Teaching and norm-based cooperation

Here, I suggest that a critical step in getting large-scale cooperation off the ground was the evolution of widespread teaching. In fact, teaching is an act of cooperation (Fogarty, Strimling, & Laland, Reference Fogarty, Strimling and Laland2011). Cooperation is defined as behavior that provides a benefit to another individual (the ‘recipient’) and that was favored by natural selection because of its beneficial effect on the recipient (West, El Mouden, & Gardner, Reference West, Griffin and Gardner2007). Teaching, in turn, is costly information donation; it is behavior that functions to impart knowledge (Fogarty et al., Reference Fogarty, Strimling and Laland2011). These definitions clarify how teaching relates to cooperation. In the case of teaching, the ’benefit’ to the recipient is ’useful knowledge’.

My laboratory has investigated the evolution of teaching using mathematical models. Our theoretical work suggests that a generalized form of teaching coevolved in humans with our capacity for cumulative culture (Fogarty et al., Reference Fogarty, Strimling and Laland2011). The analysis implies that teaching is widespread in humans because cumulative cultural knowledge builds up over time, leaving otherwise difficult to learn, high-fitness information available in the population for tutors to impart to their pupils (Fogarty et al., Reference Fogarty, Strimling and Laland2011). This work sheds light on the respects in which human cooperation is unique. Clearly “complex and unique mechanisms to enforce cooperation have arisen in humans, such as contracts, laws, justice, trade and social norms...” (West et al., Reference West, El Mouden and Gardner2011), and I submit that all of these mechanisms require teaching in order to operate.

Much human cooperation would seemingly equally require a capacity for language, but there are good reasons for thinking that the origin of language is also tied in with teaching and cumulative culture (Laland, Reference Laland2017). Language may initially have evolved to enhance the efficiency and accuracy of teaching and, even if it originated for some other reason, language could certainly have been applied in this context. In this article I argue that human cooperation may be unusually extensive as a result of cumulative culture and may be uniquely reliant on important mechanisms that are absent or less-frequently observed in other species: specifically, teaching, language and imitation.

Two findings to emerge from our investigations of the evolution of teaching were firstly that the likelihood of teaching increases with the degree of relatedness between tutor and pupil, and secondly that it decreases with the costs of teaching (Fogarty et al., Reference Fogarty, Strimling and Laland2011). Empirical data from human populations support these conclusions (Kline, Boyd, & Henrich, Reference Kline, Boyd and Henrich2013). Accordingly, we can envisage the kind of widespread, generalized teaching observed in humans to have initially appeared amongst close relatives: parents teaching foraging skills to offspring, or siblings helping each other learn tool making, for instance. Initially, then, a kin-selection mechanism was relevant. Yet, without some rudimentary form of language, the teaching of more distant relatives would rarely have been economical, as the inclusive fitness benefits to the tutor would be modest. By simultaneously reducing the costs and incrementing the accuracy of teaching, the advent of language would have allowed teaching to spread to more distantly related individuals, including to small groups such as hominin hunter-gatherer bands. This teaching may have sufficed to allow individuals in small bands to teach each other specific roles in coordinated tasks, such as hunting antelope, or driving off predators, thereby broadening the scale of kin-based cooperation.

