Teenage superheroes come in all varieties. Some, like Clark Kent in Smallville, were born super. Some, like Harry Potter at Hogwarts Academy, must graft their way to superiority. The rest, like Buffy the Vampire-Slayer when she became the Chosen One and Peter Parker after his fateful meeting with a genetically modified spider, have superiority unexpectedly thrust upon them.

One might expect superheroes of the last kind to find it hard to adjust, but sudden transformation is a commonplace of teenage experience. The worst existential difficulty that will afflict them as they grow older is the necessity of living in the world of series melodrama. As their adventures multiply, the inexorable process of melodramatic inflation will force their adversaries to become weirder, more destructively ambitious, and far more ingenious in finding terrible ways to place them in mortal danger.

This process is evident in the history of superheroism. Comic-book superheroes are direct descendants of the superheroes who featured in the American pulp magazines of the 1930s, but evolution has given them greater powers and gaudier plumage. Superman, the Man of Steel, is a linear descendant of Doc Savage, the Man of Bronze. As a technologically sophisticated haunter of the dark, Batman is an extrapolation of The Shadow. Spider-Man is a modernized version of The Spider, whose main claim to fame was that he was even more screwed-up than all the other secret-identity-nursing masked vigilantes commissioned to thwart the terrorist activities of criminal masterminds during the Great Depression.

Spider-Man has been hyped as the first conspicuously post-September 11 superhero movie, but September 11s have always been routine business for American superheroes. The January 1935 issue of The Spider pitted the eponymous hero against 'The City Destroyer'; the story's blurb, juxtaposed with a picture of a crumbling skyscraper, began: "Thousands of busy persons bent over their desks in the tallest building in the world - conducting the commerce of the nation - when suddenly the steel girders began to creak and twist, and the gigantic edifice swayed giddily in the wind....". Unfettered by the Comic Book Code, the Spider - who usually contented himself with burning a spidery brand into the foreheads of his deserving victims after shooting them dead with his twin Magnum 45s - eventually trapped the skyscraper-felling Murder Master in a tank full of acid, reassuring himself while listening to the felon's screams of agony that: "It was horrible... but it was necessary, and it was just. God knows it was just!"

When this melodramatic tradition is traced back to its origins in the French roman feuilleton, we find that it was the supervillains rather than their law-abiding adversaries who initially bagged the titles and cultivated the big reputations. The unsung pioneer of melodramatic crime fiction was Paul Féval, who was a prolific inventor of criminal secret societies run by exotic and charismatic masterminds between 1843, when 'Les Gentilhommes de la Nuit' featured in Les Mystères de Londres, and 1875, when the eighth and last novel chronicling the evil exploits of 'Les Habits Noirs' appeared. The English 'penny dreadful' serials that ran in parallel to the early romans feuilletons in the 1840s produced Varney the Vampyre, Wagner the Wehr-Wolf and, in The String of Pearls, Sweeney Todd, the Demon Barber of Fleet Street, but not a single hero whose name became legend.

When Catwoman's ultimate ancestress, La Vampire, hit Paris in a Féval serial published in 1855 (but set in 1804) the main opposition to the eponymous femme fatale was provided by the seemingly- unassuming Jean-Pierre Sévérin, the keeper of the Paris Morgue. But Jean-Pierre only needed a broken fishing rod in his hand and a change of stance to be revealed as master swordsman Gâteloup, the ultimate ancestor of all dual-personality superheroes.

The mysterious masked swordsman in the scarlet caped suit who had earlier featured in Féval's Le Fils du diable (1846) was only able to appear in several places at once because there were three of him, and nobody cared who they were when not in costume. But they provided the model for America's first caped crusader, Johnston McCulley's Zorro. By the time Zorro arrived on the scene, though, charismatic villains had enjoyed half a century of hero-eclipsing celebrity.

The fact that superheroism had evolved as a belated response to escalating supervillainy was carefully noted by the first philosophical advocate of superheroism, Friedrich Nietzsche, who wisely advised the would-be übermensch that: "Whoever fights monsters should see to it that in the process he does not become a monster."

In the game of melodrama, it is villains who define the moral magnitude of the tasks facing heroes, thus licensing the lengths to which they may go in heroic opposition; by threatening and perpetrating horrors, villains invite the visitation of similar horrors upon themselves. Any hero who responds wholeheartedly to such an invitation runs the risk of becoming more and more like his adversaries as his career progresses.

The dangers of superheroism evolving to mirror supervillainy are compounded by an opposite process. The alchemy of melodrama often makes extravagant villainy look suspiciously like heroism, as William Blake observed when commenting that Milton was "of the Devil's party without knowing it". Morally disreputable characters like Rocambole and Fantômas became the stars of ever-extending series of 19th-century romans feuilletons, plotting a course subsequently followed by the likes of Fu Manchu and Count Dracula.

The modern glut of school-set fantasies in which the problems of adolescence are modelled in the imaginative clay of horror movies began in 1957 with I was a Teenage Werewolf and was cleverly sophisticated in the 1970s by Stephen King and Brian de Palma in Carrie. In stories of this kind, victims freed from their inhibitions and given the power to strike back become monsters with whom it is perilously easy to sympathise. In both the Buffy the Vampire-Slayer and Harry Potter series, to name two prominent recent examples, it is often extremely difficulty to figure out which of the seemingly good guys is actually bad, and vice versa.

Given that superheroes are mere phantoms of melodrama, produced by taking poetic justice to outlandish extremes, it may seem that none of this matters very much in the real world. As Oscar Wilde pointed out, however, life imitates art more often and more assiduously than art imitates life. Spider-Man was allegedly delayed in production by the necessity of removing a scene in which Spider-Man strung a web between the Twin Towers, whose actual destruction generated exactly the kind of horror that provided the imaginative fuel of 'The City Destroyer'.

No superheroes are available to hunt down the Murder Master responsible for the authentic atrocity, but there is a superstate, which must formulate its own response - and whose collective conscience must decide what is ultimately to take the place of The Spider's lethal tank full of acid.

Although few contemporary Americans are likely to take much inspiration from Nietzsche, no matter how apt his observations may have been, they do have other models of superheroism available than spectacular deliveries of retributive justice. The Crash Test Dummies suggested in their debut single Superman's Song (1991) that it was actually Clark Kent, not Superman, who was the real hero, because - even though nobody could stop him from simply taking anything he wanted - he put his suit and glasses on, got a job and earned his daily crust just like any ordinarily virtuous person.

Bearing in mind that movie superheroes actually have triple identities, we can take a further step behind this particular example. Nobody could think of Christopher Reeve as an authentic superhero when, having made his own giant leap to superstardom, he allowed his Superman to dump Lois Lane because poor Margo Kidder had grown a little older between movies. But who can doubt that he is an authentic superhero now, when he requires courage and endurance even to draw breath, and pours millions into research into technologies that might one day restore to him, and many others, the ability to put on their suits and glasses and go to work?

While planning the further development of their superheroic careers, Peter Parker and his audience might do well to consider these issues, no matter what plans Hollywood may have for Spider-Man's next adversary.