Enhanced hand-eye coordination, social learning, teaching, language, and social intelligence undoubtedly contribute to the accumulation of advanced, human-like technologies, but are they required for tool use? For example, given the strong selection pressure for successful foraging, fine motor control over one's feeding apparatus, be it beak, trunk, or claw, may promote tool use (e.g., Kenward et al. Reference Kenward, Rutz, Weir and Kacelnik2006). Primates use their hands extensively while foraging, but many species lack hands (or analogs) yet regularly use tools. In fact, primate tool use accounts for only about 10% of documented cases of animal tool use (Bentley-Condit & Smith Reference Bentley-Condit and Smith2009). Furthermore, most tool-using animals do not, as far as we know, socially learn the behavior or possess other components of social intelligence deemed essential by Vaesen (e.g., Brockmann Reference Brockmann1985).

Although Vaesen's nine capacities provide mechanisms for tool use transmission, maintenance, and improvement, thereby advancing technology, they are not preconditions for tool use as such. Therefore, although human technological achievements are unique, Vaesen's capacities and tool use itself may not be.

Studies of behavioral trait evolution demand an appropriate comparison group (i.e., all hominoidea, all anthropoidea, or all primates), but surveying analogous behaviors in distant taxa can elucidate the ecological and evolutionary contexts of these traits. Vaesen focuses on great ape studies that support his claims and ignores conflicting data. He extensively refers to the (phylogenetically distant) monkey literature that suits his argument (e.g., Cummins-Sebree & Fragaszy Reference Cummins-Sebree and Fragaszy2005; Hauser Reference Hauser1997) and ignores relevant monkey and even ape studies that do not (e.g., Hauser et al. Reference Hauser, Pearson and Seelig2002; Santos et al. Reference Santos, Miller and Hauser2003; Whiten et al. Reference Whiten, Horner and de Waal2005; although Whiten et al. Reference Whiten, Horner and de Waal2005 is mentioned later in a different context). In fact, Whiten et al.'s (2005) study and a new study (Hanus et al. Reference Hanus, Mendes, Tennie and Call2011) may very well indicate functional fixedness in chimpanzees. The ape studies Vaesen does mention here are placed in Note 14, and one (Carvalho et al. Reference Carvalho, Biro, McGrew and Matsuzawa2009) provides a strong case of tool reuse.

Among more distant taxa, bottlenose dolphins in Shark Bay, Australia, reuse basket sponge tools for a little more than an hour, as presumably during that period the tool remains functional; but much beyond that, functionality is lost and the tool is discarded (Patterson & Mann Reference Patterson and Mann2011). Furthermore, functional fixedness is not necessarily a valuable cognitive trait and may even be inhibitory (e.g., Hanus et al. Reference Hanus, Mendes, Tennie and Call2011). Flexibility, on the other hand, is a cognitive bonus, as with little to no modification a single tool becomes many (e.g., chimpanzees use sticks to fish for termites, honey [Fay & Carroll Reference Fay and Carroll1994], and ants [McGrew Reference McGrew1974] and even as hunting spears [Pruetz & Bertolani Reference Pruetz and Bertolani2007]). When discussing executive control and forethought, Vaesen focuses on ape studies by Osvath and Osvath (Reference Osvath and Osvath2008) but fails to mention other ape research (e.g., Biro & Matsuzawa Reference Biro and Matsuzawa1999; Boesch Reference Boesch1994; Boesch & Boesch Reference Boesch and Boesch1989; Dufour & Sterck Reference Dufour and Sterck2008; Noser & Byrne Reference Noser and Byrne2010; Osvath Reference Osvath2008). Vaesen does mention two additional studies, but again they are buried, in Note 20 rather than in the main body of his text. In fact, conflicting literature is repeatedly placed in notes (e.g., hand-eye coordination [5], functional representation [14], executive control and forethought [20], heuristics for selecting models for social learning [29], and food sharing [31]).

While not implicitly stating it, Vaesen strongly implies that human tool use and his nine capacities coevolved. If so, then Vaesen must address whether the phenotype was selected for and whether its current utility is the same as its historic use (Gould & Lewontin Reference Gould and Lewontin1979). Human technology is obviously indicative of higher cognitive ability, but may be a product of our cognition rather than the selective force behind it. Two other well-established brain evolution theories deserve consideration: the social brain hypothesis (Byrne & Whiten Reference Byrne and Whiten1988; Dunbar Reference Dunbar1998) and the ecological complexity hypothesis (Reader & Laland Reference Reader and Laland2002). Although tool use likely played a role in our cognitive evolution, either as a product or as a driving factor, it demands a systematic and comprehensive approach.

Finally, most of Vaesen's arguments rely on a lack of evidence, rather than evidence of absence (de Waal & Ferrari Reference de Waal and Ferrari2010). This amounts to trying to prove the null hypothesis, a nearly futile task when comparing across taxa because of (1) a lack of data for some species, (2) low ecological validity, (3) poor internal validity due to poorly designed tasks, (4) biases in research effort, and (5) the sheer difficulty of researching cognition in animals. Vaesen even admits, but is not deterred by the fact, that for 8 of the 16 traits he claims are decidedly more pronounced in humans than in chimpanzees, few data are available (Table 2).

Tool use should be studied with a comparative approach, including the examination of other taxa and analogous behaviors, and by maintaining an appreciation for the ecological and social contexts in which tool use arises (de Waal & Ferrari Reference de Waal and Ferrari2010). For example, Povinelli's studies on captive chimpanzees using human behavioral models fail to show causal reasoning (but see Call Reference Call, Lonsdorf, Ross, Matsuzawa and Goodall2010), whereas Cheney and Seyfarth's (Reference Cheney and Seyfarth1995) study with wild baboons, which uses more relevant tests, seems to demonstrate causal reasoning in natural social contexts. With more appropriate tests, apes may very well excel (albeit, not to the level of humans) in all of the nine capacities. Non-primates, such as rats, crows, and likely elephants, show causal reasoning (Blaisdell et al. Reference Blaisdell, Sawa, Leising and Waldmann2006; Plotnik et al. Reference Plotnik, Lair, Suphachoksahakun and de Waal2011; Taylor et al. Reference Taylor, Hunt, Medina and Gray2009a).

Other areas that could benefit from this comparative approach include, but are not limited too, imitation (e.g., dolphins; Herman Reference Herman, Dautenhahn and Nehaniv2002), social learning (e.g., woodpecker finches; Tebbich et al. Reference Tebbich, Taborsky, Fessl and Blomqvist2001), social intelligence (e.g., dolphins; Connor Reference Connor2007), insight learning (e.g., crows; Taylor et al. Reference Taylor, Elliffe, Hunt and Gray2010), forethought (e.g., dolphins; McCowan et al. Reference McCowan, Marino, Vance, Walke and Reiss2000), teaching (e.g., meerkats; Thornton & McAuliffe Reference Thornton and McAuliffe2006), inhibition (e.g., rodents, birds, and marine invertebrates; Dally et al. Reference Dally, Emery and Clayton2010; Kim Reference Kim2010; Vander Wall et al. Reference Vander Wall, Enders and Waitman2009), food sharing (e.g., killer whales; Ford & Ellis Reference Ford and Ellis2006), and theory of mind (e.g., dolphins and elephants; Douglas-Hamilton et al. Reference Douglas-Hamilton, Bhalla, Wittemyer and Vollrath2006; Plotnik et al. Reference Plotnik, de Waal, Moore and Reiss2010; Xitco et al. Reference Xitco, Gory and Kuczaj2004).

Surely those without hands deserve another look.