The evolution of the curve

Technology and economics have their part to play in our perception and enjoyment of curves. The Detroit car industry started to do those lascivious organic shapes - the fins, the snouts, the blisters and the brows - only when steel became available in strips wide enough to accommodate imaginative sculptural effects. Hitherto, narrow-strip steel had limited the expressive range of the mass-production stylist to a boxy repertoire.

No car manufacturer has a better record in the matter of manufacturing voluptuous, curvaceous forms than Coventry's Jaguar. The 1961 E-type, a bravura exercise in phallomorphic style and the first production car to join the collection of New York's Museum of Modern Art, where its feline beauty makes the fine art sculpture of the Sixties look ham-fisted, had just a single straight line: the chromium-plated bar that divided the ovoid air intake. Interestingly, the E-Type's ravishing profile was determined by a slide rule in the hands of Jaguar's aerodynamicist, Malcolm Sayer.

The 1968 Jaguar XJ6 was a car of astonishing elegance. A signature of the Jaguar style was the glorious detail of the sculpted eyebrows above the headlights; the care and patience required both to design and to manufacture these subtle but psychologically significant details helped to lend the whole car a keen sense of class, of design in depth, of lapidary strength. But there was a price to pay. The XJ6's vast bonnet was made of 17 separate pieces of steel, was filled with lead, and had to be finished off by a man in a leather apron wielding a file.

Such charming archaic practices could not survive in a harsher economic environment. The successor to the XJ6 was the XJ40. As a tribute to rationalisation this car had a bonnet fabricated from only two metal components, but the sculpted eyebrows were a victim of the same cost-cutting. The press tool technology of 1987 did not allow such formal extravagance. As a result, the XJ40 was cheaper to manufacture; but, lacking the signature curves, and with a leading edge of the bonnet resolved by a banal straight line, it became the most characterless Jaguar ever made.

Consequently, in his recent makeover of the car, Jaguar's design director, Geoff Lawson, restored the eyebrows and recaptured what he calls the marque's "DNA", which expresses itself in "surfaces with a lot of visual activity". A jury of Milanese designers recently noticed this visual activity and voted the Jaguar the most beautiful car in the world. I suspect those precious eyebrows were crucial.

The way curves are used in vehicle design is a black art. Technocrats argue for the primacy of aerodynamics in shaping cars, but even the stern verities of drag, lift and penetration allow a lot of scope for variation and caprice. After all, if aerodynamics were an exact science, planes would all look the same. They don't.

Even in the days of powerful computer assistance, establishing the shape of a car is a process of trial and error, a result of well exercised intuition and an educated eye. It is not a purely scientific exercise. The semantics of shape may be mysterious, but there is no gainsaying their effective power.

Getting a curve just right speaks volumes about what a car means. Uwe Bahnsen, the designer of the Ford Sierra, once explained to me that Mercedes- Benz uses the same gauge of metal as other manufacturers, but is careful to bend it only to radii which give an imposing impression of strength. There's no such thing as frivolous rococo for the austere Benz.

Inevitably, natural metaphors invade any discourse about curves. You hear a lot about osmosis, flesh, muscle and phallus when you talk to designers. Luigi Colani, an experimental German-domiciled Italian designer, responsible for France's first glass fibre car, says: "There are no straight lines in the universe."

Lawson explains: "The difference between a curve that is muscular and one that is anorexic is about 3mm."

Myself, I have always believed that BMWs achieve their presence (and their grip on the collective imagination and cupidity of the middle classes) because they combine an athletic, masculine bulk and stance with feminine details and lines.

There are fat rounded cars and thin rounded cars. The way the result is determined remains a matter of discretion and taste. Lawson says: "We spend a lot of time in the studio accelerating the parabola." While he has access to enough computer power to simulate the Gulf War, the way Lawson works remains typical of the motor industry: the shape of cars is still determined by artistic principles, not microprocessors. They continue to sculpt life-size lumps of clay and decide on where the flat curves go by laying tape on the model. The success of a three-dimensional radius is determined by shining lights and making an aesthetic judgement. In this way Lawson hopes to make the new Jaguar S-Type the "optimum expression of steel". You can judge for yourself at the Motor Show.

We are in a historical period when curves dominate vehicle and product design. Twenty years after Luigi Colani first developed biomorphic prosthetic extensions for Canon (which went into production as the sinister, but ergonomic, EOS) every manufacturer now makes cameras which look as if they have come out of the Mekon's toolshed. A design tradition that started with a Box Brownie has matured into a specialised activity of astonishing sculptural audacity and positively fetishistic detail. It is not that curves are more articulate than straight lines, just that they communicate a different set of values: intuitive, secure, humane and natural, as opposed to rational, nervous, mechanical and artificial.

In some historical periods, the tastes co-exist. Rudolf Steiner established the successful cult of theosophy. His enthusiasm for Goethe's scientific writings (he published them as Goethes Naturwissenschaftliche Schriften in 1926) was given architectural form in Eric Mendelssohn's extraordinary Goetheanum at Dornach. This irrational, curvaceous building was the perfect architectural expression of a belief system based on speculative mysticism. But at Walter Gropius's hilariously humourless Bauhaus, the philosophy of design-for-mass-production had to be expressed in severely technocratic straight lines, right angles and plane surfaces.

Since Cassirer's Idee und Gestalt was published in 1921, philosophers have tried to understand the precise aesthetic effect of curves, although it is tempting to say that the current taste - which is typified by such objects as the Olympus centurion, the Apple iMac, the Fiat Seicento and the new Jaguar - may be a comforting reaction to millennarian angst.

While you could stretch a point and say that the highly complex surfaces of the new Ford Focus may be an illustration of fractals which signify the influence of chaos theory in contemporary life, the fundamental attraction of curves depends on biomorphic factors.

Curves suggest the familiar comforts of nature. A drop of water naturally forms into a curvaceous teardrop, not an angular pyramid. Natural materials tend to erode into curves. Luigi Colani says: "Nature is still the best designer I know. Just look on an egg. Is its shell not a fantastic thing?"

Ever since the infamous jelly mould, culinary metaphors have had an unfortunate reputation in car design, and it will be a long time before anybody admits to having been directly inspired by an egg, but the new Fiat Seicento has as many interesting curves as two dozen free-range. As the direct successor to the 1992 Cinquecento (from which it evolved) the hugely cute Seicento proves the rule of curves in current design: the Cinquecento was emphatically linear, even boxy, in design, but although it retains the same proportions, the designers have missed no opportunity to create curves on the Seicento.

While the old car had a thin slot for an air intake, the new one has a gaping banana. The rear-view mirrors are elliptical, the steering-wheel boss is shaped like a rugby ball, and the rear glass is an indescribable shape whose southern perimeter is described by an audacious and unusual droop. Inside, "instrument panel" is a ridiculously inappropriate term to describe a complicated and intelligently irrational compilation of scoops, hyperbolae, sines and ellipses. With this garrulous language of curves, Fiat's designers emphatically state: a modern car.

Curves define the modern sensibility and - in the case of Ford, Fiat, Apple, Olympus and Canon - suggest a way of reconciling advanced technology with nature, at least in symbolic terms. But where exactly does inspiration come from? Geoff Lawson has a Fender Stratocaster on his wall, and a finer set of industrial curves you will not find. Luigi Colani, on the other hand, gets it from looking down a microscope.

When Kalil Gibran wrote: "I discovered the secret of the sea in meditation upon a dewdrop", he did not imagine that he was writing the manifesto of millennial design.