While many animals are proficient at social learning, and some, such as primates and cetaceans, have behavioral traditions, in contrast teaching is rare in animals (Hoppitt & Laland, Reference Hoppitt and Laland2011). Most animal teaching merely creates enhanced opportunities for learning in the pupil (Caro & Hauser, Reference Caro and Hauser1992), as when meerkats provide pups with disabled scorpions (Thornton & McAuliffe, Reference Thornton and McAuliffe2006). However, in rare cases, animals show hints of ’coaching’, in which the response of the tutor functions to encourage or discourage the pupil’s behavior (Caro & Hauser, Reference Caro and Hauser1992), as when mother hens attract their chicks away from food that she believes is unpalatable (Nicol & Pope, Reference Nicol and Pope1996). Such error correction is, of course, a feature of much contemporary human teaching (although humans also teach by more subtle means). It follows that at some juncture in our history, our ancestors began systematically to correct the behavior of the individuals that they taught, in the process shifting their society away from reliance on mere conventions and towards governance through norms (Castro & Toro, Reference Castro and Toro2004 make a similar argument). People stopped illustrating a way to behave and began insisting on the way to behave. Eventually each society was characterized by a particular set of norms that dictated how individuals should behave (e.g., how they should build a fire, how they should catch a turtle, how they should till the soil) each of which was taught through verbal instruction and imitation. Norms can specify rules of social interaction too, including by detailing how people should respond to norm violation (Fehr & Fischbacher, Reference Fehr and Fischbacher2003). With the advent of norms, hominin social life effectively became transformed from simply living in groups to identifying with the group, abiding by its rules, and privileging in-group members (Sterelny, Reference Sterelny2012). Norms facilitated group coordination and thereby substantially enhanced the society’s capacity for cooperative endeavor. In order to resolve conflicts, or prevent social problems from arising in the future, institutionalizing the norm explicitly, as a ’rule of law’ that all members of the society must abide by, and agreeing sanctions for violators, would sometimes have been necessary (Fehr & Fischbacher, Reference Fehr and Fischbacher2003).

From that point onwards, our ancestors lived in a society structured by cooperatively created and enforced conventions and norms for how to behave, many of which evolved into rule-governed social institutions (Fehr & Fischbacher, Reference Fehr and Fischbacher2003; Tomasello Reference Tomasello, Gelfand, Chui and Hong2010). These norms are far from self-apparent, and young members of society must typically be taught both the nature of the norms, the need to conform to them, and the consequences of not doing so. This much is clear in contemporary human populations where, say, how a cheque or bank transfer works, when, how and why citizens should pay their taxes, or the rules of driving on the roads, are not transparent. All human societies possess such norms and laws, which children generally learn reliably largely because adults actively instruct or teach them, or else devise organized learning environments designed to facilitate learning (Sterelny, Reference Sterelny2012). Human cooperation extends far beyond individuals helping their kin or responding reciprocally to those that help them. Large scale human cooperation is built upon these socially learned and transmitted norms: not just norms specifying how to behave but also norms for rewarding good and punishing bad behavior, known as ‘strong reciprocity’ (Fehr & Fischbacher, Reference Fehr and Fischbacher2003; Fehr & Gachter, Reference Fehr and Gachter2002).

Human social life is far more cooperatively structured than that of any other primate (Tomasello, Reference Tomasello, Gelfand, Chui and Hong2010), largely as a consequence of the norms that thread and stabilize human society. Cooperative enterprises commonly require coordinating the actions of many individuals. Coordinated action amongst pairs or groups of contemporary humans typically involves shared intentionality and goals, joint attention and perspective taking, and joint commitment (Tomasello, Reference Tomasello1999; Reference Tomasello2008; Reference Tomasello, Gelfand, Chui and Hong2010). Here again, teaching is relevant. Teaching another individual how to prepare food, build a fire, or make a tool, requires both joint attention and joint commitment, as well as shared intentions and goals. Effective teaching would also benefit from the tutor taking the perspective of the pupil. The cognitive abilities necessary for coordinating action may initially have evolved through teaching, and subsequently been applied to facilitate large-scale cooperative enterprises. In this manner, language, teaching and conformity have become central to human behavior, in a way that they are not for other animals.

Complex coordinated action amongst multiple individuals is very difficult without social learning, language and teaching (Sterelny, Reference Sterelny2012 ), as it requires some means of coordinating the behavior of the collective. However, through our language and teaching, and through inadvertently constructing learning environments for others, humans can solve this coordination problem, by specifying distinct roles for individuals and training them in how to carry them out (Sterelny, Reference Sterelny2012 ). Indeed, experimental studies have demonstrated that language is an important mechanism through which humans resolve coordination tasks (Brosnan, Wilson, & Beran, Reference Brosnan, Wilson and Beran2012).

Teaching supports mutualism, reciprocity and group selection

There are further grounds for thinking that the uniquely human capacity for cultural learning, teaching and language substantially increased the scope of cooperation in our species (Boyd & Richerson, Reference Boyd and Richerson1985; Fehr & Fischbacher, Reference Fehr and Fischbacher2003; Nowak & Highfield, Reference Nowak and Highfield2011; Richerson & Boyd, Reference Richerson and Boyd2005). Teaching may have originally evolved as cooperation amongst close kin, but with language, teaching could be extended to support other established cooperative processes, such as mutualistic exchanges, indirect reciprocity, and group selection (Nowak & Highfield, Reference Nowak and Highfield2011).

