Imitation, Pretend Play, and Childhood: Essential Elements in the Evolution of Human Culture?

Introduction

• Human culture is different from the “cultural” characteristics of other animals.
• Childhood as a step in the life cycle was critical to the evolution of the human cultural mind.
• Two complementary features of childhood: imitation and play.
• Children imitate adults and copy unnecessary and arbitrary actions.
• Children construct rules and meanings that exist purely because the players agree they “exist.” Thus play rehearses cultural practices.
• These forms of imitation and play represent a foundation upon which human culture flourished and that neither are prevalent in nonhuman animals.
• Childhood emerged relatively late in human evolution.
• Keywords: social learning, dental ontogeny, Oldowan, Acheulian, Mousterean, lithic technology

Culture in Chimpanzees and Orangutans

• Groundbreaking work by Whiten and colleagues (1999) collated behaviors exhibited by wild chimpanzees in seven long-term study sites.
• Behaviors were grouped into “patterns” deemed customary or habitual.
• Patterns existed in some communities but not others, discounting ecological explanations and intraspecific genetic variation.
• Example: Chimpanzees from Bossou use petioles as pestles to pound at the center of palm crowns to create a cavity and extract fibrous product.
• Chimpanzees from the Tai Forest, despite having the same palm trees, do not engage in pestle-pounding.
• Whiten et al. identified 39 such patterns.
• Van Schaik and colleagues (2003) identified 19 behavioral variants in orangutans using the geographical analysis approach.
• When defined as “the possession of multiple traditions, spanning different domains of behavior, such as foraging techniques and social customs” (Whiten & van Schaik, 2007, p. 605), it can be argued that our closest living relatives thus have some form of rudimentary culture.
• Rudimentary: Multiple, varied aspects of human day-to-day behavior are culturally driven in a way that is not evident in these animals or any other.

Human Culture

• Homo sapiens are the world’s cultural species par excellence.
• Focus has turned to identifying those elements that have been selected over the course of our evolution to find us shaped into the ultracultural being we are today (see Whiten, Hinde, Laland, & Stringer, in press).
• Debate across a broad range of disciplines has led to a rich and diverse literature that features comparisons between the social and cognitive abilities of human children and great apes at its core.

Imitation as the Ultimate Cultural Transmission Device

• For any behavior to be considered “cultural” it must propagate in a social group.
• Scholars of cultural evolution have searched for potential mechanisms by which behavior can spread socially in a manner that would enable stable habits and traditions to emerge.
• Imitation is commonly touted as the most likely candidate (e.g., Boyd & Richerson, 1985; Gergely & Csibra, 2005; Tomasello, 1999; Whiten, 2005).
• This view is challenged by those who maintain that the role of imitation in the development and transmission of culture is limited or that there must be multiple other learning processes at play (e.g., Caldwell & Millen, 2009; Claidière & Sperber, 2010; Galef, 1988; Henrich & McElreath, 2003; Heyes, 1993; Sterelny, 2006).

Overimitation

• Horner and Whiten (2005) demonstrated overimitation: Children and chimpanzees were shown how to obtain a reward from a novel box.
• A bolt on the top of the box was first removed, revealing a hole into which a stick was poked. A door located on the front of the box was then opened, and the stick was used to extract the reward.
• With the opaque box, both chimpanzees and children copied all demonstrated actions.
• When a transparent box was substituted, chimpanzees ignored the first action (stick in top hole) and copied only the insertion of the tool into the front hole.
• Children replicated the model’s entire sequence of actions, including the irrelevant insertion of the stick into the top hole.
• Subsequent studies have shown that children consistently copy all actions used by an adult when solving a novel task, even when the acts can be seen to have no causal relevance to the demonstrated outcome and even when they may actually compromise success (Kenward, Karlsson, & Persson, 2011; Lyons, Young, & Keil, 2007; McGuigan & Whiten, 2009; Nielsen, 2006; Nielsen & Blank, 2011).
• Nielsen and Tomaselli (2010) showed that children replicated irrelevant actions, whether they had been raised in a large, industrialized, Western city or in remote Bushman communities of the Kalahari Desert.

