Vaesen presents a list of social and cognitive factors that he believes, in concert, explain the differences between human and chimpanzee tool use. We believe that Vaesen is too quick to reject explanations based on a smaller number of key traits; in particular, the traits outlined in the cultural intelligence hypothesis.

Cultural intelligence (CI) can come about in two (potentially complementary) ways. First, culture can enhance intelligence during an individual's lifetime (“ontogenetic” CI; Herrmann et al. Reference Herrmann, Call, Hernández-Lloreda, Hare and Tomasello2007; Tomasello Reference Tomasello1999). The ontogenetic CI hypothesis postulates that growing up in a culturally rich environment enables children to develop cognitive skills they would not otherwise have done (Moll & Tomasello Reference Moll and Tomasello2007). According to this perspective, human-unique forms of social learning and teaching are responsible for qualitative changes in cognition – including changes in the ways in which we use tools. Therefore, at least some of the factors that Vaesen identifies as causes of human tool use are, in fact, effects of growing up in rich cultural environments.

Second, culture can play a role in the evolution of cognition across generations (“phylogenetic” CI; see also van Schaik & Pradhan Reference van Schaik and Pradhan2003). Much less is known about this form of cultural intelligence. However, van Schaik & Pradhan (Reference van Schaik and Pradhan2003) modeled the co-evolution of culture and innovations and found that “high intelligence will often be a by-product of selection on abilities for socially biased learning.” In other words, selection pressure for better social learning leads indirectly to the evolution of individual learning (and not vice versa).

In defense of his claims, Vaesen argues that as culture became more complex, greater intelligence was needed in order to deal with increasingly sophisticated cultural artifacts. However, this neglects the possibility that culture positively impacts on intelligence – as posed by the two CI hypotheses. In support of this perspective, Enquist et al. (Reference Enquist, Ghirlanda, Jarrick and Wachtmeister2008) modeled cultural accumulation and showed that culture would level off unless faithful forms of social transmission impact on innovation levels. As culture has increased exponentially in modern humans, the most plausible view is that culture and intelligence form a feed-forward loop.

So far we have suggested that cumulative culture explains human intelligence in general, and sophisticated forms of tool use in particular. What then explains the existence of cumulative culture? We believe that the answer lies in species-unique forms of social learning and teaching.

Vaesen identifies a number of potential differences between social learning in humans and in chimpanzees. Although these differences may be accurate, we believe that the most basic differences between human and chimpanzee social learning lie elsewhere. Below we outline our alternate account of social learning in chimpanzees and compare it with the case of human children.

After critically reviewing the available evidence on social learning in chimpanzees, Tennie et al. (Reference Tennie, Call and Tomasello2009) argued that chimpanzee cultures are best described as serial reinventions across multiple generations. Social learning can still play some role in explaining the distribution of behaviors over time and space (e.g., Whiten et al. Reference Whiten, Goodall, McGrew, Nishida, Reynolds, Sugiyama, Tutin, Wrangham and Boesch1999), as it can increase the chance of reinvention. Social learning could even be responsible for cases in which the best target for a particular behavior is found and maintained over time (e.g., the whereabouts of the most bountiful feeding place). But the form that chimpanzee behaviors (including these “cultures”) take is most strongly determined by biological and ecological factors. This account is supported by evidence suggesting that if chimpanzees copy behavioral forms (i.e., imitate) in the absence of training, then they do so rarely and/or not very precisely (Tennie et al. Reference Tennie, Call and Tomasello2009; Whiten et al. Reference Whiten, McGuigan, Marshall-Pescini and Hopper2009). In addition to this, teaching is virtually absent in chimpanzees (although see Boesch Reference Boesch1991). Without teaching, and with imitation severely limited, chimpanzees lack the transmission fidelity necessary to sustain true cumulative culture (where the form of behavior is transmitted). In turn, ontogenetic CI in chimpanzees (at least in the wild) is probably severely limited.

In contrast to social learning in chimpanzees, human social learning is typified by faithful transmission. Human children often imitate the specific actions of a model. Indeed, they do so even when it results in less efficient performance on their part (Nagell et al. Reference Nagell, Olguin and Tomasello1993) and when they have been explicitly instructed not to (Lyons et al. Reference Lyons, Young and Keil2007). This faithful transmission is at least partially the result of the social motivations and pressure underlying imitation (Over & Carpenter Reference Over and Carpenter2011). In contrast to chimpanzees, human children experience a strong drive to be like their group members (Nielsen Reference Nielsen2009; Nielsen et al. Reference Nielsen, Simcock and Jenkins2008; Over & Carpenter Reference Over and Carpenter2009). This motivation can lead children to produce faithful copies of modeled acts even when it appears irrational to do so. Furthermore, humans often experience social pressure to imitate in particular ways. One form of social pressure is teaching. Gergely and Csibra (Reference Gergely, Csibra, Enfield and Levinson2006) have shown that even infants are sensitive to teaching cues and that they copy actions more precisely when teaching cues are present. Social pressure to imitate can also come from the group in general. Haun and Tomasello (Reference Haun and Tomasello2011) have recently demonstrated that preschool children conform to the behavior of their peers and that they do so more in public than in private. Evidence from Rakoczy et al. (Reference Rakoczy, Warneken and Tomasello2008) suggests that not only do children experience social pressure; they exert it on those around them by enforcing social norms.

Thus, in contrast to Vaesen, we emphasize that a small number of key factors (e.g., imitation and teaching) render human culture a more social enterprise than is chimpanzee culture. Over time, these factors have played a causal role in producing qualitative changes in human cognition, including in the ways we use tools.