Chimpanzees, orangutans, macaques and capuchins all exhibit population-level differences in their behavioral repertoires but, migration and dispersal aside, there is no evidence of exchange of valued resources between communities. However, amongst those hominin ancestors capable of nascent language, such population-level diversity in material culture would have created the opportunity for the trade in extracted and constructed resources. Evolution of the kind of trade or barter commonly observed in humans, for instance, swapping a tool for food, is challenging to comprehend, as both parties value both of the commodities but, as the commodities are different, the exchange currency requires negotiation. This form of mutualism appears to be rare or absent amongst other animals, which is hardly surprising, as it seemingly requires some capacity to agree a rate of exchange, something that would be very difficult without at least proto-language, or through the flexible use of shared gesture. With the evolution of language, trade becomes a possibility (Ridley, Reference Ridley2011), whilst with trade comes negotiation, and selection for still more developed communication. Particularly in environments that vary from one location to the next, culturally transmitted population-specific diversity amongst linguistically capable hominins creates the opportunity for the mutualistic exchange of goods.

I suspect that the advent of teaching through language was a game changer for our species, by hugely enhancing the scale and mechanisms of cooperation open to us. For instance, that individuals will tend to help those who help them in return (‘reciprocal altruism’) is well-established (Trivers, Reference Trivers1971), but whether individuals will tend to help those who help others (Alexander, Reference Alexander1987), and how prevalent this phenomenon (known as ‘indirect reciprocity’) is in nature, remains far more contentious. Theoretical models have demonstrated that indirect reciprocity can lead to cooperation, and explain why it might pay individuals to develop a reputation for being cooperative (Nowak & Sigmund, Reference Nowak and Sigmund1998) However: “language is intimately linked with cooperation. For the mechanism of indirect reciprocity to work efficiently it needs gossip, from names to deeds and times and places, too” (Nowak & Highfield, Reference Nowak and Highfield2011). In addition, linguistically taught social norms allow humans to institutionalize the punishment of non-cooperative individuals, for instance, through policing or socially sanctioned retaliation, which theory and experimentation shows is a more effective means of preserving cooperation than individual-level punishment (Fehr & Fischbacher, Reference Fehr and Fischbacher2003; Fehr & Gachter, Reference Fehr and Gachter2002).

Inter-population cultural diversity sets a premium on recognizing and preferentially learning from the members of one’s own group who have useful local knowledge, rather than from outsiders who come from other groups. Theoretical analyses suggest that conforming to the local traditions is favored in such circumstances, with several important consequences, including the evolution of ‘ethnic markers’ that symbolize group membership, increased cooperation within groups, and the potential for greater conflict between groups (Boyd & Richerson, Reference Boyd and Richerson1985; Henrich & Boyd, Reference Henrich and Boyd1998; Richerson & Boyd, Reference Richerson and Boyd2005). Languages, or dialects, can function effectively as ethnic markers, promoting local learning and other parochial tendencies (Kinzler, Shutts, DeJesus, & Spelke, Reference Kinzler, Shutts, DeJesus and Spelke2009). In turn, imitation, teaching, languages, and local conventions all act to ensure that local differences in behavior between groups are maintained in the face of the dispersal of individuals between them. This allows an unusually stable form of group selection to arise, known as ’cultural group selection’ (Richerson & Boyd, Reference Richerson and Boyd2005; Richerson et al., Reference Richerson, Baldini, Bell, Demps, Frost, Hillis and Zefferman2014).

Anthropologists Rob Boyd and Peter Richerson first brought to prominence the hypothesis that group selection works at the cultural level, through the selection of group-level cultural traits (Boyd & Richerson, Reference Boyd and Richerson1985). Those groups that possessed more effective or efficient traditions, norms and institutions fared better in competition with other groups. For instance, societies with an organized army are more likely to win conflicts than those without, city-states with division of labor and occupational specializations would tend to out-compete those without these innovations, agricultural communities who have devised irrigation systems would flourish more readily than those in want of them, and people with religious doctrines that stabilize within-group cooperative activities will thrive at the expense of those with no gods to help ensure compliance. The net result is the spread of the concepts, methods and technologies of an army, of division of labor, of irrigation, of religious doctrines, and many other cooperative endeavors.

