On my way to the Future Entertainment Show at Olympia last year, I found I was the only woman waiting for the Tube. The station was unusually full for the middle of the morning, with scattered groups of young men in jeans and trainers, gaggles of young boys and, with some of the boys, their fathers. When the train came and the carriage doors opened, a rather dazed looking pigeon fluttered out. A man near me laughed. 'Don't worry,' he said, 'it's only a virtual reality pigeon.'

I streamed in to the show with the crowd, clutching my razzle-dazzle, hi-tech, impossible-to-forge ticket, and plunged into the roaring hall. The video games industry has grown in value from almost nothing to pounds 700m over the past four years, and on multiple screens the season's new offerings in interactive play and 3-D simulation were being triggered by the very latest in ergonomic joypads to keep bleeping, scrolling, beaming up, blasting, crashing, bursting into flames and starting up again. I was not the only woman any longer: there were one or two grannies, one or two mums. And the marketing staff on the stalls were almost all women - known as 'skirt power' in the trade.

In the 'chill-out zone' in the gallery, at stands and on platforms, the players at the banked consoles of games were chasing monsters, zapping and slicing and chopping and head-butting and dragon- punching. Popular culture now teems with visible, almost palpable, monsters, with robots, cyborgs and aliens, with fiends, mutants, vampires and replicants. Millennial turmoil, the disintegration of so many familiar political blocs and the appearance of new national borders, ferocious civil wars, global catastrophes from famine to Aids, threats of ecological disasters, of another Chernobyl, of larger holes in the ozone layer - all these dangers feed fantasies of the monstrous. At the same time, scientific achievements in genetics, reproduction, cosmetic surgery and transplants have raised tough and unresolved ethical anxieties about the manufacture of new beings. These are reflected in myths that exist at every level of our culture.

Myths and monsters have been interspliced since the earliest extant poetry from Sumer: the one often features the other. The word myth, from the Greek, means a form of speech; while the word monster is derived, in the opinion of one Latin grammarian, from monestrum, via moneo, and encloses the notions of advising, of reminding, above all of warning. But moneo, in the word monstrum has come under the influence of the Latin monstrare, to show, and the combination neatly characterises the form of speech that myth often takes: a myth shows something, it issues a warning, it gives an account which advises and tells, often by bringing into play showings of fantastical shape and invention - monsters. Myths define enemies and aliens and in conjuring them up they say who we are and what we want. They tell stories to impose structure and order. Like fiction, they can tell the truth even while they are making it all up.

The appearance of monsters is intrinsic to at least one kind of fundamental mythological story, the story of origins. Dragons, serpents and beasts multiply in the genealogies of the gods and the origins of the created world (even the Bible's monotheism allows glimpses of the leviathan and the behemoth). Dragons linger on from the cosmologies of the Babylonians and Assyrians. The presence of monsters marks the beginning of nations, of cities - think of St George and the dragon; of Cadmus, who sowed the dragon's teeth to build and people Thebes.

In Antwerp, in the 16th century, the city fathers were still showing distinguished visitors the bones of Druon Antigoon, the giant who had been slain by the first king of the region, Brabo, friend and relation of Julius Caesar. The gargantuan shoulder blade and magnificent rib actually belonged to a sperm whale but they served very well to represent the vanquishing of the brute and the coming of civilisation to Antwerp.

Chaos threatens in various forms: the hero Bellerophon, for example, was able to subdue the she-monster Chimera by flying down on the winged horse Pegasus and piercing her in her fiery gullet. The flames melted his spear tip and she choked to death as the lead cooled inside her. Chimera's name came to mean illusion: the ultimate monster of monsters, who is both frighteningly there and yet a spectre, who shows something real that at the same time exists only in the mind.

Reason can be awake and beget monsters. Extreme, fantastical, and insubstantial as they are, they materialise real desires and fears, they embody meaning at a deeper, psychic level. We are living in a new age of faith of sorts, of myth-making, of monsters, of chimeras. And these chimeras define human identity and especially the role of men.

