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Feature

From Hand to Mouth

A gesture speaks a thousand words

Michael Corballis

Our capacity to speak coherently and to understand the speech of others is an extraordinary accomplishment, well beyond even the most powerful of today's computers. It is also unique to human beings.

So far as we know, no other species has the ability to generate entirely novel sentences that are easily understood by listeners who have never heard them before. Indeed, I suspect that the reader is encountering this very sentence for the first time, but I hope you will have little difficulty understanding it.

For the most part, the vocalisations of other species are under emotional control, and serve simple signalling functions, typically in relation to activities like mating, the establishment of territory, or warnings of danger. This is true even of the chimpanzee, our nearest nonhuman relative, even though we share something like 98.6% of our DNA sequences in common.

Since the common ancestor of humans and chimpanzees walked the earth about five million years ago, which is a mere eye-blink in evolutionary time, this means that our capacity for speech must have emerged quite recently. The chimpanzee is capable of making quite a din, but there is virtually no indication that any of the cries and grunts that it utters have any of the quality of human speech. Moreover, although chimpanzees are intelligent in lots of ways, attempts to teach them to speak have been spectacularly unsuccessful.

How, then, could such a complex activity as human speech emerge, apparently out of nowhere, in such a short period of time? The problem is compounded by the fact that speech is about the most intricate skill we possess, and is arguably the key to the human mind. In trying to understand its evolution, moreover, we have very little to go on, since there is nothing like it in the communications of other animals, and very little relevant evidence from the fossil remains of early hominids. Indeed, perhaps the only sure evidence that any of our ancestors actually spoke comes from Edison's recordings a little over 100 years ago!

The apparent suddenness with which coherent speech emerged in hominid evolution has led some to argue that it was a miraculous event, a "big bang" that suddenly gave us powers of expression unknown anywhere else in the animal kingdom. Such an event is extremely unlikely, since it is in the very nature of evolutionary change that it proceeds incrementally and gradually. Even theorists like Stephen Jay Gould who argue for so-called "punctuated evolution" do not suppose that something as complex as language could have emerged as an all-or-none event.

One way round this difficulty is to suppose that language did indeed emerge quite gradually, but that it was initially dominated, not by vocalisations, but by gestures that could be comprehended visually, not acoustically. This idea was proposed as early as the 18th century by the French philosopher Etienne Condillac, and has been revived a number of times. Although it has never really caught on, I believe the arguments in its favour are now quite compelling.

Lessons from Apes

Part of the reason that chimpanzees cannot talk is that they have very poor voluntary control over vocalisation, and the shape of their vocal tracts does not allow them to create the variety of sounds necessary for speaking articulately. The mouth and throat were adapted primarily for eating and breathing, not for speaking, and it has taken quite a bit of tinkering with the basic design to enable us to speak as we do.

There is some evidence from fossil remains that the changes in the vocal tract that have made articulate speech possible were not complete until quite recently -- perhaps even as recently as 100,000 or 150,000 years ago, with the appearance of anatomically modern Homo sapiens. But although monkeys and apes have very limited control over vocalisation, they have excellent voluntary control over movements of the hands and arms, probably going back tens of millions of years. Moreover, primates are primarily visual creatures rather than auditory ones, with a capacity to perceive visual patterns that far exceeds their ability to perceive patterns of sound. Not surprisingly, then, it has proven much easier to teach chimpanzees to communicate using a form of sign language than to teach them spoken words.

The use of the hands would have been boosted when our ancestors, the early hominids, split from chimpanzee line, since the distinguishing feature of the hominids was bipedalism -- walking upright on the hind limbs. In chimpanzees and gorillas, by contrast, all four limbs make contact with the ground, with the top of the body supported by the knuckles, in a form of locomotion known as knuckle-walking. In the hominids, the upright stance would have freed the hands and arms from involvement in locomotion or balance, and enabled them to become more involved in communication.

Although chimpanzees make quite extensive use of the hands and arms in communicating with one another in the wild, we can envisage that our hominid ancestors could have greatly developed this capacity, and made extensive use of mime and gesture. It is not clear why the hominids were bipedal, but it is not inconceivable that bipedalism was selected, at least in part, because it facilitated communication in a species that was increasingly forced onto the open savannah of East Africa. This was undoubtedly a dangerous environment, populated by professional killers such as wild cats and hyenas, and effective, silent communication may have been necessary for the social co-operation necessary to ensure survival.

