We find problems with Vaesen's treatment of the primatological research, in particular his analysis of foresight, function representation, and social intelligence. We argue that his criticism of research on foresight in great apes is misguided. His claim that primates do not attach functions to particular objects is also problematic. Finally, his analysis of theory of mind neglects many distinctions.

Contrary to Vaesen's argument that humans are unique with respect to nine cognitive capacities essential for tool use, we suggest that although such cognitive processes contribute to variation in tool use, it does not follow that these capacities are necessary for tool use, nor that tool use shaped cognition per se, given the available data in cognitive neuroscience and behavioral biology.

We are in vehement agreement with most of Vaesen's key claims. But Vaesen fails to consider or rebut the possibility that there are deep causal dependencies among the various cognitive traits he identifies as uniquely human. We argue that “higher-order relational reasoning” is one such linchpin trait in the evolution of human tool use, social intelligence, language, and culture.

Vaesen infers unique properties of mind from the appearance of specific cultural innovation – a correlation without causal direction. Shifts in habitat, population density, and group dynamics are the only independently verifiable incentives for changes in cultural practices. The transition from Acheulean to Late Stone Age technologies requires that we consider how population and social dynamics affect cultural innovation and mental function.

Evolutionary questions require specialized approaches, part of which are comparisons between close relatives. However, to understand the origins of human tool behavior, comparisons with solely chimpanzees are insufficient, lacking the power to identify derived traits. Moreover, tool use is unlikely a unitary phenomenon. Large-scale comparative analyses provide an alternative and suggest that tool use co-evolves with a suite of cognitive traits.

Vaesen argues that functional knowledge differentiates humans from non-human primates. However, the rationale he provides for this position is open to question – with respect to both the underlying theoretical assumptions and inferences drawn from certain empirical studies. Indeed, there is some recent empirical work that suggests that functional fixedness is not necessarily uniquely human. I also question the central role of stable function representations in Vaesen's account of tool production and use.

Comparing cognitive functions between humans and nonhuman primates is helpful for understanding human tool use. We comment on the latest insights from comparative research on executive control functions. Based on our own work, we discuss how even a mental function in which non-human primates outperform humans might have played a key role in the development of tool use.

We agree with Vaesen that there is evidence for cognitive differences between humans and other primates. However, it is too early to draw firm conclusions about the uniqueness of the cognitive mechanisms underlying human tool use. Tests of causal understanding are in their infancy, as is the study of animals more distantly related to humans.

Contrary to Vaesen, we argue that a small number of key traits are sufficient to explain modern human tool use. Here we outline and defend the cultural intelligence (CI) hypothesis. In doing so, we critically re-examine the role of social transmission in explaining human tool use.

Investigation of the cerebral organization of cognition in modern humans may serve as a tool for a better understanding of the evolutionary origins of our unique cognitive abilities. This commentary suggests three approaches that may serve this purpose: (1) cross-task neural overlap, referred to by Vaesen; but also (2) co-lateralization of asymmetric cognitive functions and (3) cross-functional (effective) connectivity.

Vaesen asks whether goal maintenance and planning ahead are critical for innovative tool use. We suggest that these aptitudes may have an evolutionary foundation in motor planning abilities that span all primate species. Anticipatory effects evidenced in the reaching behaviors of lemurs, tamarins, and rhesus monkeys similarly bear on the evolutionary origins of foresight as it pertains to tool use.

In my response to the commentaries from a collection of esteemed researchers, I reassess and eventually find largely intact my claim that human tool use evidences higher social and non-social cognitive ability. Nonetheless, I concede that my examination of individual-level cognitive traits does not offer a full explanation of cumulative culture yet. For that, one needs to incorporate them into population-dynamic models of cultural evolution. I briefly describe my current and future work on this.