Mary Shelley's novel Frankenstein, published in 1818, has become the contemporary parable of perverted science, but this reading overlooks the author's more urgent message. She grasped the likelihood that a man might make a monster in his own image and then prove incapable of taking responsibility for him. When the creature at last confronts Victor Frankenstein, the creator who has shunned him, he beseeches him, using 'thou', the archaic address of intimacy:

'I am thy creature, and I will be even mild and docile to my natural lord and that which thou owest me. Oh, Frankenstein, be not equitable to every other and trample upon me alone, to whom thy justice, and even thy clemency and affection, is most due. Remember I am thy creature; I ought to be thy Adam, but I am rather the fallen angel, whom thou drivest from joy for no misdeed. Everywhere I see bliss, from which I alone am irrevocably excluded. I was benevolent and good; misery made me a fiend. Make me happy and I shall again be virtuous.'

'Begone] I will not hear you. There can be no community between you and me; we are enemies. Begone, or let us try our strength in a fight, in which one must fall.'

Victor Frankenstein rejects and wants to destroy the being he has generated from his own intelligence and imagination; he can only flee, and then, when confronted, offer mortal combat - in the desire to be the victor, as his name suggests. The book offers a dazzling allegory of monsters' double presence: at one level they are emanations of ourselves, but at another, they are perceived as alien, abominable and separate so that we can deny them, and zap them into oblivion at the touch of a button.

But monsters in the new, nightmare pandemonium of popular culture have something in common which distinguishes them in a crucial way from the ancient Hydra or Medusa or Chimera: they do not emanate from nature but are either men, or man- made. Frankenstein's creature is their immediate ancestor in this, too, but Shelley does not set up a superior warrior figure to vanquish her monster. Her novel pleads on the creature's behalf: he is capable of goodness if Frankenstein would only love him and teach him and include him, not abandon him to his pariah state. The remedy for Frankenstein's hubris does not lie in destroying the monster; Shelley writes explicitly against dealing with evil by heroic, lethal exploits. Implicitly, she is recasting the monster in the image of his creator, as Adam was of God: the creature issues from Frankenstein as his brainchild who is also his double, who acts to define him. Frankenstein's instant, murderous hostility to his creation may resonate with some of Mary Shelley's own disillusion with her father and her husband and their revolutionary ambitions. It may reflect her feelings about male and female antagonisms. But its mainspring is located in her hero's self-loathing. Her extraordinary and brilliant book inaugurates a new breed of monster, who is not ultimately alien, but my brother, my self.

When popular myths place characters such as Slugathon or Robocop centre stage, and then annihilate them, they are conjuring up the perverted products of human intelligence. And unlike Mary Shelley's book, these plot lines almost invariably reject science's offspring and propose the enemy monster's defeat through force. Nobody in this kind of story sits down to learn to talk, as Frankenstein's creature does so poignantly and so elaborately when he eavesdrops on the English lessons given in the woodland cottge by the old man and his family to the beautiful Arabian fugitive Safie.

Current tales of conflict and extermination never hear the monster say: 'I am malicious, because I am miserable' or 'Make me happy, and I shall again be virtuous.' It sounds absurd to expect them to, because we are so accustomed to expect the hero to have no other way of managing the monsters than by slaying them.

Monsters who manifest their nature, like Frankenstein's creature, clearly present easier targets than those in disguise. Deception is a theme that runs through the history of fantasy art, which itself constitutes an attempt to deceive. It achieves a brilliant apotheosis with the replicants of Blade Runner, in Ridley Scott's cult movie. Replicants are androids, impervious, almost invulnerable; however, they look like humans and have been artificially provided with childhood memories and they do not know that they are monsters. As the word android implies, they are men - and yet not men at the same time. This is the ultimate, representative nightmare of this fin de siecle; 150-odd years ago, Frankenstein's creature suffered because he knew his own deformity. Jekyll and Hyde knew each other well, though the evil Hyde, as his name tells us, was already concealed within Jekyll. This is still optimistic stuff compared to Blade Runner. The film - and the book - touch a live contemporary nerve when they imagine that the robotic monsters look just like humans, that their nature is not apparent - either to us or to them.