In some respects it is easier to imagine how language might emerge from a manual system rather than a vocal one. Most of the things we converse about belong in the world of space and time, and can be represented much more readily by using the hands and body than by using the voice. The most obvious and perhaps primitive way to represent something is simply to point at it, and pointing is something that comes naturally and early to human children. We can also mimic objects and actions with the hands and arms, so the body becomes a kind of stage where messages can be played out.

When we communicate with spoken words, by contrast, we have to develop conventions to determine which words stand for which objects, and there is nothing in the words themselves that give us a clue, except in rare onomatopoeic words like coo or buzz. In other words, gestures have an iconic quality, whereas spoken words are essentially abstract symbols. This is not to say that gestures are wholly iconic; they too would have become more abstract over time, just as many letters of the alphabet began as iconic symbols of sound (e.g., the letter o was chosen to resemble the shape of the mouth in uttering an "oh" sound, but later became more conventionalised and abstract). The point is that gestures would have provided a more "natural" form of representation to kick-start the invention of language.

Sign Language

The gestural theory has been considerably boosted by the growing realisation that the sign languages invented by the deaf are genuine languages, with true syntax and the open-ended quality that allows an unlimited number of utterances. Sign languages appear to be as "natural" as spoken language (and considerably more "natural" than written language). Deaf communities all over the world have spontaneously developed sign languages, which differ from one such community to the next. Children learning sign languages go through essentially the same stage of development as those learning vocal language, even to the point of "babbling", in the first year of life, by making repeated hand movements.

Sign languages are not confined to the deaf; they have been invented for various purposes by a number of hearing communities, including the aboriginal people of Australia and North America. Of course, we all gesture when we talk, and our gestures are intricately integrated into our speech patterns. When people are prevented from speaking, or attempt to communicate with people who speak a different language, they resort naturally to sign language. It has been observed that even blind people gesture, and even when they are talking on the phone!

Even the brain mechanisms of gesture seem to resemble those of speech. In most people, the left side of the brain is dominant for language, and this applies to both sign language and spoken language. Indeed deaf people with left-sided damage often become "aphasic", with a loss of the ability to either produce or understand sign that mimics the aphasias that occur for vocal language following left-sided damage. It has also been observed that young children learning sign language make more active use of the right than of the left hand, which is again testimony to the dominance of the left side of the brain. It is quite possible that the dominance of the left side of the brain for speech arose as a consequence of right-handedness in signing.

Although gesture still features prominently in present-day language, the sceptic may nevertheless ask why it is that we no longer use manual signs, but speak instead. If signing is so much better at communicating about a spatial world, why did we replace it with a one-dimensional medium that reduces everything to variations in time, without the spatial dimensions?

The best answer, I think, is that gesture was initially the optimal way to communicate, but as it grew more sophisticated it would have prevented us from developing other manual skills. Some writers have taken the development of stone tools, which have been dated from more than two million years ago, as evidence for the emergence of the manual skill that also underlies gestural language. But I think gestural language may have actually hindered the development of tools, which appear to have remained remarkably static for some two million years before "taking off" over the past 100,000 years. It may have been the emergence of vocal language that released the hands for the extraordinary development of manufacturing, which is still continuing at an ever-accelerating pace.

Instead of competing with manufacture, vocal language actually allows us to explain manufacturing techniques while at the same time demonstrating them. Pedagogy was born. Vocal language can also be effective in the dark, or when obstacles prevent visual access. With visual communication you actually have to look at the person delivering the message, and this requires effort; whereas you can listen to someone no matter where you are looking or no matter how you are oriented relative to the speaker.

But I do not think that language switched abruptly from hand to mouth. Rather, early communication was probably largely gestural, but punctuated with vocal grunts and cries, probably initially for emotional emphasis. But the vocal component probably became increasingly important, gradually selecting for changes in the vocal tract and the voluntary control of vocal muscles. Eventually, vocalisation took over the dominant role, with gestures then serving the subsidiary role as embellishments.

This final switch may well have heralded the emergence of our own species, Homo sapiens, some 150,000 years ago, and indeed led to the ultimate dominance of our species over other hominids. Both the Neanderthals and Homo erectus appear to have survived until perhaps 30,000 years ago, when they seem to have abruptly disappeared. Whether Homo sapiens somehow talked them out of existence, or whether the freeing of the hands from signing led to the development of more sophisticated weapons of destruction, it may well have been the switch to speech that was the determining factor.

A Just So story? Of course it is. In 1866, shortly after the publication in 1859 of Darwin's Origin of Species, the influential Linguistic Society of Paris banned all discussion of language origins, presumably because there were so many wild theories floating about. Maybe it's time to reassert that ban. But not, I hope, before you have read this.

Micheal Corballis works in the Psychology Department at the University of Auckland.