In such cases, I envisage that natural selection will have operated on groups of individuals, rather than the more conventional selection on individuals. A researcher committed to individual-level selection might reason that, if individuals in agricultural societies end up having more offspring than those in non-agricultural societies then, provided offspring tend to adopt the means of subsistence of their parents, agriculture will increase in frequency. However, such reasoning is overly simplistic. What it neglects is the recognition that most of the fitness benefits associated with agriculture derive from group-level activities. A single farmer scratching a living alone would not typically produce more food or more offspring than a hunter-gatherer. Only when organized into groups that engage in collective enterprises to produce resources that benefit the community (‘public goods’) does agriculture start to become highly productive. As Boyd and Richerson have emphasized, several hundred people are required to construct a decent irrigation system, a corral suitable for catching antelope or horses, or a fish weir built from stone, nets or wooden fencing. Burning the land, sowing the seeds, harvesting the crops have all traditionally been activities in which entire communities engaged. Such activities are infeasible for an individual farmer, but a group of agriculturalists working together could yield substantial dividends, and groups that cooperate in this manner generally outcompete those that do not. The end result is the propagation of cooperative practices.

Boyd and Richerson place emphasis on high-fidelity social learning, conformist transmission by which individuals adopt the behavior of the majority, and norms and institutions that regulate social behavior (Tomasello, Reference Tomasello1999), including the institutionalized, or socially sanctioned, punishment of non-cooperators (Fehr & Fischbacher, Reference Fehr and Fischbacher2003; Fehr & Gachter, Reference Fehr and Gachter2002). The significance of conformist transmission is that it minimizes behavioral differences within groups, while maintaining differences between groups. Moreover, as the payoff to any behavioral strategy depends on the local frequency of its use, then even subpopulations in identical environments may end up performing quite different behavior (Cooper, Reference Cooper1999). In other words, cultural processes generate plenty of variation between human groups for natural selection to act upon. Extensive data now demonstrate that the differences between human societies result far more from cultural rather than genetic variation (Bell, Richerson, & McElreath, Reference Bell, Richerson and McElreath2009).

Several factors make Boyd and Richerson’s cultural group selection mechanism highly plausible. First, in cultural inheritance, unlike genetic inheritance, a descendant can learn from individuals other than their biological parents, allowing conformity to the dominant local behavior, and preserving cultural differences between groups. Second, because a threatened or defeated people may switch to the traits of a new conquering culture, either voluntarily or under duress, unlike gene flow in genetic group selection, migration will not weaken the cultural differences between groups. Thus the movement of people between groups does not typically greatly erode group-level variation. Third, symbolic group marker systems, such as rituals, dances, songs, languages, dress and flags, make it considerably easier for cultures to maintain their identities, and to resist imported cultural traits from immigrants, than it is for local gene pools to maintain their identity by resisting gene flow. Fourth, institutionalized punishment (e.g., by a police force) or socially sanctioned retaliation (e.g., the beating up of deserters during warfare) can stabilize cooperative norms within societies, as both data and theory attest (Boyd & Richerson, Reference Boyd and Richerson1992; Fehr & Fischbacher, Reference Fehr and Fischbacher2003; Fehr & Gachter, Reference Fehr and Gachter2002; Henrich, Reference Henrich2004b; Richerson et al., Reference Richerson, Baldini, Bell, Demps, Frost, Hillis and Zefferman2014). Collectively, this leaves cultural group selection substantially more likely to be operational than genetic group selection, and indeed, the former now commands extensive empirical support (Richerson et al., Reference Richerson, Baldini, Bell, Demps, Frost, Hillis and Zefferman2014).

