Although once considered a prime hallmark of humanity, tool making has, in recent decades, often been relegated to the ranks of unintelligent behaviors well within the capacity of other animals. Instead, some now postulate that the distinguishing feature of humanity is another specific cognitive capacity, such as theory of mind, cooperation, or syntactical language. Vaesen provides an important service to evolutionary scholars by emphasizing two points. (1) Human technological accomplishments far exceed those of chimpanzees. (2) Human excellence reflects a host of advanced, interacting cognitive and motor skills, as opposed to the possession of a single unique cognitive, motor, or social capacity.
Whether human versus ape technological and associated capacities should be labeled “discontinuities” will, however, remain a matter of debate. Behavioral continuities and discontinuities, like beauty, reside in the minds of beholders. Many investigators, for example, routinely interpret animal behaviors within the context of Morgan's Canon. This essentially assures that most animal behaviors will be interpreted as unintelligent – hence, discontinuous with those of humans. Other investigators begin with assumptions that all human cognitive skills derive from animal precursors – and hence, are continuous. Differences also derive from the nature of the observed data. Investigators who primarily study cage-reared animals seem to routinely judge chimpanzees and other apes to be less capable of human-like behaviors than do investigators who study human-reared or wild animals. Similarly, those who study the cognitive and linguistic skills of human infants often seem more open to continuity views than are those who focus on the competencies only of adults or older children. Investigators' views on brain function, however, may be of paramount importance. Assumptions that most unique human behaviors reflect genetically determined, behaviorally specific neural modules predispose to interpretations of discontinuities. In contrast, a focus on developmental neural plasticity and probable brain size–related influences on behavioral functions may predispose to continuity perspectives.
I have previously postulated behavioral continuities between great apes and humans based on three primary considerations (Gibson Reference Gibson1991; Reference Gibson, Gibson and Ingold1993; Reference Gibson, Lock and Peters1996; Reference Gibson2002; Gibson & Jessee Reference Gibson, Jessee and King1999): (1) Most traits postulated as uniquely human are eventually found to occur in more rudimentary forms in other animals including great apes: for example, tool making, symbolism, theory of mind, deception, cooperation, culture. In most instances, ape/human differences appear to relate primarily to differences in the amount of information that can be brought to bear on each task and then hierarchically synthesized into new cognitive constructions. (2) Neo-Piagetian perspectives, such as those of the late Robbie Case (Reference Case1985), postulate quite similar developmental changes across a variety of behavioral domains in maturing human infants and children. Case interpreted these cognitive changes as reflections of developmental increases in information-processing capacities. (3) Irrespective of whatever reorganizational changes may have occurred in the human brain, the most obvious ape/human neuroanatomical differences relate to the overall size of the brain and of many of its component parts (Gibson Reference Gibson, Parker and Gibson1990; Reference Gibson2002; Gibson & Jessee Reference Gibson, Jessee and King1999; Gibson et al. Reference Gibson, Rumbaugh, Beran, Falk and Gibson2001) and hence, to probable increases in information-processing capacities throughout much of the brain. The archaeological and paleontological records indicate gradual increases in both brain size and hierarchical capacities, and hence, a probable continuing process of increased information-processing capacities resulting in increasingly advanced cognitive and motor skills. Nonetheless, I view the differences between ape and human behaviors as quite large, much as Vaesen does. Therefore, investigators can have similar views about the distinctions between ape and human capacities, and nonetheless draw different conclusions about continuity or lack thereof. Perhaps, then, they should simply focus on clearly articulating observed animal/human differences and the cognitive and neurological mechanisms perceived to underlie them, rather than on potentially fruitless continuity arguments.
