In his target article, Vaesen attempts to find a set of intrinsic cognitive traits, often described in terms of neurological structures, that help explain the divergent paths with respect to tool use taken by humans and non-human primates. The emphasis here seems to be skewed in the direction of intrinsic traits at the expense of ecological contexts. Yet, as Rosen (Reference Rosen2000) pointed out succinctly, a function of an organism can never be understood in terms of its internal structure, because “a function requires an external context; a structure does not” (p. 25). I do agree with Vaesen that “no individual cognitive trait can be singled out as the key trait differentiating humans from other animals” (sect. 1). However, it is not that multiple cognitive traits differentiate humans from nonhuman primates, but that species are never adequately differentiated by means of such essentialistic criteria (Ghiselin Reference Ghiselin1974; Reed Reference Reed1996).
The examples that illustrate the inadequacy of the assumption of simple mapping between intrinsic traits and functional behavior range from the convergence of nut-cracking behavior in extant primate species, where both 45-kg chimpanzees (Pan troglodytes) and 3-kg capuchin monkeys (Cebus libidinosus) use stone hammers around 1 kg in mass (Haslam et al. Reference Haslam, Hernandez-Aguilar, Ling, Carvalho, de la Torre, DeStefano, Du, Hardy, Harris, Marchant, Matsuzawa, McGrew, Mercader, Mora, Petraglia, Roche, Visalberghi and Warren2009), to upland geese with webbed feet that never go near the water. The latter were observed by Darwin (Reference Darwin1859), who remarked, “habits have changed without a corresponding change of structure” (p. 186).
In human evolution, the time gap between the start of stone flaking and the earliest Homo fossils suggests that earlier hominin taxa (i.e., Australopithecus) could be the makers of the earliest stone tools (McPherron et al. Reference McPherron, Alemseged, Marean, Wynn, Reed, Geraads, Bobe and Béarat2010; Plummer Reference Plummer2004), whose relative brain sizes appear to be roughly equivalent to those of the extant great apes (Asfaw et al. Reference Asfaw, White, Lovejoy, Latemer, Simpson and Suwa1999; Kappelman Reference Kappelman1996). Recent discovery of 1.76-million-year-old early Acheulean tools, which pre-date the oldest known out-of-Africa hominin sites with no such artifacts, provides evidence that at least two contemporaneous hominin groups coexisted in Africa at that time: one with early Acheulean technology who remained in Africa and the other without such technology who developed strategies for dispersion into Eurasia (Lepre et al. Reference Lepre, Roche, Kent, Harmand, Quinn, Brugal, Texier, Lenoble and Feibel2011). Whether this indicates the cultural disparity within species or the existence of separate species is unknown, but I seriously doubt that such division can be caused by the preceding changes in their “cognitive” capacities alone.
Today, there is increasing evidence to suggest that changes in behavior that establish a new environmental relationship often antedate genetic, physiological, or morphological changes; and behavior is viewed as one of the leading edges of evolution, rather than simply the end product of it (Gottlieb Reference Gottlieb2002; Plotkin Reference Plotkin1988). The recurrence of new environmental relationships may influence the selection pressures on species, favoring individuals with phenotypes that match the usage of novel behavioral resources of the environment (Lewontin Reference Lewontin, Oyama, Griffiths and Gray2001; Odling-Smee et al. Reference Odling-Smee, Laland and Feldman2003). A consensus among researchers holds that novel behavioral shifts associated with the discovery of conchoïdal fracture, which allowed for meat and marrow procurement by means of sharp-edged tools, played instrumental selective roles during human evolution (Asfaw et al. Reference Asfaw, White, Lovejoy, Latemer, Simpson and Suwa1999; Bril et al. Reference Bril, Rein, Nonaka, Wenban-Smith and Dietrich2010; Isaac Reference Isaac, Coppens, Howell, Isaac and Leakey1976; McPherron et al. Reference McPherron, Alemseged, Marean, Wynn, Reed, Geraads, Bobe and Béarat2010; Roche Reference Roche, Roux and Bril2005; Semaw et al. Reference Semaw, Renne, Harris, Feibel, Bernor, Fesseha and Mowbray1997; Stout et al. Reference Stout, Semaw, Rogers and Cauche2010).