Cultural processes, including cultural group selection, can feed back through a gene-culture co-evolutionary dynamic to impact on genetic evolution, and fashion our evolved cognition. This interaction is thought to favor evolved psychological predispositions for cultural life, known as ‘norm psychology’ (Chudek & Henrich, Reference Chudek and Henrich2011). Norm psychology refers to “a suite of psychological adaptations for inferring, encoding in memory, adhering to, enforcing and redressing violations of the shared behavioral standards of one’s community” (Chudek & Henrich, Reference Chudek and Henrich2011). Considerable theoretical evidence supports the suggestion that once a species becomes heavily reliant on social learning and culture, it will probably evolve a specialized norm psychology (Chudek & Henrich, Reference Chudek and Henrich2011; Henrich, Reference Henrich2015). Theoretical analyses suggest that humans should be particularly adept at recognizing, representing and adopting the local norms of their society, as well as to notice, condemn and punish violations of those norms (Chudek & Henrich, Reference Chudek and Henrich2011; Fehr & Fischbacher, Reference Fehr and Fischbacher2003). For instance, moral norms could plausibly have generated natural selection acting on human genes to favor cooperative tendencies. ‘Docile’ individuals who are more inclined to conform to norms would find it easier to enter larger norm-bound societies, and to abide by the rules, than individuals lacking this tendency (Richerson & Boyd, Reference Richerson, Boyd, Eibl-Eibesfeldt and Salter1998; Richerson et al., Reference Richerson, Baldini, Bell, Demps, Frost, Hillis and Zefferman2014). A similar mechanism could have favored a tendency of individuals to feel shame or guilt when they violate a social norm (Richerson & Boyd, Reference Richerson, Boyd, Eibl-Eibesfeldt and Salter1998; Richerson & Henrich, Reference Richerson and Henrich2012). While such arguments are speculative, the fact that we would struggle to imagine any other primate that could live in such a norm-governed cooperative manner, combined with the observation that artificial selection in many domesticated animals has favored docility, suggests that selection for such tendencies in humans is highly credible.

Culturing the mind: the evolution of a norm psychology

In addition, the extensive human history of coordinated group behavior and the solving of collective action problems through social learning, teaching and language, have seemingly also fed back to shape human psychology in ways that leave us uniquely able to understand and share the goals and intentions of others in collaborative activities (Tomasello, Reference Tomasello, Gelfand, Chui and Hong2010). We humans appear unusually inclined and able to share experiences with others, via joint attention, cooperative communication, and, of course, teaching (Tomasello, Reference Tomasello1999; Reference Tomasello, Gelfand, Chui and Hong2010). Humans have not just evolved advanced levels of individual cognition, but also extensive skills and motivations for shared cognition. The typical pattern of social foraging among other primates is strong competition for food, low tolerance for food sharing, and almost no food offering at all (e.g., Melis et al., 2006). Our ancestors somehow broke away from this pattern to become cooperative foragers (Sterelny, Reference Sterelny2012). I suspect that selection for efficient and accurate information transmission led to changes in human temperament that left us more socially tolerant (van Schaik & Burkardt, Reference van Schaik and Burkart2011). Social tolerance may also have been favored by cultural group selection, or by other gene-culture co-evolutionary processes.

Gene-culture co-evolution could equally be implicated in the evolution of the enhanced human capacity for imitation, as well as the social bonding that imitation generates, and the activities of caretakers that elicit childhood imitation. For an adult to be imitated by a child may be appealing or advantageous for a number of reasons. Being imitated may be flattering to the imitated party, to the extent that it implies that the imitator has noticed them, chosen them, or values their choices and actions. Second, the imitated individual may wish to encourage the learning of life skills by the child, either because they inherently want the child to develop and mature, or because they want to be relieved of their child caring responsibilities as soon as possible. Third, by engaging in similar activities, children who imitate may be less disruptive, or even helpful, to adult work than children who do not (e.g., children helping with foraging activities). That might explain why parents and helpers commonly encourage imitation in the children that they look after, often showering them with praise and positive reinforcement, and sometimes even imitating the child’s actions and sounds, which theory and data suggests also strengthens imitative competence (Laland & Bateson, Reference Laland and Bateson2001; Pawlby, Reference Pawlby and Scaffer1977). In turn, this encouragement should elicit further imitation from the child. Natural selection could act on this relationship, favoring a tendency to respond positively to, and encourage, being imitated by a child, and a corresponding tendency for infants to imitate adult caregivers spontaneously, and to respond to encouragement with further imitation. The positive emotions experienced by both caregiver and children following imitation, and the enhanced social relationship that results, may be nature’s way of encouraging imitation, to the benefit of both parties.

