Bipedal Hominins

INTRODUCTION Although captive chimpanzees, bonobos and other great apes have acquired some of the features of There is fairly general agreement that language is a language, including the use of symbols to denote uniquely human accomplishment. Although other objects or actions, they have not displayed species communicate in diverse ways, human anything like recursive syntax, or indeed any language has properties that stand out as special. degree of generativity beyond the occasional 4 The most obvious of these is generativity -the ability combining of symbols in pairs. To quote Pinker, to construct a potentially infinite variety of they simply don’t “get it.” This suggests that the sentences, conveying an infinite variety of common ancestor of humans and chimpanzee was meanings. Animal communication is by contrast almost certainly bereft of anything we might stereotyped and restricted to particular situations, consider to be true language. Human language and typically conveys emotional rather than must therefore have evolved its distinctive propositional information. The generativity of characteristics over the past 6 million years. Some language was noted by Descartes as one of the have claimed that this occurred in a single step, characteristics separating humans from other and recently -perhaps as recently as 170,000 years species, and has also been emphasized more ago, coincident with the emergence of our own recently by Chomsky, as in the following often- species. This is sometimes referred to as the “big quoted passage: bang” theory of language evolution. For example, Bickerton5 asserted that “… true language, via the “The unboundedness of human speech, as an emergence of syntax, was a catastrophic event, expression of limitless thought, is an entirely occurring within the first few generations of Homo different matter (from animal communication), sapiens sapiens (p. 69).” Even more radically, 6 because of the freedom from stimulus control; and Crow has proposed that a genetic mutation gave the appropriateness to new situations… Modern rise to the speciation of Homo sapiens, along with studies of animal communication so far offer no such uniquely human attributes as language, counterevidence to the Cartesian assumption that cerebral asymmetry, theory of mind, and a human language is based on an entirely different vulnerability to psychosis. principle. Each known animal communication system either consists of a fixed number of signals, Against this is a more conventional Darwinian view each associated with a specific range of eliciting that language evolved in incremental fashion, systems or internal states, or a fixed number of through natural selection, as maintained by Pinker 7 8 ‘linguistic dimensions,’ each associated with a non- and Bloom and elaborated by Jackendoff. In this linguistic dimension.”1 article, I propose that there were three broad phases to the emergence of modern language, spanning More recently Chomsky, in a co-authored article, the past six million years. has acknowledged that some aspects of language may owe their origins to adaptations also present in Stage 1: Bipedal hominins other primates, but that the generative, recursive The journey toward articulate language began with nature of language is distinctively human.*2,3 the separation of the hominin line from that leading to modern chimpanzees and bonobos. The earliest Despite general agreement on this point, there is fossil skull tentatively identified as a bipedal hominin controversy over how and when language evolved. is Sahelanthropus tchadensis, discovered in Chad, * It has recently been claimed that starlings can parse recursive sequences, suggesting that phrase structure grammar may not be beyond the capacity of a nonhuman species. This claim is based on highly questionable evidence -see Corballis (in press). and dated between 6 and 7 million years ago.9 This triplets to make simple requests. Their vocabularies date is probably very close to the time of the may number in the hundreds, but this is of course chimpanzee-hominin split, estimated at between well short of the vocabulary attainable by humans, 6.3 and 7.7 million years ago by a DNA-DNA which numbers in the tens of thousands. Echoing hybridization technique.10 Another early fossil, Pinker, Bickerton5 wrote that “The chimps’ abilities at Orrorin tugenensis, is perhaps more securely anything one would want to call grammar were next identified as a hominin, and is dated from between to nil,” and has labeled this pre-grammatical level of 5.2 and 5.8 years ago.11 linguistic performance “protolanguage.” The feature that distinguished the hominins from Curiously, protolanguage has not been convincingly the great apes was bipedalism. The idea that demonstrated among great apes in the wild, bipedalism may have contributed to the evolution of although closer study of natural gestures may well language was well anticipated by the 19th century reveal greater sophistication than has hitherto been linguist Wilhelm von Humboldt: recorded. Nevertheless protolanguage