Like Me: A Homophily-Based Account of Human Culture
In this chapter, we introduce a homophilic account of human social structure and cultural transmission. According to this account, a tendency to favour similar others (homophily) has been a key driving force in creating unique human forms of culture and thus evoked the striking differences we observe between human groups. We begin by presenting evidence that, from the early stages of development, humans have shown a strong tendency to interact with, and learn from, individuals who are similar to themselves. Following this, we propose that the homophilic preferences of the group in general has created a feedback loop that ensures that children engage in high-fidelity copying of the group’s behavioural repertoire. This allows children to reap the benefits of others’ homophilic preferences and to therefore maintain their position within the group. In consequence, homophilic preferences have transformed a number of mechanisms that we share with other species, for example emulation and majority-biased transmission, into human unique variants such as social imitation and conformity. Homophilic preferences have furthermore spawned a new tendency to interpret the structure of actions as social signals: norm-psychology. The homophily account thus connects previously disparate findings in comparative, developmental, and social psychology and provides a unified account of the importance of the preference for similar others in species-specific human social behaviour.
KeywordsHomophily Social structure Cultural transmission Norm-psychology Conformity
In many ways, the stability of human cross-cultural variation is surprising, since high rates of migration (Hill et al. 2011) and visitation (Chapais 2008) should, over time, reduce differentiation across groups (Yeaman et al. 2011). Assuming a long enough period, any difference between human groups should inevitably fade by means of these processes (Boyd and Richerson 2005, 2009; Henrich and Boyd 1998).
Independent of inter-group migration, there is another parallel migration into any group at any given point in time: newborns. Every new generation of children confronts the group with a number of individuals that do not act according to the group-specific behavioural repertoire (Harris 2012). Thus, in addition to immigrants entering the community with conflicting behaviours and norms, there is also a constant influx of individuals entering the community either without any established behavioural patterns or sometimes even with predispositions that are counter to the local cultural variant of a particular behaviour (e.g. Haun et al. 2006).
How then do children acquire the appropriate group-specific beliefs and behaviours? Previous accounts of cultural transmission have emphasized the role of learning mechanisms such as high-fidelity imitation (Lyons et al. 2007; Whiten et al. 2009) or cognitive abilities such as perspective taking (Tomasello 1999) and sensitivity to ostensive cues (Gergely and Csibra 2006). In contrast to these accounts, we emphasise the importance of more social processes, in particular, homophily (a preference for others we perceive as similar to ourselves). The homophily account is based on two closely related claims. First, children preferentially affiliate with and learn from similar others. Second, and more importantly, the homophilic preferences of the group in general create a feedback loop that ensures that children engage in high-fidelity copying of the group’s behavioural repertoire. This allows them to reap the benefits of others’ homophilic preferences and to therefore maintain their position within the group. This homophily-based account thus unites research on the social functions of imitation (e.g. Carpenter and Call 2009; Over and Carpenter 2012; Nadel 2002; Nielsen 2009; Užgiris 1981) with that on group membership (e.g. Dunham et al. 2011; Kinzler et al. 2007; Turner 1991) and normative behaviour (Kallgren et al. 2000; Rakoczy et al. 2008).
We do not claim that the homophily account provides an exhaustive description of how social motivations influence cultural transmission. Other social motivations and preferences (for example, for prestigious others and competent others) and the interactions between them are also important in explaining humans’ social learning (Laland 2004). We simply wish to highlight that the preference for similar others is one key factor in explaining cultural transmission and that species-specific differences in this tendency might be one factor in explaining the origins of species-typical features of human cultural transmission.
Below, we outline our homophilic account in more detail. We begin by discussing the importance of homophilic assortment from an evolutionary perspective. After that, we review the available evidence that, from the early stages of development, humans have had a strong preference for similar others. We then move on to the main thrust of our argument and present evidence that this preference for similar others has transformed a number of pre-existing cognitive mechanisms, such as emulation learning and majority-biased transmission, into a suite of human-unique traits that includes social imitation, conformity, and a norm-psychology.
6.2 Homophilic Social Preferences from an Evolutionary Perspective
For cooperation to be maintained within a group, it is essential for group members to be able to distinguish cooperators from defectors. In stable, personalized groups, familiarity serves to reduce aggression and to create a tolerant context; the foundation of any cooperative exchange. As groups increase in size, so does the frequency with which individuals have to interact with less and less familiar others. Eventually, the personal interaction history can no longer be relied on to estimate the reliability of a partner.
