In the target article, Vaesen notes a remarkable discontinuity between humans and chimps in tool use and cognitive features. Language is suggested to play a merely facilitative role for other cognitive functions. We propose that Vaesen (a) underestimates the role of language in humans' cognitive toolkit and thereby (b) overestimates the proposed cognitive discontinuity between chimps and humans.

Language can be considered, in Clark's words (Reference Clark2008), as a mind-transforming cognitive scaffold. It can productively transform people's cognitive capacities by simplifying their outer world. For instance, the simple act of labeling creates a new constellation of “perceptible objects” and reconfigures the problem space (Clark Reference Clark, Keil and Wilson1998a), thereby increasing people's computational ability enormously. Consider numerical computation as another example. Dehaene and colleagues (Reference Dehaene, Spelke, Pinel, Stanescu and Tviskin1999) proposed that when people use number words to complement more basic biological capacities, people acquire an evolutionary novel ability to deal and think about unlimited exact quantities, hinging crucially on language. Systematic skill improvement attempts, fault detection, and corrections of flaws in people's own planning – to mention only few – are the result of the interaction of biological brains with linguaform resources that together allow “thinking about thinking” (Bermudez Reference Bermudez2003; Clark Reference Clark, Carruthers and Boucher1998b; Reference Clark2008). As such, language opens up new computational opportunities, enabling humans to solve complex problems. This may be the case for some (if not most) of the cognitive tools that Vaesen points out in his target article.

Furthermore, we agree that one cannot easily determine the evolution of language (cf. Richerson & Boyd Reference Richerson and Boyd2005). Yet, it is undisputed, also by Vaesen, that language has been particularly useful for participating in culture, in particular in keeping track of complex relational systems (i.e., gossip). However, relatively simple forms of communication are not unique to humans; the most primary vocalizations even seem to be present in primates, which often participate in relatively simple relational systems (Dunbar Reference Dunbar1997). As such, language seems to have developed primarily for purposes directly related to social interactions, becoming more important once people began living in larger groups. Language has since become immensely important for other cognitive tools. Clark even suggested that the “recent intellectual explosion in evolutionary time is due as much to linguistic-enabled extensions of cognition as to any independent development in our inner cognitive recourses” (Clark Reference Clark2008, p. 232).

This point is further exemplified by recent work in (social) psychology. As an example of two of the cognitive tools Vaesen put forth – executive functioning and body plasticity – we know that both chimps and humans show relatively simple and automatic affiliative behaviors in response to an angered interaction partner (Häfner & IJzerman Reference Häfner and IJzerman2011; Preuschoft & Van Hooff Reference Preuschoft, Van Hooff, Segerstrale and Molnàr1997). Humans, however, seem to have the unique capacity to control the self to accommodate for the other in committed relationships (Rusbult et al. Reference Rusbult, Verette, Whitney, Slovik and Lipkus1991). One could wonder to what extent similar behaviors may occur in other species that display monogamous pair bonding.

Yet, the simple fact that humans possess advanced abilities to postpone immediate self-interest (i.e., self control) in relation to negative emotions like anger (and their facial expressions) is not surprising, as language has been shown to closely rely on modality specific representations that guide and help people's cognition (e.g., Pulvermüller Reference Pulvermüller2005; Zwaan & Taylor Reference Zwaan and Taylor2006). Verbs (indicative of action; compared with adjectives) related to smiling or frowning induce greater activation of zygomaticus or corrugator muscles (Foroni & Semin Reference Foroni and Semin2009). In addition, physically warm (as compared with cold) conditions induce people to use more relational language (verbs; IJzerman & Semin Reference IJzerman and Semin2009). One might logically propose that linguistic features play a vital part in actions and thoughts above and beyond “merely” “extending the body.” Research suggests it can. Linguistic features permit to represent close and near “future” at different abstraction levels, allowing people to coordinate and plan future joint and individual actions (Clark & Semin Reference Clark and Semin2007).

In short, whether it is for computational purposes or for social interaction, language allows complex uses for otherwise simple elements and thoughts. Language not only allows new uses of people's outer worlds, but it also allows an “intellectual explosion” because of an exponential increase of the utility and potential of existing tools. Taken together, we think that the “discontinuity” between humans' and chimps' tool use may be misleading. Indeed, our suggestion seems to find support in work on conceptual knowledge; research shows that both for human and nonhuman animals, the presence of a specific object (e.g., a conspecific or food) activates knowledge distributed across modality-specific systems, rather than through modular and amodal systems (see Barsalou Reference Barsalou2005).

We have proposed that differences between humans and chimps in tool use are not due to a discontinuity between humans and chimps, but, instead, due to a vast discrepancy enabled by the language that provides immensely complex usages of otherwise relatively simple cognitive tools. Language thus complements otherwise basic biological abilities, thereby providing a key factor in the differentiation between humans and chimps.

For these reasons, language plays a fundamental role not only in the development of tool use, but also, and most importantly, in creating culture accumulation. Vaesen's discussion on cumulative culture surprisingly omits the important and, we argue, necessary role of language in building complex systems and in the development of human technology.