Advantages of Overimitation

• Overimitation may come with certain advantages that outweigh costs such as time and energy expenditure.
• Tools and objects often lack perceptual information about the goal(s) for which they are being used.
• Their uses are cognitively ‘opaque,’ making it challenging for novices to identify which actions or behaviors are relevant and which are incidental (Gergely & Csibra, 2006; Lyons et al., 2007).
• Adopting a strategy based around exact copying may have fewer costs than attempting to selectively choose relevant components.
• Directly replicating others also affords the rapid acquisition of a vast array of skills that have been developed and passed on over multiple generations, avoiding the potential pitfalls and false end-points that can come from individual learning.

Causal vs. Status Functions

• When we use, design, or create objects instrumentally (i.e., as tools) their functions are predominantly determined by an interaction between the objects’ physical properties and the constraints of the user.
• Objects can thus have ‘causal usage functions’ (Rakoczy, 2007; Searle, 1995).
• Other objects have functions assigned to them purely by virtue of collective practice.
• These objects have what are called “status functions” and they are a pivotal component of any human culture (Rakoczy, 2007; Searle, 1995).
• Children’s propensity for replicating all of the actions shown to them by adults, even those that are apparently unnecessary, provides a mechanism by which status functions can be transmitted intergenerationally.
• Overimitation can thus be seen as indispensable in the acquisition of arbitrary, conventional skills and when identifying with and aligning oneself with one’s cultural in-group.

Overimitation and Human Culture

• Great apes show evidence of culture but it is of a rudimentary nature relative to the richness, complexity, and pervasiveness of human culture.
• Overimitation affords a vast array of information and skill to be passed from one generation to the next, and something on which the arbitrary aspects of human culture can find a foothold.
• Critically, although imitation has been documented in great apes, overimitation has not (Horner & Whiten, 2005; Nagell, Olguin, & Tomasello, 1993; Nielsen & Susianto, in press; Tennie, Call, & Tomasello, 2006).
• Hobaiter & Byrne (2010) reported infrequent copying of unnecessary gestural actions in chimpanzees.
• Comparing humans with apes remains one of the most efficient and effective approaches to understanding what makes us who we are.
• If apes don’t routinely engage in high-fidelity imitation, can we find evidence in the fossil record to identify when a propensity for such behavior might have emerged subsequent to divergence from our last common ancestor?

Social Learning and Paleolithic Stone Tool Technology

• Artifacts offer a durable source of information about ancestor behavior (Foley & Lahr, 2003; Stout & Chaminade, 2009).
• Change in stone-tool technologies sheds light on when in our evolutionary past certain behaviors may have emerged.

Oldowan Industrial Complex

• The first definitive evidence for early hominin tool use comes from what is referred to as the Oldowan Industrial Complex (see Figure 1A), which comprises mostly sharp-edged flakes and the cores from which they came (Monnier, 2006).
• Dating from around 2.6 –1.4 million years ago (mya—although see McPherron et al., 2010), and associated with Australopithecines and early Homo (see Figure 2), these tools have been deliberately flaked through percussive blows.
• These tools were likely made through individual trial and error learning, with their shapes largely controlled by the properties of the raw materials used (Ambrose, 2001; Mithen, 1999; Wynn & McGrew, 1989).
• There is no sign in these tools that they have been produced through a process relying on high fidelity imitation.
• The lack of consistent patterns of assembly indicate that Oldowan tools “reflect least-effort strategies for obtaining large sharp-edged flakes from available raw materials, rather than culturally determined stylistic traditions” (Ambrose, 2001, p.1749; see also Isaac, Harris, & Marshall, 1981/1996; Toth, 1985).