At some point during human evolution, social networks increased to a size where group members were more and more likely to encounter others that were only vaguely familiar. For instance, even the most mobile extant forager groups live in networks that typically exceed several hundred individuals (Hill et al. 2011; Apicella et al. 2012). Under such conditions, familiarity itself remains important, but is no longer as effective as before. Thus, a proxy measure for familiarity is required that reliably correlates with familiarity. Similarity in aspects of the phenotype (morphology and behaviour) is one such measure. Individuals who grow up within the same community are likely to be similar on a number of dimensions, thus making phenotypic similarity an honest signal of group membership.
We argue that a preference for similar others allowed humans to assort between strangers, identifying in-group members who were not personally known to them. Choosing to interact and cooperate with more similar strangers maximised the chance of successful cooperative interactions because similar individuals were more likely to share relevant behavioural tendencies (McElreath et al. 2003; Cohen 2012). In consequence, humans were able to function within qualitatively different forms of social organisation compared to other primates, thus tapping into the cooperative potential of strangers. Formal models have shown that such a pattern of cultural transmission, in which individuals are disproportionally influenced by those who are similar to themselves, is adaptive, since a homophilic preference causes sub-populations to become culturally isolated. This in turn allows the mean value of locally adaptive traits to converge to the optimum. A transmission strategy based, for example, on success would only adapt much more slowly to a variable habitat (Boyd and Richerson 1987). In other words, “the preference to interact with people with markers like one’s own may be favored by natural selection under plausible conditions” (McElreath et al. 2003, p. 123).
In the next section, we shift our focus to empirical evidence supporting this hypothesis. We centre our discussion on the developmental and comparative data demonstrating that the human preference for similar others is much stronger than that seen in other primate species.
6.3 Like Me? Homophilic Social Preferences from a Comparative Perspective
6.3.1 Homophilic Social Preferences in Non-human Primates
Interpersonal relations in chimpanzee groups are characterised by tolerance of in-group members and hostility towards out-group members (Wrangham 1999; Wilson et al. 2012). Members of other groups detected within the home range are typically killed (with the one exception being migrating females; Kahlenberg et al. 2008). This preference for in-group members over out-group members is almost certainly based on familiarity rather than similarity, as chimpanzees typically encounter all the members of their own group on a fairly regular basis.
A recent study however raises the possibility that some non-human primates also use similarity as a means to assort between others. Paukner et al. (2009) reported that capuchin monkeys who were presented with two human experimenters, one who imitated them and another who just performed monkey-like movements, sat closer to the imitator and exchanged more tokens with him. Hence, a transient increase in behavioural similarity (social mimicry) made capuchins prefer one human to the other.
There are thus some hints that non-human primates utilise similarity in their social judgments (at least to some extent) and, in consequence, that the common ancestor of humans and other primates had rudimentary preferences for similar others. This may have provided the evolutionary starting point from which homophilic social preferences in humans could emerge. As we will see below, however, the evidence for homophilic preferences in humans far exceeds that of any other primate.
6.3.2 Homophilic Social Preferences in Children
In contrast to non-human primates, the evidence that humans assort unfamiliar others based on similarity is quite substantial (e.g. Gruenfeld and Tiedens 2010; Jones et al. 2004; Tajfel et al. 1971). This preference for similar others appears to structure social interactions from early development. For example, 6-month-olds prefer to look at individuals who speak their own versus a different language, and 10-month-olds prefer to accept toys from speakers of their own language (Kinzler et al. 2007). This preference for native language speakers structures social interactions also later in development: 5-year-olds preferentially choose native language speakers over foreign-language speakers or foreign-accented speakers as friends (Kinzler et al. 2009). However, in all the above-mentioned studies with children it is not possible to separate a preference for similar others from a preference for individuals children find easier to understand.
Fawcett and Markson (2010) have provided evidence that young children’s social preferences are, at least at times, based on self-similarity alone. Fawcett and Markson demonstrated that 3-year-old children prefer to play with a puppet who expresses the same food preference as them as opposed to a contrasting preference, and a puppet whose physical appearance matches rather than mismatches their own. Other evidence comes from research on the effects of being imitated. One of the consequences of being imitated is a momentarily increased level of perceived similarity between social partners (Chartrand and Bargh 1999). From early in development, children appear to prefer individuals who imitate them to individuals who engage in independent behaviour. For example, 14-month-old infants look towards and smile more at an experimenter who imitates them than at an experimenter who engages in equally contingent but non-imitative behaviour (Agnetta and Rochat 2004; Asendorpf et al. 1996; Meltzoff 1990). Furthermore, infants and toddlers are more likely to help an experimenter who has imitated them than an experimenter who has engaged in contingent but non-imitative behaviour (Rekers and Haun submitted).
