In an effort to understand the origins of human tool behavior, investigators have focused on tool behavior in primates, especially in chimpanzees. Nevertheless, tool behavior is widespread and complex in the animal world, as indicated by the survey of Shumaker et al. (Reference Shumaker, Walkup and Beck2011). This demonstrates that tool behavior evolves through convergent evolution, a point that is most cogently made by examining its presence in capuchin monkeys and birds (Emery & Clayton Reference Emery and Clayton2004; Fragaszy et al. Reference Fragaszy, Izar, Visalberghi, Ottoni, Gomes and Oliveira2004), as well as in the great apes. The intense focus on chimpanzees is driven by two factors. First, and most important, is the argument by ancestry: Chimpanzees are the closest living relatives of human beings. The second factor is comparatively trivial, but determines much research: If one studies chimpanzees – and they have received enormous attention for 50 years – any behavior that they demonstrate will be considered intrinsically important.

Vaesen does a remarkable job of assembling the array of evidence separating human tool behavior from the tool behavior of other animals. However, I believe that one line of evidence should have received more emphasis in the paper. In discussing causal reasoning, Vaesen briefly notes the experiments conducted by Povinelli et al. (Reference Povinelli, Reaux, Theall and Giambrone2000), and presents one example of these experiments (Fig. 1 of the target article). The total corpus of these experiments demonstrates a profound difference in cognition between humans and chimpanzees. The Povinelli monograph underscores the great gulf that exists between human causal reasoning and the reasoning abilities of chimpanzees. In fact, chimpanzees do not seem to have a “theory of how the world works.” If this is so, then it epitomizes the unique character of human tool behavior – that it is based on the unconscious, sophisticated knowledge of energy, movement, objects, and the interaction of objects that Povinelli et al. (Reference Povinelli, Reaux, Theall and Giambrone2000) label “folk physics.”

Vaesen elegantly dissects the factors underlying contingent reciprocity in Table 1 of the target article, and is right to point out potential problems with the existence of empathy in non-human primates. Sharing and exchange underlie the division of labor seen in humans, as well as human trade, which is seen indisputably in the archaeological record at about 40,000 years ago. The active teaching discussed by Vaesen is involved in human cultural transmission and the wide dispersal of human culture. Yet, active teaching certainly also underlies human cooperation, and one of the major differences between humans and other animals is that humans habitually cooperate in using and making tools.

In addition to the unique cognitive behaviors underlying human tool use that Vaesen notes, differences in behavior between humans and non-human primates can be documented with stone tools occurring at the earliest archaeological sites, dating to 2.6–2.5 mya. Studies of chimpanzee “archaeology” (e.g., Mercader et al. Reference Mercader, Panger and Boesch2002) only highlight the differences between humans and chimpanzees. Chimpanzees create microscopic stone shatter when they use hammer stones to pound open nuts, but they do not create stone artifacts. In spite of claims that chimpanzees create stone tools that are indistinguishable from the earliest tools in the archaeological record (McGrew Reference McGrew1992), chimpanzee “archaeology” emphatically demonstrates otherwise. Behaviors that frequently are typically associated with the origins of anatomically modern humans actually have a deep antiquity in the archaeological record, going back to at least 1.6–1.4 mya (Cachel Reference Cachel, Wilkins and Anderson2009). These include greater dispersal ability, spatial organization of behavior at archaeological sites, behavioral variability between sites, transport and curation of stone raw materials and animal carcasses, primary access to animal carcasses whether through hunting or confrontational scavenging, change in stone artifacts through time, and forethought or planning.