Acheulian Industrial Complex

• At approximately 1.6 mya, the Acheulian Industrial Complex appears (Asfaw et al., 1992; Chazan et al., 2008; Isaacs & Curtis, 1974).
• Associated with Homo ergaster and Homo erectus (see Figure 2), these stone tools are commonly exemplified by the teardrop-shaped bifacial handaxe (Figure 1B) signaling one of the most important steps in human technical and social evolution (Porr, 2005).
• Bifaces present novel advances over Oldowan tools, including application to multiple uses, economy of raw material use, and the potential utility of resharpening flakes—each of which are especially important in high mobility situations (Hayden, Franco, & Spafford, 1996).
• Standing out as a major departure from the Oldowan Industrial Complex, the Acheulian lithic industry is characterized by a regularity of design that persisted for hundreds of millennia (Hill, Barton, & Hurtado, 2009).
• Construction of Acheulian tools demands considerable devotion of time and effort (Stout, 2002).
• This, when coupled with the adherence to a common form, suggests involvement of the constant monitoring and correcting of achieved results, which had to be replications of already existing objects.
• Imitation involves reproducing an observed outcome using the same actions the model used with an understanding of the intentions behind the actions (Tomasello, 1990).
• For a number of authors, the Acheulian Industrial Complex thus presents overwhelming evidence for the social transmission of information via this mechanism (Mithen, 1999; Porr, 2005; Shipton, 2010).
• As Porr (2005) has argued, “it was the sequence of acts and the practical mastery of production that was powerful and not the finalized object alone” (p. 80).
• If actions are viewed in purely instrumental terms, overimitation, which involves the reproduction of redundant actions, seems not to adhere to the aforementioned definition (it is challenging to identify intention behind actions that are obviously causally irrelevant).
• However, when modeled actions are also seen as a means of conveying social and/or culturally appropriate information (Carpenter, 2006; Nielsen, 2008; Over & Carpenter, in press; Uzgiris, 1981) the behavior can fit the definition.
• In this context it is notable that the kinds of butchery and other tasks that handaxes are thought to have been used for can be just as efficiently achieved using less refined artifacts (Kohn & Mithen, 1999).
• Handaxes are also puzzlingly symmetrical (Kohn & Mithen, 1999; Lycett, 2008).
• This suggests the possibility that unnecessary actions and pro- cesses were being transmitted socially.
• Thus, in the tool kit of the Acheulian we perhaps find not only evidence of imitation but also the first signs of a mind predisposed to overimitate.
• For more than a million years during the Acheulian the appearance of “new” tools is at best sporadic (Goren-Inbar, 2011; Stout, 2011).
• Indeed the rather repetitive and monomorphic production of Acheulian handaxes is considered by some to suggest a general lack of technological innovation (Foley & Lahr, 2003; Hill et al., 2009).
• Overimitation may be viewed as fertile ground for the arbitrary aspects of human culture to flourish and a mechanism by which a vast array of information and skill can be passed from one generation to the next.
• It may be argued that there is evidence of it emerging in the Acheulian.
• A key feature of human culture is not only that skills are readily transmitted from one generation to the next but that such skills are modified and improved on, sometimes at a remarkable pace.

Example of Technological Innovation

• Cle´ment Ader made the first manned, powered, heavier-than-air flight in 1890 (Schmidhuber, 2003).
• It took less than 80 years to go from his bat-wing monoplane to a craft capable of putting Neil Armstrong and Edwin Aldrin on the moon.
• Innovation must also be a core feature of the human cultural mind, something that becomes more evident as we move through the archeological record.

Social Learning and Innovation in the Middle Paleolithic

• As recently as 400,000 years ago (400 kya), Homo heidelbergensis flintknappers were producing very thin bifaces, with three-dimensional symmetry (Coolidge & Wynn, 2009).
• They were also competent practitioners of the Levallois technique whereby a flake is shaped and refined before being struck from its core.
• During this period, stone tools were becoming increasingly refined and knappers increasingly better at producing them.
• Developments in the prepared core techniques associated with heidelbergensis unfolded over tens of thousands of years—a rate that according to Coolidge and Wynn rules out conscious experimentation and creativity (Coolidge & Wynn, 2009; Wynn & Coolidge, 2004).
• Thus, even in the lithic traditions exemplified by heidelbergensis, a species who lived a comparatively short time ago, the kinds of advances in technological innovation that would signal a clear shift toward something akin to the modern cultural mind remain elusive.

Emergence of Mousterian tool kit

• Around 300 kya saw an order-of-magnitude increase in technological complexity resulting in the emergence of the Mousterian tool kit, commonly associated with Homo neanderthalensis, late archaic humans, and anatomically modern humans.
• Tools now represent clear specializations for skinning and preparing meat, hunting, and woodworking (Figure 1C).
• The lithic fossil record transitions from a dominance of handaxes to blades (flakes with a breadth: length ratio >= 0.5).
• Blades offer a more efficient use of raw material than either core or flake tools and require an impressive level of skill to manufacture (McBrearty & Brooks, 2000).
• This epoch is also witness to the emergence of hafting, whereby a blade is fitted to a handle using some kind of binding material or adhesive, typically after having been modified by thinning at the butt.
• Interregional variation also becomes evident.
• Assemblages found at Gorgora on Ethiopia’s Lake Tana have markedly subtriangle points, those from Midhishi in northern Somalia show Levallois points and blades at Gademotta in the Ethiopian Rift Valley take on a pointed leaf-shaped form (Clark, 1988).
• We thus now see not only more rapid leaps in innovation but the emergence of clearly identifiable regional and stylistic variants indicative of true cultural traditions and culture areas (Ambrose, 2001; McBrearty & Brooks, 2000).