Infant-directed speech is perhaps a special case of this general process. Language learning is one of many tasks that a child has to learn, and natural selection may have favored the tendency to produce and respond to infant-directed speech because it accelerates language learning (although these phenomena could also have arisen through a cultural evolutionary process). Even everyday phenomena such as smiling and frowning may have been coopted to become part of our norm psychology, as cheap-to-produce but nonetheless highly effective signals of approval or disapproval, which can be easily deployed to teach others what they should or shouldn’t do.

Gene-culture co-evolution may also explain the existence of a surprising relationship between imitation and cooperation. Like other animals, people, often inadvertently, copy each other’s postures, mannerisms and facial expressions. This form of social learning is known variously as ’simple imitation’ (Heyes, Reference Heyes, Calcott, Joyce and Sterelny2012), ’response facilitation’ (Byrne, Reference Byrne, Slater and Halliday1994; Hoppitt & Laland, Reference Hoppitt and Laland2008), ’mimicry’ (van Baaren, Janssen, Chartrand, & Dijksterhuis, Reference van Baaren, Janssen, Chartrand and Dijksterhuis2009), or ’the chameleon effect’ (Chartrand & van Baaren, Reference Chartrand and van Baaren2009). While experiments have established that such copying allows animals to acquire valuable life skills, in humans it also enhances social interaction. Experimental investigations have established that simple imitation is causally related to the emergence of cooperative attitudes, and that the relationship between imitation and cooperation is bidirectional: being imitated makes individuals more cooperative, whilst being cooperative makes one more likely to imitate others (Chartrand & van Baaren Reference Chartrand and van Baaren2009; Heyes, Reference Heyes, Calcott, Joyce and Sterelny2012; van Baaren, Holland, Kawakami, & van Knippenberg, 2004). Experiments show that imitated humans like the imitator more (Chartrand & Bargh, Reference Chartrand and Bargh1999), find them more persuasive (van Swol, Reference van Swol2003), and describe their time together as more enjoyable (Tanner, Ferraro, Chartrand, Bettman, & van Baaren, Reference Tanner, Ferraro, Chartrand, Bettman and van Baaren2008), than do individuals not imitated. Children as young as eighteen months will rush to help adults, for instance, by picking up dropped items, more readily when the adult has imitated the child, compared to when no such imitation takes place (Carpenter, Uebel, & Tomasello, Reference Carpenter, Uebel and Tomasello2013). Adults too are more willing to help others with simple tasks, and even donate more money to charity, after being imitated (van Baaren et al., Reference van Baaren, Holland, Kawakami and van Knippenberg2004).

Moreover, the relationship between imitation and cooperation is seemingly bidirectional. People imitate other people that they like more than those they don’t like, and show a preference for imitating members of their in-group over members of an out-group (Likowski et al., Reference Likowski, Calcott, Joyce and Sterelny2012; Stel et al., Reference Stel, Blascovich, McCall, Mastop, Van Baaren and Vonk2010), including for religious and ethnic groups (Heyes, Reference Heyes, Calcott, Joyce and Sterelny2012; Yabar, Johnston, Miles, & Peace, Reference Yabar, Johnston, Miles and Peace2006). However, experiments show that being imitated by a member of a different ethnic group makes the individual being imitated like the imitator less, rather than more (Likowski et al., Reference Likowski, Calcott, Joyce and Sterelny2012).

Heyes (Reference Heyes, Calcott, Joyce and Sterelny2012) has argued that the bidirectional causal relationship between imitation and cooperation may function to maintain cooperation, collective action and information sharing between members of a social group, via a ’virtuous circle’ of subconscious imitation and pro-social attitudes. The fact that this virtuous circle functions to maintain group boundaries is consistent with these tendencies evolving through a cultural group selection mechanism. Like dialects, local physical mannerisms can spread through imitation to act as ethnic markers that subconsciously symbolize group membership. A tendency to be well-disposed towards individuals that behave like you, including exhibiting your mannerisms, may have been favored as an aspect of our norm psychology because it helped promote cooperation amongst the members of a society. Conversely, mathematical models have found that in variable environments it pays to copy locals, as they are more likely to know the locally optimal behavior (Boyd & Richerson, Reference Boyd and Richerson1985), so a tendency to imitate cooperative individuals may have been favored because such individuals are more likely to be locals. A third possibility is that these tendencies may be learned and socially transmitted.

