One of the biggest differences comes into play unnoticed. When we are born, we are no different from other primates in that we have the skill of being able to suckle and breathe at the same time, without choking to death. The young human larynx, as with that of other animals, is positioned high in the throat so that it can form a seal over the airway, permitting food and drink to pass by within its correct channel. At the age of two, however, the larynx shifts into a position exclusive to us humans, so that it ends up much lower. The interiors of our throats are now reconfigured so that, as Darwin noted, we are uniquely adapted to choking to death. What would be the evolutionary pay-off for this hazardous anatomy?
The big difference the lowered larynx makes is that we can commandeer a much fuller repertoire of non-nasal sounds by allowing the larynx to control the air exhaled, not as a steady stream, but chopped up into a series of puffs. The lowered larynx is the key to the rich range of human speech.
But is the sophistication of our communication simply due to a lowered larynx? No. It is not that apes have no language talent at all, it is just much more rudimentary. Apes can learn names for objects, even construct crude sentences: but they are nowhere near as verbally agile as us. One might dismiss the distinction as "simply" reflecting a difference in "pure" IQ. But in his recent book The Prehistory of the Mind, Steven Mithen suggests that language ability has risen as a specialised module in the repertoire of human brain power, initially as a more efficient means of social communication dating back to the time of Homo erectus some 400,000 years ago. This new module enables us to demonstrate the world around us and attempt to communicate it meaningfully. As the psychologist Herbert Terrace has pointed out, monkeys very rarely spontaneously use language in this way. Moreover, once we have taken off linguistically to construct complex sentences, we can bootstrap our brains into developing story lines, ideas that can leave the present, and concern the past or future. In this way, the physiologist William Calvin claims, we can develop far more sophisticated skills than our primate cousins.
But Mithen picks out language as facilitating an even more intriguing outcome. What I find remarkable is that Mithen is not a biologist of any hue, but an archaeologist. Hence, with the iconoclastic approach of an outsider to the brain, he comes up with a totally new idea. Once language started to be used, not just socially, but in relation to other brain modules such as technical know-how or experience of the world around one, then a mental big bang occurred - exclusive to humans - to coordinate the different abilities of our burgeoning mind. Hence the ability to interpret hoof prints, the ability to produce artifacts and the desire to communicate could all be merged into the creation of images with symbolic meaning, as a means of communication: art.
It is this ability to think metaphorically that, Mithen argues, enables us to cross mental boundaries still rigidly demar- cating the simian mind. Hence our ability to, unlike chimps, design badges of office, symbols of status, as well as jewellery adornment, and clothes made from dead animals previously classified, in the literal sense, as mere food. Perhaps, after all, we are special - not so much as naked apes, but as clothed ones.
! Susan Greenfield is a neuroscientist at the University of Oxford and Gresham Professor of Physic, London