We experience the world through a particular kind of body that has been evolving for a long, long time. In countless ways, culture - which often begins with an imaginative response to nature - reflects our animal heritage. Even a glance at the cultural history of the face reflects its natural history. Unlike the hairy mugs of other mammals, the naked faces of our clan - the higher primates and Homo sapiens - reveal every flicker of emotion. Hairy-faced Chewbacca in Star Wars has recourse to only a few expressions. However, in the Planet of the Apes movies, especially in Tim Burton's 2001 remake, the naked faces of the ape characters approximate the nuances of simian expression. The charming animals in the film Babe never quite achieve convincing lip movements. Much more persuasive are the orang-utan and chimpanzees in the sequel, Babe: pig in the city, because their lips bear a family resemblance to our own.
This biological legacy explains why a dubbed film can be even more distracting to follow than a subtitled one. For countless millennia, we have been watching lips move during speech. The human imagination has even promoted the natural attributes of our mobile primate lips to a cultural level by inventing ventriloquism. Like shaving the head, ventriloquism responds to the body by removing a prominent trait - lip movements, which normally synchronise with the voice - and thereby accentuating it. In an ironic gesture, Charlie McCarthy, the wise-guy ventriloquist's dummy who sat on Edgar Bergen's lap, often turned his head to look up at Bergen and accuse him of moving his lips.
We apply our imagination to the body from top to bottom. When Francois Boucher composed an entire painting around the curvaceous nude posterior of Mlle O'Murphy, he was responding to a unique attribute of Homo sapiens. So were Correggio and Raphael when they painted the classical trio of The Three Graces, at least one of whom usually reveals her attributes from behind. Thanks to the gluteus maximus, the heaviest muscle on the human body, we are the only ape to have a prominently curved and muscular derriere. Other apes may share our naked faces, grasping hands and shifting loyalties, but only we can wear a thong bikini. These curves result from the particular muscular arrangement required to stand upright and propel the bipedal body forward. It is to this evolutionary milestone that Alejandro Escovedo aims the double entendre in his song "Castanets": "I like her better when she walks away . . ."
Naturally, our clever forepaws have also been invested with symbolic meanings. The hands that politicians clasp after signing treaties, the clenched fists depicted on political posters, evolved from the grasping adaptations of our simian ancestors. When we apply eyeliner, shake Martinis, or gesture meaningfully during rush hour, we employ the same machinery as a chimpanzee dipping a twig into a termite mound. The unique aspects of our opposable thumbs are demonstrated in the film of The English Patient: when Willem Dafoe's character loses his thumbs to Nazi torturers, his hands are reduced to mere flippers. In contrast, Uma Thurman's gigantic thumbs in Even Cowgirls Get the Blues qualify her to become a world-class hitch-hiker.
The influence of hands on their supposed master is a common theme in the arts. The notion that they might even act independently appears in surprising places. In Bill Watterson's comic strip Calvin and Hobbes, the father tires of always reading the same bedtime story and devises one about a renegade hand that could be anywhere. Suddenly he grabs his own throat and pretends to throttle himself - at which point Calvin faints. In Thomas Burke's classic 1930s crime story "The Hands of Mr Ottermole", our primate hands become murderously insubordinate. The villain hates his own hands: "Have you thought of the sickening potentialities that lie within the scope of that five-tentacled member?" It is so easy to see this part of the body as a separate entity that in the Addams Family television series and films there is a character who consists entirely of a single animated hand.
Like our speechless primate cousins, we groom ourselves and each other. No other part of the body can be modified so quickly and painlessly as our mammalian fur, and this flexibility is still a godsend for a fickle herd animal such as ourselves. Malcolm X knew this when he gave himself his first conk, and he proved it again when he denounced such straightened hair as an Uncle Tom curtsy to white society.
Our ambivalent relationship with hair as a potent symbol has been simmering for millennia. Why did Samson and other ancient heroes come to embody a link between long hair and strength? In a world attuned to natural properties this association requires no great leap of the imagination; it is simply an exaggeration of genuine attributes. Hair grows as if it has a life of its own. It can be separated from the body without harming its owner. And, being composed of keratin, the same decay-resistant protein found in our fingernails and the horn of the rhinoceros, hair seems to outlive the mouldering body. As a consequence, the ancient Franks believed that the very health of a society could be linked to its leader's hair. Their kings wore long, flowing locks to symbolise potency.
During the Second World War, most new arrivals at Nazi concentration camps were forced to have their heads shaved. More important than any pretence of hygiene was the emblem of subjugation. The same was true in Jamaica in the late 1960s, when police symbolically tamed Rastafarians by publicly cutting off their untamed locks. After 11 September, investigators found a document instructing the terrorists to prepare themselves for their holy self-sacrifice by shaving "excess hair from the body". If our animal nature can be purified by trimming our animal signifiers, then the opposite must also be true. Such symbolism explains the appeal of that ambivalent superhero Wolverine, hairily embodied by Hugh Jackman in this year's sequel to X-Men.
In 1969, Nik Cohn remarked that the Rolling Stones intended their then-unconventional hairstyles "as a kick in the teeth, as insult and ridicule heaped on every drabness of the system; hair as symbolic of sex, of energy; hair almost as religion". No image from the 1960s better demonstrates hair as such a symbol than Bradbury Thompson's poster Flower Child (1967). A young woman stares challengingly at the viewer. Had we evolved from reptiles or birds, the features peering at us would be very different. But instead the face - naked and surrounded by hair - reflects our history as vertebrates, mammals and primates. The woman's wavy yellow-green-brown locks tangle and burgeon until they fill the picture, finally becoming indistinguishable from vines and grass, until you cannot tell at what point the unruly sprawl of nature turns into a human being.
The human brain is just as much a product of evolution as the body that houses it. One of its natural functions is to sort information into explanatory narratives. Nowhere is this urge more apparent than in the brain's creative response to the body that carries it around. Hands take on lives of their own. Voices speak behind still lips. Hair becomes a link to the earth itself. Despite hard-headed scientific efforts to stick to the facts, we keep promoting the mundane experiences of bodily life to a higher symbolic level.
Michael Sims's book Adam's Navel: a natural and cultural history of the human body is published by Allen Lane, the Penguin Press (£12.99) on 1 August