Even if one adopts the information-processing and hierarchical constructional approach, other issues remain. Did hierarchical information-processing capacities evolve first in the tool-using domain and then transfer to other domains (a view Vaesen erroneously attributes to me); did advanced information-processing capacities evolve separately in each behavioral domain; or is hierarchical construction a domain-general process that increased simultaneously in all behavioral domains? Current behavioral and neurological evidence is insufficient to provide a definitive answer to such questions. As Vaesen points out, given that it is the interaction of many advanced human behavioral capacities that distinguishes humans, and in all probability, later fossil hominins from apes, it seems to me most likely that information-processing capacity increased synchronously in many domains.
Vaesen also questions evolutionary relationships between gesture and tool use. Again, he erroneously attributes a hypothesis to me – that manual dexterity first evolved for tool use and then was transferred to the gestural domain. Current evidence seems, if anything, more compatible with the opposite view. In apes, laterality (one component of manual dexterity) is more pronounced in the gestural than in the tool-using domain (Hopkins & Vauclair Reference Hopkins, Vauclair, Tallerman and Gibson2011). At one time, I did adhere to Gordon Hewes's hypothesis that hominin-like gestural communication systems evolved earlier than did hominin-like vocal communication systems (Hewes Reference Hewes1973; Parker& Gibson Reference Parker and Gibson1979). This hypothesis, which was based on earlier views that ape gestural capacities exceed their vocal capacities, no longer seems necessary. Recent research indicates that great ape vocal learning capacities are much greater than were previously believed (Slocombe Reference Slocombe, Tallerman and Gibson2011). Moreover, gestural and vocal communications are inextricably linked in modern humans (Goldin-Meadow Reference Goldin-Meadow, Tallerman and Gibson2011) and probably were similarly linked throughout human evolution. To the extent that human tool making, communicative, and advanced social behaviors involve similar hierarchical mental constructional capacities and may all have evolved in relationship to the invasion of new foraging niches such as omnivorous extractive foraging (Parker & Gibson Reference Parker and Gibson1979), hunting (Vaesen), and/or scavenging (Bickerton Reference Bickerton2009), it seems most likely that advanced communicative (gestural and vocal), social, and tool-making capacities evolved together as one complex whole.
Although once considered a prime hallmark of humanity, tool making has, in recent decades, often been relegated to the ranks of unintelligent behaviors well within the capacity of other animals. Instead, some now postulate that the distinguishing feature of humanity is another specific cognitive capacity, such as theory of mind, cooperation, or syntactical language. Vaesen provides an important service to evolutionary scholars by emphasizing two points. (1) Human technological accomplishments far exceed those of chimpanzees. (2) Human excellence reflects a host of advanced, interacting cognitive and motor skills, as opposed to the possession of a single unique cognitive, motor, or social capacity.
Whether human versus ape technological and associated capacities should be labeled “discontinuities” will, however, remain a matter of debate. Behavioral continuities and discontinuities, like beauty, reside in the minds of beholders. Many investigators, for example, routinely interpret animal behaviors within the context of Morgan's Canon. This essentially assures that most animal behaviors will be interpreted as unintelligent – hence, discontinuous with those of humans. Other investigators begin with assumptions that all human cognitive skills derive from animal precursors – and hence, are continuous. Differences also derive from the nature of the observed data. Investigators who primarily study cage-reared animals seem to routinely judge chimpanzees and other apes to be less capable of human-like behaviors than do investigators who study human-reared or wild animals. Similarly, those who study the cognitive and linguistic skills of human infants often seem more open to continuity views than are those who focus on the competencies only of adults or older children. Investigators' views on brain function, however, may be of paramount importance. Assumptions that most unique human behaviors reflect genetically determined, behaviorally specific neural modules predispose to interpretations of discontinuities. In contrast, a focus on developmental neural plasticity and probable brain size–related influences on behavioral functions may predispose to continuity perspectives.