Further evidence for children’s preference for similar others comes from the so-called minimal group paradigm (Tajfel et al. 1971). In this paradigm, individuals are randomly allocated to one of several groups that are only identified by an abstract, seemingly uninformative symbol. In this way, similarity between members of a minimal group is not indicative of any shared behavioural characteristic of the individuals composing the group, but only of shared group identity. Five-year-old children prefer individuals allocated to the same minimal group as them over individuals allocated to a different minimal group. Furthermore, children not only prefer individuals belonging to the same minimal group but also have more positive expectations about in-group members’ behaviour (Dunham et al. 2011).
This preference for similar others seems to occur across cultures (Kinzler et al. 2012; Cohen and Haun 2013). Children’s relative reliance on particular cues, however, varies depending on the particular socio-cultural context. Recent studies comparing children in different townships along the Brazilian Amazon have demonstrated that children’s preferences for certain cues are likely tuned according to locally relevant cue variation. For example, children from accent heterogeneous populations rely more strongly on accent as a similarity cue than children from accent homogeneous populations (Cohen and Haun 2013).
6.3.3 Children Prefer to Learn from Similar Others
Children’s preference for similar others not only indirectly channels their own input by creating interaction bubbles of similar others but also has more immediate implications for children’s social learning. Kinzler et al. (2011) demonstrated that 5-year-old children are more likely to learn the function of a novel object from an individual who speaks with the child’s native accent than from an individual who speaks the same language with a foreign accent. A more recent study claimed that even infants preferentially learn from similar others (Buttelmann et al. 2012). In this study, 14-month-old infants listened to a story told either in their native language or in a foreign language. Children subsequently imitated the actions of the speaker of their native language more closely. Caution must be taken when interpreting this result, however, as the design confounds similarity with other factors such as the relative comprehensibility of the stories. Nevertheless, it raises the possibility that children select their models by similarity already in the second year of life.
Other evidence that children preferentially learn from similar others comes from research on the effects of being imitated. In a recent study, Over et al. (2013) found that 5- to 6-year-old children were more likely to adopt the preferences and novel object labels of an experimenter who had previously imitated their choices than those of an experimenter who had previously made independent decisions.
It appears from the above that the human preference for similar others likely far exceeds that of any other primate. This preference is present early in development and structures children’s learning as well as their social interactions. In the next section, we outline the consequences of this homophilic social preference for the mechanisms underlying cultural transmission.
6.4 Like Me! The Consequences of Homophilic Preferences
If we prefer similar to dissimilar others, it follows that increasing the similarity between self and other can be a useful strategy for directing others’ positive social activities towards the self. We contend that homophilic preferences in humans have interacted with the social learning mechanisms inherited from our common ancestor with the other great apes and transformed them into species-unique forms of copying behaviour which serve to maintain individuals’ position within the group.
In contrast to previous accounts (e.g. Carpenter and Call 2009; Užgiris 1981), the homophilic account does not require children to have the goal of making themselves more similar to their social partners. Although children may, at times, actively seek to be like others (Carpenter 2006; Over and Carpenter 2013), the more typical pattern for children may be to learn through experience that imitation is successful in improving social relations, without any explicit awareness of this connection. In consequence, their only goal within the social situation may be to get along well with others.
In the remainder of this chapter, we discuss evidence that social learning mechanisms we share with other species—emulation and majority-biased transmission—have been transformed by homophilic preferences into a suite of human-unique social learning processes including social imitation, conformity, and a norm-psychology.
6.4.1 Emulation Becomes Imitation
Chimpanzees use a range of social learning strategies, including most prominently emulation (Call et al. 2005; Nagell et al. 1993). In emulation learning, an animal focuses on the outcome that is achieved in the physical world rather than the particular actions that were used to achieve it (Tomasello et al. 1993). If chimpanzees copy the particular actions of their conspecifics (i.e. imitate), they appear to do so infrequently and with relatively low fidelity (Tennie et al. 2009).