Human Social-Cultural Cognition

• According to Herrmann and colleagues (2007) humans’ “especially powerful skills of social-cultural cognition early in ontogeny. . .serve as a kind of “bootstrap” for the distinctively complex development of human cognition in general” (p. 1360; see also van Schaik & Burkart, 2011; Whiten & van Schaik, 2007).
• In line with this, it may be that the mind which gives rise to sophisticated cultural behaviors emerges only after being first established in the developing child.
• This, of course, relies on the existence of a childhood in the first place.

Human Childhood: A Unique Life History Phase

• An animal’s life history is typically defined by the strategic allocation of its energy toward growth, maintenance, reproduction, raising offspring to independence, and avoiding death (Hochberg, 2009).
• For mammals, these events incorporate strategies of when to be born, when to be weaned, when to stop growing, when to reproduce, and when to die in the best way as to increase fitness (B. H. Smith, 1992).
• For mammals, birth is followed by a period of infancy that is characterized by the appearance of deciduous teeth and all or some nourishment being provided by the mother via lactation.
• For the majority of mammals this period transitions seamlessly into adulthood.
• However, many species of monkeys and apes, as with other highly social mammals, postpone puberty and insert a phase of juvenile growth between infancy and adulthood.
• The onset of this juvenile period coincides with eruption of the first permanent molars (B. H. Smith & Tompkins, 1995), with individuals now having to forage for food and otherwise care for themselves with little or no assistance from others (Coelho, 1986; Perieira & Altmann, 1985).
• In chimpanzees this juvenile period is extended and offspring are dependent on their mothers for about 5 years (Gavan, 1971; Kaplan, Hill, Lancaster, & Hurtado, 2000; Watts & Gavan, 1982).
• Human life history is different from the tripartite postnatal growth of infancy, juvenile growth, and adulthood shown by other primates (Bogin, 1988, 1990; Bogin & Smith, 1996; Hochberg & Albertsson-Wikland, 2008).
• Humans have a shorter infancy with breast-feeding usually discontinued at a median of 36 months of age in preindustrial societies (Dettwyler, 1995; Kaplan et al., 2000; Sellen & Smay, 2001).
• Coincident with weaning are changes in growth hormone regulation, particularly the GH–IGF-I endocrine axis and target cell responsiveness, with growth rate leveling off at about 5 cm per year (Hochberg & Albertsson-Wikland, 2008; Wit & Van Unen, 1992).
• Stabilization of growth rate in this way is rare in mammals (Brody, 1945; Tanner, 1962).
• Given the high metabolic demands of a brain that is still growing rapidly, weaning at this young age places a great nutritional burden on offspring.
• Three-year-olds are not typically mature enough to prepare their own food and are too limited by deciduous dentition and a small gastrointestinal tract to consume the adult diet.
• In various hunter–gatherer societies the solution to this problem is for older members of the social group to provide specially prepared foods that are high in energy and nutrients until self-care becomes possible (Kaplan et al., 2000; Locke & Bogin, 2006).

Six Traits Characterizing Childhood

• According to Locke and Bogin (2006) the period after the cessation of breastfeeding in humans is characterized by the following six traits:
  1. Slow and steady rate of body growth and relatively small body size;
  2. Large, fast-growing brain;
  3. Higher resting metabolic rate than any other mammalian species;
  4. Immature dentition;
  5. Dependence on older people for care and feeding;
  6. Motor and cognitive advances.
• Locke and Bogin (2006) argue that no other living species has this entire suite of features, features that correspond to a developmental period they label “childhood.”
• This extended period and the developmental patterns of the human brain associated with it provide an opportunity for extensive learning and for sophisticated cultural behaviors to develop (Bogin, 1990; Roberts, 2001).

