The Gestural Origins of Language
Human language may have evolved from manual gestures, which survive today as a "behavioral fossil" coupled to speech
From Hand to Mouth
If language originated in manual gestures, why do modern-day human beings speak? Although the early hominids would have been much better preadapted to manual communication, and silent signs may have been preferred on the savanna, there were surely eventual advantages to switching to vocalization. For one thing, speech can be carried on in the dark, or when obstacles prevent communicating parties from viewing one another, or over relatively long distances. Goldin-Meadow and her colleagues have made the further point that if hands and voice are to share the burden of communication, it is more efficient for syntax to carry the grammatical component, leaving the iconic component to the hands, than to have the hands carry syntax as well as meaning. More importantly, perhaps, speech would have freed the hands yet again, allowing our ancestors to verbally instruct others in manual arts, such as the use and manufacture of tools, while at the same time demonstrating them.
It is unlikely that the switch from gestural to spoken language was sudden. Vocalized grunts and squeals would surely have punctuated early gestural language, just as gestures embellish modern vocal language—especially, one is tempted to observe, among the Italians. But vocal communication would have required extensive alterations to the vocal tract, as well as a shift from predominantly subcortical to cortical control over vocalization. As Philip Lieberman has argued, these alterations were probably not complete until relatively late in hominid evolution, perhaps only with the emergence of H. sapiens some 100,000 to 150,000 years ago. Moreover, spoken language requires more precise programming of motor sequences, since the message depends exclusively on temporal sequencing. In sign language, by contrast, grammatical information is often conveyed in parallel with other aspects of the message. For example, a sentence may be converted from a statement to a question by raising the eyebrows while the sentence is signed or into a negative by shaking the head. The pressure for accurate timing in the speech signal may well have sharpened selection for unilateral control, since any relaying of neural information between the two sides of the brain would result in some loss of temporal precision.
According to this scenario it was not language that uniquely characterized H. sapiens, but rather the shift to a form of expression in which vocalization could carry the primary communicative burden, including the all-important grammatical component. It may indeed have been "Eve" who spoke, but her predecessors probably communicated effectively with a combination of gestures and vocalizations.
Language may well have begun to evolve as a generative, grammatical system from the emergence of the genus Homo over 2 million years ago. In early Homo we see the first clear signs of an increase in brain size and the first evidence for manufactured stone tools. But although stone tools became somewhat more sophisticated in succeeding species of Homo, technology appears to have been remarkably static for almost two million years—held back, perhaps, by the involvement of the hands in communication. By the reckoning of some, it was not until the Aurignacian period in Europe, beginning some 40,000 years ago, that tools began to display a greater variety and sophistication. However, the emergence of sophisticated technology in Europe appears to have coincided with the arrival in Europe of H. sapiens, which eventually replaced the incumbent Neanderthals. Recent discoveries, including 90,000-year-old artifacts made of bone in Zaire, suggest that the technological revolution began much earlier and may have been initiated by H. sapiens in Africa.
It is now considered likely that H. sapiens emerged in Africa and radiated from there sometime between 60,000 and 100,000 years ago, replacing other hominid species who had migrated earlier, including the Neanderthals in Europe and Homo erectus, who may have persisted in Java until as recently as 27,000 years ago. What was it that enabled our species to prevail over these other large-brained hominids, whose forebears had migrated much earlier? Perhaps the most plausible answer is that they prevailed because of superior technology. But that technology might have resulted, not from an increase in brain size or intelligence, but from a switch from manual to vocal language that allowed them to use their hands for the manufacture of tools and weapons and their voices for instruction.
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