Cultural group selection may also have favored social practices that foster the development of enhanced imitative capabilities (Heyes, Reference Heyes, Calcott, Joyce and Sterelny2012). Many societies possess traditions of dancing in synchrony, and train their military through extensive synchronous marching and fighting drills. Such groups may have been more successful than other groups in part because this synchronous activity trained up individuals’ neural circuitry for imitative proficiency, allowing them to connect the perception of others performing the action to their own performance (Heyes, Reference Heyes, Hurley and Chater2005; Laland & Bateson, Reference Laland and Bateson2001), thereby promoting within-group bonding (Heyes, Reference Heyes, Calcott, Joyce and Sterelny2012; Wen, Herrman, & Legare, Reference Wen, Herrman and Legare2016). Synchronous action that triggers endorphin release (e.g., a group of individuals that exercise together) may lead to individuals associating synchrony with positive reward, resulting in synchrony itself becoming rewarding through secondary conditioning. Alternatively, if rewards are received at the end of synchronous action, such as hunting together, again a learned association may arise. If synchrony is rewarding, then social behavior that promotes synchrony will be more likely to arise. The extensive use of rhythm (e.g., drumming) and music as means of helping to coordinate the actions of large numbers of individuals and promote social bonding could have been favored in this context (Tarr, Launay, & Dunbar, Reference Tarr, Launay and Dunbar2014). Groups of soldiers that sing or chant when running can run further, faster, with less pain, and bond with each other in the process.

Psychological adaptations for cultural life

Elsewhere, I suggest that selection for more accurate and efficient forms of social learning might have generated selection for enhanced imitative capabilities, as well as other aspects of cognition (Laland, Reference Laland2017). Enhanced imitative capabilities might, for instance, be underpinned by dedicated structures or networks in the human brain that allow us to solve the correspondence problem, or at least might confer the neural plasticity to be able to solve this problem with relevant experience. I believe that our potent capacity for imitation is itself an adaptation to cultural life.

This issue remains contentious, however Heyes (Reference Heyes, Calcott, Joyce and Sterelny2012), for instance, believes that the human capacity for imitation relies on an ancient associative learning capability, and that both the extent of our reliance on imitation, and our imitative proficiency, are socially constructed. I agree that humans have constructed a world, complete with mirrors, and rich with synchronous activities, that is unusually replete with opportunities to develop imitative competences through experience: Patrick Bateson and I made this argument some years ago (Laland & Bateson, Reference Laland and Bateson2001). Experimental evidence demonstrates that imitative tendencies can be increased through positive reinforcement: for instance, when infants imitate parents, the latter typically respond with smiles and encouraging remarks (Pawlby, Reference Pawlby and Scaffer1977). However, I do not believe that other animals would become as competent at imitating as humans if given the same prior experience: indeed, the teaching apes to talk experiments more or less demonstrate this. Heyes (Reference Heyes, Calcott, Joyce and Sterelny2012) asks ‘What’s social about social learning?’ and after presenting evidence that social and asocial learning are underpinned by the same mechanisms, concludes that the term ‘social learning’ is misleading. In my view such reasoning (which is only tenable because it disregards all social learning operating through language or teaching) puts the cart before the horse. There has been extensive natural selection acting on the human brain in the period since humans and chimpanzees shared a common ancestor, including evidence that our learning capabilities have been massively up-regulated (Laland, Odling-Smee, & Myles, Reference Laland, Odling-Smee and Myles2010). Both neural (Marino, Reference Marino2006; Streidter, Reference Striedter2005) and genetic (Laland et al., Reference Laland, Odling-Smee and Myles2010) evidence suggest that humans possess elevated levels of plasticity that allow them to form cross-modal neural connections between sensory inputs and motor outputs, and thereby facilitate imitation and emulation, relative to other primates. As one would expect if humans have evolved extended periods of juvenile dependency to promote the transfer of knowledge across generations, the period of synaptic plasticity characteristic of early brain development has been extended in humans (Somel, Rohlfs, & Liu, Reference Somel, Rohlfs and Liu2014). Even our basic and ancient learning capabilities, including our capability for classical conditioning, operant conditioning, and reversal learning, have been substantially upgraded, most probably through selection for enhanced social learning (Laland, Reference Laland2017). This enhancement in general learning and plasticity is likely to play critical roles in human cognitive development. In sum, almost all human learning is social guided and set in a social context, and that is also likely to have been the case for our ancestors for several million years. At least with respect to humans, then, we might more reasonably ask ‘What’s asocial about asocial learning?’ It would seem more appropriate to regard the enhanced human capacity for asocial learning as a side effect of selection for proficient copying, rather than the other way around (van Schaik & Burkart, Reference van Schaik and Burkart2011, make a similar argument).