Childhood and Dental Ontogeny

• If the emergence of childhood as a life-history stage is foundational to the advances in cultural cognition that have taken us away from the rudimentary behavioral traditions found in our primate cousins, when might this have happened?
• Contemporary attempts to answer questions of biological development have relied on brain ontogeny, fossil ontogeny, and molecular evidence in attempts to chart when in hominin evolution a specific pattern of ontogeny arose for the first time (Zollikofer & Ponce de Leon, 2010).
• In the last decade the greatest advances have been made using dental ontogeny.
• Among primates, life-history traits, such as cessation of brain growth, adolescent growth spurt, and age at first reproduction, are tightly associated with dental development (Dean et al., 2001; Zollikofer & Ponce de Leon, 2010).
• A modern human-like sequence of dental development, as a proxy for the pace of life history, is regarded as one of the diagnostic hallmarks of our species (Dean et al., 2001; B. H. Smith & Tompkins, 1995).
• During the last three decades, the most common method used to address questions of hominin growth and development has been the study of the duration and the sequence of dental development.
• Daily deposits of cells called ameloblasts form enamel, the hard outermost layer of teeth.
• These daily deposits can be seen as incremental markings when viewed under a microscope, and counts of these markings in the teeth of individuals with known dates of birth and death match very closely with the number of days of life (Antoine, Hillson, & Dean, 2009; Dean, 2010).
• Superimposed on this daily rhythm is a coarser, more prominent marking called the striae of Retzius that when viewed in cross- section appear as concentric rings, much like annual rings on a tree.
• Counting the striae enables evaluation of a specimen’s age of death, thereby permitting dental eruption sequences to be calibrated against an absolute time scale (Dean, 2006).
• This means that the period of maturation in fossil primates can be reconstructed and compared in real time with living primates.

Dental Analysis Example

• Smith and colleagues (T M Smith et al., 2007) analyzed the lower right lateral incisor, lower left canine, and mesiobuccal cusp of the lower left molar of an early Homo sapiens juvenile from Morocco dated at 160kya.
• Using x-ray synchrotron microtomography, analysis based on the striae of Retzius indicated that the age of death of this specimen was 7.78 years (2839 days), with virtual extraction revealing that both premolars and the second permanent molar had completed crown formation and had just begun root formation.
• This pattern of eruption and dental development occurs in modern European populations between 7.2 and 7.6 years, indicating that this Middle Pleistocene ancestor had an extended period of development similar to average modern European children.
• Smith et al. maintain that this indicates a “childhood” life stage and along with it “the advent of corre- sponding social, biological, and cultural changes necessary to support highly dependent children with prolonged opportunities for social learning in childhood” (p. 6132).

Dental Development in Lower Paleolithic Hominins

• There is a general consensus among paleoanthropologists that dental development in lower Paleolithic hominins, from Ardipithecus ramidus (Suwa et al., 2009), through Australopithecus afarensis (Lacruz & Ramirez Rozzi, 2010; B. H. Smith, 1986) to Homo erectus (Dean, 2000; Dean et al., 2001), follows a chimpanzee-like timing.
• Based on microscopic analysis of growth patterns in fossil teeth, there is scant evidence to suggest a childhood was present before 1.5 mya.

Dental Development in Neanderthals and Homo antecessor

• Interpretation of Homo neanderthalensis teeth are more equivocal (Bayle et al., 2010; Ramirez Rozzi & Bermudez de Castro, 2004; Zollikofer & Ponce de Leon, 2010).
• Some conclude that Neanderthal dental development indicates that “a prolonged childhood and slow life history are unique to Homo sapiens” (T. M. Smith, Toussaint, Reid, Olejniczak, & Hublin, 2007, p. 20220), whereas others argue that the data “firmly place key Neanderthal life history variables within those known for modern humans” (Macchiarelli et al., 2006, p.748).
• Analysis of a juvenile Homo antecessor mandible, dated between 800 and 960 kya, suggests a prolonged childhood in the range of the variation of modern humans (Burmu`dez de Castro et al., 2010; see also Gomez-Robles, Bermudez de Castro, Martinon-Torres, & Prado-Simon, 2011).
• The extent to which a childhood life-stage emerges coincident with the appearance of the Mousterian tool kit thus currently remains unclear.
• It is possible that childhood preceded Mousterian lithic construction or emerged commensurate with it.
• If the evidence for childhood in Homo antecessor withstands scrutiny it would suggest childhood is not sufficient for technological innovation to blossom (antecessor appear to have used only Oldowan-like stone tools).
• Childhood as a life history stage postdates the emergence of Acheulian stone tools, where there are hints of a social learning repertoire including something like overimitation.
• Once adults had begun copying others by focusing on means over ends, the emergence of childhood would have provided a platform for this attitude toward adopting others’ behavior to be firmly established.
• Childhood opens the possibility for creativity to flourish in a new way, fostered through one of the foundational elements of the human sociocognitive mind: pretend play.