I have previously postulated behavioral continuities between great apes and humans based on three primary considerations (Gibson Reference Gibson1991; Reference Gibson, Gibson and Ingold1993; Reference Gibson, Lock and Peters1996; Reference Gibson2002; Gibson & Jessee Reference Gibson, Jessee and King1999): (1) Most traits postulated as uniquely human are eventually found to occur in more rudimentary forms in other animals including great apes: for example, tool making, symbolism, theory of mind, deception, cooperation, culture. In most instances, ape/human differences appear to relate primarily to differences in the amount of information that can be brought to bear on each task and then hierarchically synthesized into new cognitive constructions. (2) Neo-Piagetian perspectives, such as those of the late Robbie Case (Reference Case1985), postulate quite similar developmental changes across a variety of behavioral domains in maturing human infants and children. Case interpreted these cognitive changes as reflections of developmental increases in information-processing capacities. (3) Irrespective of whatever reorganizational changes may have occurred in the human brain, the most obvious ape/human neuroanatomical differences relate to the overall size of the brain and of many of its component parts (Gibson Reference Gibson, Parker and Gibson1990; Reference Gibson2002; Gibson & Jessee Reference Gibson, Jessee and King1999; Gibson et al. Reference Gibson, Rumbaugh, Beran, Falk and Gibson2001) and hence, to probable increases in information-processing capacities throughout much of the brain. The archaeological and paleontological records indicate gradual increases in both brain size and hierarchical capacities, and hence, a probable continuing process of increased information-processing capacities resulting in increasingly advanced cognitive and motor skills. Nonetheless, I view the differences between ape and human behaviors as quite large, much as Vaesen does. Therefore, investigators can have similar views about the distinctions between ape and human capacities, and nonetheless draw different conclusions about continuity or lack thereof. Perhaps, then, they should simply focus on clearly articulating observed animal/human differences and the cognitive and neurological mechanisms perceived to underlie them, rather than on potentially fruitless continuity arguments.
Even if one adopts the information-processing and hierarchical constructional approach, other issues remain. Did hierarchical information-processing capacities evolve first in the tool-using domain and then transfer to other domains (a view Vaesen erroneously attributes to me); did advanced information-processing capacities evolve separately in each behavioral domain; or is hierarchical construction a domain-general process that increased simultaneously in all behavioral domains? Current behavioral and neurological evidence is insufficient to provide a definitive answer to such questions. As Vaesen points out, given that it is the interaction of many advanced human behavioral capacities that distinguishes humans, and in all probability, later fossil hominins from apes, it seems to me most likely that information-processing capacity increased synchronously in many domains.
Vaesen also questions evolutionary relationships between gesture and tool use. Again, he erroneously attributes a hypothesis to me – that manual dexterity first evolved for tool use and then was transferred to the gestural domain. Current evidence seems, if anything, more compatible with the opposite view. In apes, laterality (one component of manual dexterity) is more pronounced in the gestural than in the tool-using domain (Hopkins & Vauclair Reference Hopkins, Vauclair, Tallerman and Gibson2011). At one time, I did adhere to Gordon Hewes's hypothesis that hominin-like gestural communication systems evolved earlier than did hominin-like vocal communication systems (Hewes Reference Hewes1973; Parker& Gibson Reference Parker and Gibson1979). This hypothesis, which was based on earlier views that ape gestural capacities exceed their vocal capacities, no longer seems necessary. Recent research indicates that great ape vocal learning capacities are much greater than were previously believed (Slocombe Reference Slocombe, Tallerman and Gibson2011). Moreover, gestural and vocal communications are inextricably linked in modern humans (Goldin-Meadow Reference Goldin-Meadow, Tallerman and Gibson2011) and probably were similarly linked throughout human evolution. To the extent that human tool making, communicative, and advanced social behaviors involve similar hierarchical mental constructional capacities and may all have evolved in relationship to the invasion of new foraging niches such as omnivorous extractive foraging (Parker & Gibson Reference Parker and Gibson1979), hunting (Vaesen), and/or scavenging (Bickerton Reference Bickerton2009), it seems most likely that advanced communicative (gestural and vocal), social, and tool-making capacities evolved together as one complex whole.