may well form the platform from which true language “And suited, finally, to vocalization is the upright evolved, as proposed by Jackendoff.8 It is even posture of man, denied to animals; man is thereby possible that it was the discovery of protolanguage summoned, as it were, to his feet. For speech does not among the early hominins that drove bipedalism aim at hollow extensions in the ground, but demands itself, freeing up a manual system ready-made for to pour freely from the lips towards the person intentional action. addressed, to be accompanied by facial expression and demeanor and by gestures of the hand, and There are of course other possible explanations for thereby to surround itself at once with everything that the emergence of bipedalism, although none is proclaims man human - italics added.”12 completely satisfactory. One theory is that Although the upright stance might indeed have bipedalism evolved to allow more accurate throwing enhanced vocal communication, its more immediate and clubbing.16 Another controversial idea is that it and obvious effect would have been to free the was a product of an aquatic phase, in which the hands. Nonhuman primates, no doubt including our early hominins spent part of their existence wading immediate predecessors, also have a frontal stance, in water, perhaps foraging for food in rivers, lakes, but are quadrupedal rather than bipedal. Our nearest or the ocean side.17-19 The idea that bipedalism might primate relative, the chimpanzee, makes fairly have been driven by selection for more effective extensive use of manual gestures, and these are communication is also controversial, especially since arguably under more voluntary control than it implies that language itself evolved from manual vocalizations, which in nonhuman primates serve as gestures, rather than from vocal calls. emotional signals rather than propositional utterances. Attempts to teach chimpanzees and The gestural theory of language evolution 13 other great apes to talk have proved fruitless, but The idea that language may have evolved from some progress toward human-like language has manual gestures is nevertheless old, dating back at been accomplished using gestures, loosely based on least to Condillac,20 and was revived in a landmark 14 American Sign Language, or by having the animal article by Hewes.21 It has been increasingly 15 point to symbols on a keyboard. As noted above, advocated over the past decade.22-29 It is based on a the animals still don’t “get” the concept of grammar, number of considerations, and not merely on the but appear able to use abstract symbols to denote manual communicative capacities of great apes. objects and actions, and to combine them in pairs or The late William C. Stokoe based his argument for the gestural theory primarily on the now well- vocalization in nonhuman primates, suggesting that established fact that the signed languages of the the incorporation of vocalization into the system deaf have all the generativity and syntactic may have occurred late in hominin evolution -this is sophistication of spoken languages.30,31 Four discussed further below. The vocalizations of additional “facts,” he claimed, show further that nonhuman primates are probably largely automatic visible language must have preceded speech: and emotional, controlled by the limbic system rather than the cortex.34 Nevertheless there are cells 1. Sign languages still exist. in area F5 of the monkey that respond to the sounds 2. Spoken utterances often require visible signs in of certain actions, such as the tearing of paper or order to be fully understandable. the cracking of nuts.35 That is, the mirror system may 3. Only visible signs have natural links to concepts have been pre-adapted for the analysis of sound in and syntactic structures. terms of the actions that produced those sounds, 4. All human infants use gesture to communicate but not for vocalization itself. before they master the language of their caretakers, whether that is a spoken language or Stage 2: Large-brained Homo a signed language.29 The early bipedal hominins may well have communicated more effectively than their primate The theory has also received support from primate forebears, with the freeing of the hands and arms neurophysiology. Area F5 of the ventral premotor providing for a more extensive signaling capacity. cortex of the monkey is the homologue of Broca’s There is little reason to suppose, however, that they area, which in humans is involved in the production had evolved a form of communication beyond of vocal speech. In primates, however, area F5 has protolanguage. to do with manual action, not vocalization. Cells in F5 respond when the animal makes grasping The emergence of a more grammatical, generative movements with the hand or mouth, and a subset form of communication may have begun only with of those cells, dubbed “mirror neurons,” also fire the emergence of the genus Homo, from around 2 when the animal observes another individual million years ago.

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