Showing that a character is an adaptation has proved surprisingly difficult for evolutionary biologists, and hence demonstrating that certain cognitive traits possessed by humans are adaptations to promote social learning is no trivial task. Indeed, I consider the issue of what precisely are human social learning adaptations to be one of the great, unresolved questions in the field. Nonetheless, there are a sufficient number of strong candidates to leave me confident that humans will eventually be shown to possess cognitive adaptations for cultural learning.

The human generalized capacity for teaching, including the motivation to teach and be taught, and the ability to comprehend the state of knowledge of the pupil, is one such candidate (Fogarty et al., Reference Fogarty, Strimling and Laland2011). If I am correct about the original function of language to promote teaching, then language is another (Laland, Reference Laland2017). The tendency to produce, and to attend to, infant-directed speech are further traits that may have evolved to promote social transmission, as are other forms of pedagogical cueing (Csibra, Reference Csibra2010; Gergely & Csibra, Reference Gergely and Csibra2005; Gergely, Egyed, & Király, Reference Gergely, Egyed and Király2007). The extraordinary social motivation to imitate, that anyone with children will recognize as powerful and pervasive, and the social bonding between individuals that this generates, constitutes another strong case (Tennie, Call, & Tomasello, Reference Tennie, Call and Tomasello2009). The tendency of young children to attend to the gaze of others, and the motivation to share experience with others, via joint attention is a further compelling candidate (Tomasello, Reference Tomasello1999; Reference Tomasello, Gelfand, Chui and Hong2010)^. Even the whites of our eyes may have evolved to make it easier for us to follow another individual’s gaze direction in close-quarter communicative interactions (Tomasello, Hare, Lehmann, & Call, Reference Tomasello, Hare, Lehmann and Call2007). The extraordinary human tendency to conform to the majority (Morgan, Rendell, Ehn, Hoppitt, & Laland, Reference Morgan, Rendell, Ehn, Hoppitt and Laland2012) is another strong candidate for a social learning adaptation. Cultural evolution models, but not associative learning theory, can explain why humans should be more likely to copy an action performed by three individuals, once each, than an action performed by one individual three times (Haun, Rekers, & Tomasello, Reference Haun, Rekers and Tomasello2012). The human capacities for theory of mind and perspective taking, and abilities to read the intentions of others, are surely also part of this story (Call, Hare, Carpenter, & Tomasello, Reference Call, Hare, Carpenter and Tomasello2004; Call & Tomasello, Reference Call and Tomasello1998; Reference Call and Tomasello2008).

While I anticipate that multiple psychological adaptations for social learning may eventually be uncovered in our species, I expect the unlearned roots of such cognition to be subtle. Social learning adaptations are likely to be expressed as complex products of development that build upon weak evolved motivational, perceptual or cognitive biases through domain-general learning responding sensitively to a culturally constructed, symbolically encoded environment (Bolhuis et al., 2011; see Carey (2009) for illustrations of how such cognitive adaptations emerge).

Large-scale cooperation is only possible in our species because of our uniquely potent capacities for social learning, imitation and teaching, combined with the co-evolutionary feedbacks that these capabilities have generated on the human mind. Human cognition is entirely different from that observed in any other animal, or that could have evolved through conventional selection on genes alone, and is uniquely adapted to cultural life.