincts. To become effective, the instinctive tendencies must be practiced and refined. Play, according to Groos, is the primary means of such practice. Stated differently, play is essentially an instinct to practice other instincts. He also noted that mammals come into the world with incompletely formed neuromuscular systems, which must be exercised and strengthened through activity, that is, through play.

Groos (1898, p 23-24) wrote: “Without [play in youth] the adult animal would be but poorly equipped for the tasks of life. He would have far less than the requisite amount of practice in running and leaping, in springing on his prey, in seizing and strangling the victim, in fleeing from his enemies, in fighting his opponents, etc.  The muscular system would not be sufficiently developed and trained for all these tasks.  Moreover, much would be wanting in the structure of his skeleton, much that must be supplied by functional adaptation during the life of each individual, even in the period of growth.”

In an argument against the then-prevailing theory that young animals play because they have a lot of energy that must somehow be released (the surplus energy theory), Groos (1898, p 75) wrote: "Animals cannot be said to play because they are young and frolicsome, but rather they have a period of youth in order to play; for only by doing so can they supplement the insufficient hereditary endowment with individual experience, in view of the coming tasks of life.”

Evidence Supporting Groos’s Practice Theory, as Applied to Animals

Groos’s theory allows us to make sense of the patterns of play seen throughout the animal world. For starters, it explains why young animals play more than do older ones of the same species; they play more because they have more to learn.

It also explains why mammals play more than do other classes of animals. Insects, reptiles, amphibians and fishes come into the world with rather fixed instincts; they don't need to learn much in order to survive, given their ways of life, and there is little if any evidence in them of play. Mammals, on the other hand, have more flexible instincts, which must be supplemented and shaped through learning and practice provided by play.

The theory also explains the differences in playfulness found among different orders and species of animals. Among mammals, primates (monkeys and apes) are the most flexible and adaptable order, with the most to learn, and they appear to be the most playful of all animal orders. Also among mammals, carnivores (including the dog-like and cat-like species) are generally more playful than herbivores, probably because success in hunting requires more learning than does success in grazing. Aside from mammals, the only other animal class in which play has been regularly observed is that of birds. The most playful birds are the corvids (crows, magpies, and ravens), raptors (hawks and their relatives), and parrots. These are all long-lived birds, with larger brain to body weight ratios than other birds, which exhibit much flexibility and cleverness in their social lives and ways of obtaining food. (Evidence for these species differences can be found in Burghart, 2005, and Fagan, 1981.)

The idea that play's purpose is to promote skill learning helps us to understand species differences in types of play as well as in amounts of play. As Groos pointed out, to a considerable degree, you can predict what an animal will play at by knowing what skills it must develop in order to survive and reproduce. Lion cubs and the young of other predators play at stalking or chasing and pouncing; zebra colts, young gazelles, and other animals that are preyed upon by lions and such, play at dodging and fleeing; young monkeys play at swinging from branch to branch in trees.

The theory also predicts sex differences in play. Among species in which males fight one another for access to females, young males engage in more play fighting than do young females (Meaney et al, 1985). And, at least among some species of primates, young females, but not young males, engage in much playful care of infants (e.g. Kahlenberg & Wrangham, 2010).

In a chapter on the evolutionary functions of play for an academic book (Gray, 2019), I summarized some more recent animal research supporting Groos’s practice theory. It includes evidence (a) that playful activity tends to be timed to occur during periods when a young animal’s neuro-behavioral systems are undergoing the most rapid change; (b) that young animals generally stop playing at a particular activity when they become highly skilled at that activity; and (c) that those young animals that play the most are most likely to survive into adulthood (in research conducted with ground squirrels, marmosets, and bears).

Application of Groos’s Theory to Humans

I’m going to pursue the practice theory as applied to humans more fully in Letter #5, but here is a taste.

In The Play of Man, Groos pointed out that everything he said about animal play also applies to humans, in ways that provide even further evidence for the practice theory. He pointed out that human beings, having much more to learn than do other animals, play much more, and in a greater variety of ways, and over a longer developmental period, than do other animals. Young humans everywhere, when free, play at all the kinds of skills that human beings must everywhere develop in order to survive and thrive.

He also pointed out that human beings, much more so than the young of any other species, must learn different skills depending on the unique culture in which they develop.  Therefore, he argued, natural selection led to a strong drive, in human children, to observe the activities of their elders and incorporate those activities into their play. Children in every culture play at the general categories of activities that are essential to people everywhere, and they also play at the specific variations of those activities that are unique to their native culture.

Groos modestly called his theory a theory of play, but think it is even more than that. It is a theory of education. By observing others in their community and incorporating what they observe into their play, children educate themselves. There will be more about this idea in future letters.

Notes

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References

Burghardt, C. (2005). The genesis of animal play: Testing the limits.  Cambridge, MA: MIT Press.

Fagan, R. (1981). Animal play behavior. New York: Oxford University Press.

Gray, P. (2019). Evolutionary functions of play: Practice, resilience, innovation, and cooperation.  In P. K. Smith & J. Roopnarine (Eds.), The Cambridge handbook of play: developmental and disciplinary perspectives (pp 84-102). Cambridge, UK: Cambridge University Press.

Groos, K. (1898). The play of animals. New York: Appleton.

Groos, K. (1901). The play of man. New York: Appleton.

Kahlenberg, S. M., & Wrangham, R. W. (2010). Sex differences in champanzees’ use of sticks as play objects resemble those of children.  Current Biology, 20, R1067-R1068.

Meaney, M. J., Stewart, J., & Beatty, W. W. (1985). Sex differences in social play: The socialization of sex roles.  Advances in the Study of Behavior, 15, 1-58.

Some portions of this letter come verbatim from my book Free to Learn.