Children, in contrast, show a strong tendency to copy actions faithfully. In fact, children’s imitation is sometimes so precise that they even copy actions that are superfluous or disadvantageous to solving the task at hand (Horner and Whiten 2005; Nagell et al. 1993; Nielsen 2006). For example, children from 3 to 5 years of age, who have been trained to identify the causally irrelevant parts of novel action sequences, still reproduce causally irrelevant actions, and they continue to do so even when specifically instructed by the experimenter to copy only necessary actions (Lyons 2009; Lyons et al. 2007). This phenomenon has come to be called overimitation (Lyons et al. 2007; Lyons et al. 2011). It emerges in the 2nd year of life (Nielsen 2006) and becomes increasingly pervasive through the preschool period (McGuigan and Whiten 2009; McGuigan et al. 2007).
The homophilic account presumes that these differences in social learning between chimpanzees and humans have been driven, at least in part, by human homophilic preferences. The increased importance of “how something is done” is owed to the significance of behavioural similarity amongst individuals of a group. Finding a different way to achieve the same ends is no longer functionally equivalent to exactly copying others’ actions, since the former decreases similarity with others while the latter increases it. For humans, imitation could thus serve new social purposes. This added social dimension effectively turned emulation learning into faithful imitation.
In consequence, it is misleading to refer to high-fidelity imitation as “overimitation”, since the term implies that children copy unnecessary parts of action sequences. Under the homophily account, these parts, while being causally irrelevant, still serve an important function for the learner: They produce a high level of similarity between the demonstrator and the learner.
Evidence in favour of the proposal that high-fidelity imitation is used to achieve social goals comes from data suggesting that children increase their tendency to imitate when affiliation is important to them. Over and Carpenter (2009) demonstrated that 5-year-old children who have been given a goal to affiliate (through priming with social exclusion) imitate the actions of a model more closely than children who have been given a neutral prime. Further evidence in favour of this hypothesis comes from work demonstrating that children are more likely to copy the specific actions of a model when that model is in the room and thus able to watch their imitation (Nielsen and Blank 2011). Imitation is also closely associated with social factors in younger children. Nielsen et al. (2008) demonstrated that 2-year-old children are more likely to copy the specific actions of a model who engages in a contingent social interaction with them than those of a model whose behaviour is not contingent on their own.
The tendency to make the self similar to others can also be used more strategically within social settings. That is to say, imitation can serve Machiavellian ends (Over and Carpenter 2012). Research with older children has shown that they are able to use imitation in order to increase their influence over others. For example, Thelen and colleagues demonstrated that 10-year-old children are more likely to copy the specific actions of a peer when they will later need to persuade that peer to do something (Thelen et al. 1980).
6.4.2 Majority-Biased Transmission Becomes Conformity
Homophilic preferences, we argue, have influenced not only how we interact with individual social partners but also how we respond to the group in general. One way in which humans interact with the group as a whole is through consideration of the majority.
If, due to any combination of underlying mechanisms, an individual is more likely to acquire the behaviour displayed by the majority, we refer to it as a majority-biased transmission (Haun et al. 2012). A recent study with chimpanzees showed that naïve individuals copy the behaviour of the majority instead of alternatives, even if those are equally frequent, equally familiar, and equally productive behaviours (Haun et al. 2012).
Thus, chimpanzees follow the majority when they have no prior information available. However, they do not follow a majority if they have to forgo their own behavioural tendencies in order to do so (Haun et al. submitted). We refer to the tendency to forgo personal preferences in favour of copying the majority as conformity (Haun et al. 2013; van Leeuwen and Haun 2013). The authors of a recent study argue that chimpanzees conformed against their own preference, based on the finding that individuals retained their socially acquired strategy even though the alternative yielded more preferred rewards (Hopper et al. 2011). However, because individuals only very rarely experienced the alternative strategy to yield more desirable foods, it remains highly questionable if individuals were, in fact, fully aware of the alternative.
Similar to chimpanzees, human children follow the majority if they have no relevant information available (majority-biased transmission, Haun et al. 2012). However, in contrast to other primates, human children also adjust their behaviour to the majority even when they have an equally effective but individually acquired strategy available already: In a situation in which one child, with high level of performance on a certain task, is confronted with a majority of peers who unanimously give a false response, children often choose to abandon their own judgement and to adjust their behaviour to the majority’s response (Berenda 1950; Corriveau and Harris 2010; Haun and Tomasello 2011; Walker and Andrade 1996). Furthermore, children appear to consider the social consequences of conforming versus dissenting. Haun and Tomasello (2011) varied the privacy of the subjects while giving their response and found lower rates of conformity when preschool children were allowed to keep their response private from the majority. Most strikingly, children adjusted their level of conformity from trial to trial, depending on the privacy of their response, conforming more often when they gave their response in public. The authors concluded that the reduction in conformity in the private condition demonstrated a partial contribution of social motivations for children’s conformity on the public trials. Hence, children, in contrast to other primates, are additionally guided by social motivations when conforming to a majority (Haun and Tomasello 2011).