Our own experimental study on this particular way of exploiting behavioral resources in the environment – the control of conchoïdal fracture in flaking through direct hard-hammer percussion – revealed the necessity of considerable amount of experience in predicting and controlling the consequence of a strike given to a core (Nonaka et al. Reference Nonaka, Bril and Rein2010). This requires seeking out the relevant features in the surface structure of the core that reflect the constraints of conchoïdal fracture. Specifically, modern experienced stone knappers have discovered a regularity that exists in the relationship between the observable layout of surfaces of the core, size of a detachable flake, and threshold of kinetic energy required to initiate the fracture, which was demonstrated by the selection of striking location and the control of movement. Essential to the acquisition of this kind of skill is the firsthand experience to explore the properties of a core and a hammer stone. We suggested that the evidence of precise control of conchoïdal fracture in the Early Stone Age records (e.g., Delanges & Roche Reference Delanges and Roche2005) may be indicative of the recurrence of a situation in which juveniles are provided with the experience of rediscovering important affordances of the environment directly, by looking at the surface of the core and wielding the hammer stone.
Vaesen does rightly emphasize the role of social learning in human technological accumulation. However, what exists in the environment (outside of the head) that “motivates” the accumulation of knowledge across generations is largely left out of his account. Among the nut-cracking populations of wild chimpanzees, for example, the same stone tools have been re-used over successive generations (S. Hirata and S. Carvalho personal communication). Capuchins are known to accumulate stones that are appropriate for the nut-cracking task at sites with appropriate anvils, the remains of which may last for millennia (Visalberghi et al. Reference Visalberghi, Fragaszy, Ottoni, Izar, de Oliveira and Andrade2007). In such cases, not only the ecological “givens” but also the ecological “takings” and “makings” make up the facts of the physical world that surrounds evolving populations of animals (Reed Reference Reed1996). These facts of the environment are no less biological and no more cultural than neurological structures and genes are, which are equally incorporated into, and thereby contribute to, the furtherance of various biological processes of animals.
What makes a particular behavior such as tool use occur as it does is a result of how that behavior has evolved in the environment, selected and modified by a unique population (Gibson Reference Gibson1986; Reed Reference Reed, Johnston and Pietrewicz1985). Given the primacy of the environment into which animals are born toward the use of which behavior evolves, I would welcome Vaesen's making a connection between his ideas and the following question: What exists in the environment that motivates the emergence, transmission, and sophistication of tool use?
In his target article, Vaesen attempts to find a set of intrinsic cognitive traits, often described in terms of neurological structures, that help explain the divergent paths with respect to tool use taken by humans and non-human primates. The emphasis here seems to be skewed in the direction of intrinsic traits at the expense of ecological contexts. Yet, as Rosen (Reference Rosen2000) pointed out succinctly, a function of an organism can never be understood in terms of its internal structure, because “a function requires an external context; a structure does not” (p. 25). I do agree with Vaesen that “no individual cognitive trait can be singled out as the key trait differentiating humans from other animals” (sect. 1). However, it is not that multiple cognitive traits differentiate humans from nonhuman primates, but that species are never adequately differentiated by means of such essentialistic criteria (Ghiselin Reference Ghiselin1974; Reed Reference Reed1996).
The examples that illustrate the inadequacy of the assumption of simple mapping between intrinsic traits and functional behavior range from the convergence of nut-cracking behavior in extant primate species, where both 45-kg chimpanzees (Pan troglodytes) and 3-kg capuchin monkeys (Cebus libidinosus) use stone hammers around 1 kg in mass (Haslam et al. Reference Haslam, Hernandez-Aguilar, Ling, Carvalho, de la Torre, DeStefano, Du, Hardy, Harris, Marchant, Matsuzawa, McGrew, Mercader, Mora, Petraglia, Roche, Visalberghi and Warren2009), to upland geese with webbed feet that never go near the water. The latter were observed by Darwin (Reference Darwin1859), who remarked, “habits have changed without a corresponding change of structure” (p. 186).
In human evolution, the time gap between the start of stone flaking and the earliest Homo fossils suggests that earlier hominin taxa (i.e., Australopithecus) could be the makers of the earliest stone tools (McPherron et al. Reference McPherron, Alemseged, Marean, Wynn, Reed, Geraads, Bobe and Béarat2010; Plummer Reference Plummer2004), whose relative brain sizes appear to be roughly equivalent to those of the extant great apes (Asfaw et al. Reference Asfaw, White, Lovejoy, Latemer, Simpson and Suwa1999; Kappelman Reference Kappelman1996). Recent discovery of 1.76-million-year-old early Acheulean tools, which pre-date the oldest known out-of-Africa hominin sites with no such artifacts, provides evidence that at least two contemporaneous hominin groups coexisted in Africa at that time: one with early Acheulean technology who remained in Africa and the other without such technology who developed strategies for dispersion into Eurasia (Lepre et al. Reference Lepre, Roche, Kent, Harmand, Quinn, Brugal, Texier, Lenoble and Feibel2011). Whether this indicates the cultural disparity within species or the existence of separate species is unknown, but I seriously doubt that such division can be caused by the preceding changes in their “cognitive” capacities alone.