Pretence as a Springboard for Innovation

• Every family of mammals shows some evidence of play in some species (Burghardt, 2005).
• In humans, play emerges early in ontogeny and in its initial expression is characterized by the functional treatment of objects where infants attend to cause and effect relations with objects, focusing on literal and intended uses, such as pushing a toy on wheels or placing building blocks together.
• Toward the end of the second year infants begin to demonstrate an interest in applying their knowledge base to symbolically manipulate objects and their properties, and to allow their imagination, rather than the stimulus itself, to dominate their behavior: They begin to pretend (Harris, 2000; Leslie, 1987).
• That is, their play starts to involve the symbolic, nonliteral transformation of the here-and-now whereby the world, in the context of a play sequence, gets treated contrary to reality.
• With development children’s pretence incorporates ever more complex and cognitively demanding routines, as simple behaviors directed toward the self translate to more sophisticated actions involving sequences and object substitution.
• Pretending children can discover discovering.
• In order to pretend children must imagine something that is currently not true then behave as if it were.
• By pretending children thus develop a capacity to generate and reason with novel suppositions and imaginary scenarios, and in so doing may get to practice the creative process that underpins innovation in adulthood (Carruthers, 2002, 2006; Pellegrini, Dupuis, & Smith, 2007).
• In the imaginative process of pretending children can also recombine actions and behaviors they have observed adults performing, thereby finding a release from the high fidelity sequence copying that happens in direct adult-child transmission.

Evidence Linking Pretence and Innovation

• Link between pretence and innovation has a long pedigree (Almy, 1967; Bruner, 1972; Lieberman, 1977; Piaget, 1962; Sutton-Smith, 1967), yet it remains one with little conclusive accompanying evidence.
• Support comes from the literature on children with autism who display impairments in both pretence (Jarrold, 2003) and creativity (Craig & Baron-Cohen, 1999).
• Evidence also comes from children who grow up in Old Order Mennonite communities, where the pretense of these children predominantly consists of acting out real-life roles with little integration of imaginary objects (Carlson, Taylor, & Levin, 1998).
• Children with imaginary companions show a strong inclination toward engaging in fantasy-themed play and show higher levels of creativity than children who do not have imaginary companions (Hoff, 2005; Schaeffer, 1969; Taylor, 1999).
• Adults who recall having an imaginary companion as a child have also been shown to outperform those who do not on a variety of creativity indices (Gleason, Jarudi, & Cheek, 2003; Kidd, Rogers, & Rogers, 2010; Taylor, Hodges, & Kohanyi, 2003).

Dansky and Silverman Study

• Dansky and Silverman (1973) gave a group of 4- to 6-year-old children 10 minutes to play with a set of objects. Another group of children watched an adult perform four tasks with these objects and were subsequently asked to imitate the experimenter’s actions. A third group was given a box of crayons and four pictures to color in.
• After the experimental treatments each child was asked to suggest alternate uses for the four stimulus objects. Responses were scored according to whether they were standard or nonstandard.
• Children in the play condition produced significantly more non- standard responses for each object (for replication see Dansky, 1980; Dansky & Silverman, 1975; Li, 1978; for criticism see P. K. Smith & Whitney, 1987).

Shared Pretence

• Irrespective of the veracity of the afore-proposed nexus between pretence and innovation there is another aspect to pretending that may be critical in the development of human culture—that of sharing pretence.
• When children pretend together they often make up the content of their pretend environment as they go, refining and redescribing it as becomes necessary.
• According to Rakoczy (2007, 2008), there are convincing parallels between status function and what occurs in joint pretence.
• Status functions can be expressed by the formula “X counts as a Y in context C.”
• In pretence, a small wooden block (X) may count as a fish (Y) in the context of an ongoing fishing game (C).
• Children will track and respect the fictional status assignments of their play partners, enter into shared pretence based on these stipulations, and perform inferentially and contextually appropriate acts (Harris & Kavanaugh, 1993; Rakoczy, Tomasello, & Striano, 2004; Wyman, Rakoczy, & Tomasello, 2009a, 2009b).