In the absence of a social function, copying the majority when acquiring a new skill is adaptive on an individual level, but there is no reason to follow the majority in cases where the learner already has a different but equally productive strategy available to them. However, if conformity also serves a social function, then it pays for a learner to forgo their own strategy and adopt that of the majority, since sticking to the former will decrease similarity between the self and the group, while conforming to the latter will increase similarity between the self and the group. According to the homophily account, this added social dimension increased humans’ tendency to conform to the majority, effectively turning majority-biased transmission into conformity.
6.5 The Emergence of Norm-Psychology
Non-human primates, such as chimpanzees, have “rules of conduct” that are reinforced. For example, subordinates tend to display certain gestures when meeting a dominant individual and violations of this behavioural pattern will result in aggression (Goodall 1986). Although the superficial structure of these patterns of behaviour might resemble that of human norms, they differ from norms in important respects (Tomasello 2008). For example, while human norms are often variable across groups, gestures negotiating the relationship between dominant and subordinate individuals in chimpanzees are highly similar across different, unrelated populations, thus suggesting that they are not culturally learned (Tomasello et al. 1997). Furthermore, chimpanzee “rules”, unlike human norms, are not agent neutral. Subordinate chimpanzees failing to submit to the dominant might suffer aggression from the dominant (the affected party), but not from other (unaffected) group members. Chimpanzees do not appear to punish the violations of third parties (Riedl et al. 2012). Humans, on the other hand, punish the transgressions of others even if they do not concern them directly (Henrich et al. 2006). Hence, it does not seem to be the case that chimpanzees collectively intend to do things in a certain way and do not have any normative expectations about their conspecifics’ behaviour, but that their social interactions are better characterized by behavioural regularities and individual and idiosyncratic preferences for certain behaviours.
Human norms are rich in their social interpretation: Norms describe the “right” way to do things, the way things “ought” to be done, the way “we” do things (Bruner 1993). Human children appear to spontaneously detect such norms in many behaviours even in the absence of normative language (Schmidt et al. 2011). After a single confident and intentional demonstration by an adult, children appear to assume that the way in which an action was demonstrated is normative. Following such a demonstration, children will not only follow that norm but also actively enforce it when later observing someone performing the action “incorrectly”, often protesting using normative language about what people ought to do (Rakoczy et al. 2008). Thus, children readily enforce norms on others even if their violation does not impact upon them directly.
We have argued above that the social relevance of similarity amongst individuals gives previously socially neutral behaviours a new social relevance. The “way something can be done” is effectively elevated to the “way we do something”, fitting actions with a social signalling function. This normative dimension to actions that have no intrinsic value (e.g. how to hold a fork) is, we argue, a direct consequence of the relevance of self–other similarity in cooperative groups of increasing size.
Many accounts exist for the species-unique structure of human social behaviour. All of them contain lists of human-specific social abilities and motivations for coordination (Tomasello et al. 2005), social learning (Tennie et al. 2009), teaching (Gergely and Csibra 2006), and norm-psychology (Chudek andHenrich 2011). We have provided an account that unites some of these previously unconnected sets of abilities and motivations. According to our homophily-based account, a preference for similar over dissimilar others underlies important aspects of human-unique social behaviour.
Evidence suggests that, from early development, children prefer to interact with, and learn from, individuals who are similar to themselves. This preference for similar others and the potential advantages reaped by being similar to others, ensures that children engage in high-fidelity copying of the group’s behavioural repertoire. In consequence, seemingly irrelevant parts of actions gain social relevance by serving as a similarity marker. This tendency to interpret the physically irrelevant structure of actions as social signals, we argue, spawned a human-unique form of interpreting the actions of others: norm-psychology.
In summary, we argue that species-specific difference in homophilic preferences might be one key factor in explaining the origins of species-typical features of human cultural transmission. We predict that humans are unique amongst living primates in the extent of their preference for similar others. We also predict that this preference is universal across human cultures, albeit relying on different similarity cues in different populations (Logan and Schmittou 1998; Cohen and Haun 2013). Future studies should further test these predictions from cross-cultural and comparative angles.
We would like to thank Malinda Carpenter, Emma Cohen, Emma Flynn, Katja Liebal, Nadja Richter, Carel van Schaik, Claudio Tennie, Marco Schmidt, Peter Richerson, and an anonymous reviewer for valuable comments on an earlier draft.
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