Today, there is increasing evidence to suggest that changes in behavior that establish a new environmental relationship often antedate genetic, physiological, or morphological changes; and behavior is viewed as one of the leading edges of evolution, rather than simply the end product of it (Gottlieb Reference Gottlieb2002; Plotkin Reference Plotkin1988). The recurrence of new environmental relationships may influence the selection pressures on species, favoring individuals with phenotypes that match the usage of novel behavioral resources of the environment (Lewontin Reference Lewontin, Oyama, Griffiths and Gray2001; Odling-Smee et al. Reference Odling-Smee, Laland and Feldman2003). A consensus among researchers holds that novel behavioral shifts associated with the discovery of conchoïdal fracture, which allowed for meat and marrow procurement by means of sharp-edged tools, played instrumental selective roles during human evolution (Asfaw et al. Reference Asfaw, White, Lovejoy, Latemer, Simpson and Suwa1999; Bril et al. Reference Bril, Rein, Nonaka, Wenban-Smith and Dietrich2010; Isaac Reference Isaac, Coppens, Howell, Isaac and Leakey1976; McPherron et al. Reference McPherron, Alemseged, Marean, Wynn, Reed, Geraads, Bobe and Béarat2010; Roche Reference Roche, Roux and Bril2005; Semaw et al. Reference Semaw, Renne, Harris, Feibel, Bernor, Fesseha and Mowbray1997; Stout et al. Reference Stout, Semaw, Rogers and Cauche2010).
Our own experimental study on this particular way of exploiting behavioral resources in the environment – the control of conchoïdal fracture in flaking through direct hard-hammer percussion – revealed the necessity of considerable amount of experience in predicting and controlling the consequence of a strike given to a core (Nonaka et al. Reference Nonaka, Bril and Rein2010). This requires seeking out the relevant features in the surface structure of the core that reflect the constraints of conchoïdal fracture. Specifically, modern experienced stone knappers have discovered a regularity that exists in the relationship between the observable layout of surfaces of the core, size of a detachable flake, and threshold of kinetic energy required to initiate the fracture, which was demonstrated by the selection of striking location and the control of movement. Essential to the acquisition of this kind of skill is the firsthand experience to explore the properties of a core and a hammer stone. We suggested that the evidence of precise control of conchoïdal fracture in the Early Stone Age records (e.g., Delanges & Roche Reference Delanges and Roche2005) may be indicative of the recurrence of a situation in which juveniles are provided with the experience of rediscovering important affordances of the environment directly, by looking at the surface of the core and wielding the hammer stone.
Vaesen does rightly emphasize the role of social learning in human technological accumulation. However, what exists in the environment (outside of the head) that “motivates” the accumulation of knowledge across generations is largely left out of his account. Among the nut-cracking populations of wild chimpanzees, for example, the same stone tools have been re-used over successive generations (S. Hirata and S. Carvalho personal communication). Capuchins are known to accumulate stones that are appropriate for the nut-cracking task at sites with appropriate anvils, the remains of which may last for millennia (Visalberghi et al. Reference Visalberghi, Fragaszy, Ottoni, Izar, de Oliveira and Andrade2007). In such cases, not only the ecological “givens” but also the ecological “takings” and “makings” make up the facts of the physical world that surrounds evolving populations of animals (Reed Reference Reed1996). These facts of the environment are no less biological and no more cultural than neurological structures and genes are, which are equally incorporated into, and thereby contribute to, the furtherance of various biological processes of animals.
What makes a particular behavior such as tool use occur as it does is a result of how that behavior has evolved in the environment, selected and modified by a unique population (Gibson Reference Gibson1986; Reed Reference Reed, Johnston and Pietrewicz1985). Given the primacy of the environment into which animals are born toward the use of which behavior evolves, I would welcome Vaesen's making a connection between his ideas and the following question: What exists in the environment that motivates the emergence, transmission, and sophistication of tool use?