Pretend Play and Social Realities

• It is possible that pretend play is a starting point for children to develop social realities, as pretend play itself consists of rules that exist purely because the players agree they “exist” (Rakoczy, 2008).
• Pretend play is a human universal (P. K. Smith, 2010).

Pretence in Nonhuman Apes

• On a purely cognitive level pretence should also be evident in nonhuman apes.
• Based on their comprehensive survey of the evidence for a variety of cognitive achievements, Suddendorf and Whiten (2001; Whiten & Suddendorf, 2007) have convincingly argued that great apes have the mental representational ability to pretend.
• One of the most famous reports comes from the encultured chimpanzee Viki (Hayes, 1951) who was fond of real pull-toys.
• She spontaneously started acting as if she had a pull-toy, despite the fact that she did not. However, this imaginative play stopped abruptly after a few weeks and did not return.
• This is reflected in an analysis of videotaped behavior by three captive bonobos and two captive chimpanzees (Lyn, Greenfield, & Savage-Rumbaugh, 2006).
• From 99 hours of tape, 27 possible examples of pretence were identified—with only six of these considered convincing by conservative estimates (Gomez, 2008).
• By the time they are 4 years old children are spending as much as one quarter of their free time pretending (Haight & Miller, 1992).
• As Suddendorf and Whiten (2001) point out, pretence in apes “appears in the form of relatively rare and fleeting signs of the necessary imaginative capacity, rather than an obvious everyday manifestation” (p. 637).
• There is a stark gap in the expression of pretend behavior between our closest living primate cousins and us.

Ancestor Propensity for Pretending

• Signs from our Homo ancestors of a propensity for pretending are unfortunately fragile and largely rest on evidence of potentially symbolic behavior such as carvings, engravings on artifactual pigment, and personal ornaments (Bar-Yosef Mayer, Vandermeersch, & Bar-Yosef, 2009; Bouzouggar et al., 2007; Conrad, Malina, & Mu¨nzel, 2009; d’Errico, Henshilwood, Vanhaeren, & van Niekerk, 2005; d’Errico et al., 2009; Henshilwood, d“Errico, & Watts”, 2009; Marshack, 1989; Texier et al., 2010).
• Tracking the possible evolutionary unfolding of our pretending mind thus remains remarkably challenging.

Conclusion

• The human cultural mind is one that must be able to adapt to innumerable skills, actions, behaviors, and objects, some of which will be entirely arbitrary.
• It must be capable of accessing information, skills, and strategies that have built up over generations.
• And it must generate novel ideas and solutions.
• Overimitation and pretend play provide ground in which such a mind can find root.
• Overimitation provides for the rapid intergenerational transfer of a vast array of information and skill and a foundation upon which the capricious aspects of human culture can be built.
• Pretence introduces room for innovation, imagination, and a realm in which the understanding and appreciation of social realities can take shape.
• The prolonged growth of childhood maximizes maturational differences between adult teachers and young learners, differences that facilitate the pedagogical process and enable overimitation to flourish (Bogin, 1990; Csibra & Gergely, 2009; Gergely & Csibra, 2005, 2006; Gergely, Egyed, & Kiraly, 2007; Tennie et al., 2009) while providing time and opportunity for pretending skills to be acquired (Rakoczy, 2006, 2008).
  -There is evidence suggesting that a propensity for overimitation had begun to permeate the hominin mind around 1.5 mya, but it is not until the middle Paleolithic that evidence begins to accrue for true cultural creativity, for symbolism, and for childhood.

Cultural Mind

• A cultural mind reflecting our own may not have emerged until many millennia after we diverged from a common ancestor.
• The arguments outlined in this article are speculative and lack the critical evidence that would render them more conclusive.

Threefold Arguments:

1. Imitation and pretend play have been and are critical developmental domains in the evolution of human culture.
2. These domains became firmly established in the human mind and flourished only because the Homo line developed an extended childhood as a life stage.
   3