The acute, painful problem today is that these manufactured monsters are ourselves; and ourselves especially as the male of the species. A recent shift in ways of telling an old, widely distributed legend illustrates rather well the new fascination and unease surrounding men: in this urban myth, a woman living alone hears a strange sound coming from her kitchen, and sees a hand coming through an opening sawn in the door. She lays her poker in the fire and when it is glowing, attacks the intruder, who instantly withdraws with a howl of pain. The next day the woman meets the child of her neighbours, who tells her that her father has gone to hospital with a terrible burn on his hand. In the old version, the intruder was a witch; but she has turned into a man, an ordinary family man, a neighbour who - and this is crucial - doesn't look dangerous.

Fear of men has grown alongside belief that aggression - including sexual violence - inevitably defines the character of the young male. Another myth shadows the contemporary concept of male nature: the intruder could be a rapist. Alongside the warrior, the figure of the sex criminal has dug deep roots in the cultural formation of masculinity. The kids who kill a series of ghouls or aliens can tell themselves they are not like the monsters they are killing. But the serial killer - the very term is of recent coinage - has a human face like theirs. He has dominated contemporary folklore, a figure of thrill and dread, for 100 years, since the terror of Jack the Ripper gripped the Victorians, to the present-day murderers who are now interviewed on television from prison.

Films - and the books on which they are based - often mete out punishment to sexual women, in the same way as spectators of the Ripper's victims in the London Dungeon enjoy the horror even as they shudder at it. But video games are more scrupulous about current taboos: most of their heroes cannot be seen to attack and murder women as such - with the result that women have pretty much disappeared from the plots. There is the occasional dewy-eyed girl hoodlum or pixie- haired hell-raiser or salacious spider woman and there are some female street fighters - all active, assertive types and good examples of how positive imaging can backfire. And the stock motif of the damsel in distress recurs. But the effect of the almost total absence of women from this all-engulfing imaginary world of boys is to intensify the sense of apartness, of alienation, of the deep oppositeness of the female sex.

Modern myths still approach the enigma of sexual difference using very old and simple formulae - and if the girls are getting tough, the tough are getting tougher. In this emphasis on warrior strength, the new stories conform to very ancient ones, stories which were grounded in the different social circumstances of a military, or pastoral and archaic society - the heroes of Greece, the samurai of Japan. Slaying monsters, controlling women, still offers a warrant for the emerging hero's heroic character; this feeds the definition of him as a man. But this narrative is so threadbare, it has come away from the studs that held it to the inner stuff of experience: warrior fantasies today offer a quick rush of compensatory power, but pass on no survival skills - either for a working or a family life.

When the young Achilles is hidden by his mother in women's clothes, because she knows from an oracle that he is to die in the Trojan war, it proves child's play to winkle him out. Odysseus disguises himself as a merchant and goes to the court of Lycomedes, among whose daughters Achilles has been concealed. Odysseus produces a chestful of gifts overflowing with jewels and trinkets and textiles - and weapons. The king's daughters bedeck themselves, of course, but Achilles girds himself over his frock with sword and buckler and is thus unmasked and carried off to win the war for the Greeks. Baroque paintings exist of the warrior revealed, grasping his weapon while the girls primp; and the subject inspired a baroque tragi-comic opera. .

But the mighty Greek heroes are not the only models of the male. Achilles might choose a mighty sword and buckler, and Hercules use muscle power and a big stick. In the fairy-tale tradition, by contrast, heroes live by their wits. In the Arabian Nights a poor fisherman finds a bottle in his nets and when he opens it a huge angry ogre of a genie rises up and threatens the man with instant death. The fisherman responds by saying that he cannot believe that anyone so awesome and so magnificent could ever have fitted into such a little bottle, and he begs the genie to show him how he did it. The genie obliges and gradually winds himself into the vessel, whereupon the fisherman jumps on it and stoppers it in a trice. He then refuses to let the genie out again until he has granted him fabulous riches.

Charlie Chaplin and even Woody Allen have worked this groove, the heroic pathetic. The gleeful use of cunning and high spirits against brute force, the reliance on subterfuge, have almost faded from heroic myths told today. But in the prevailing popular concept of masculinity, as reflected in comics, rock bands, street fashion and Clint Eastwood or Arnold Schwarzenegger movies, the little man, the riddler or trickster, has yielded before the warrior hero, the paradigm of the fittest survivor.

Cunning intelligence has been superseded by force as the wellspring of male authority, of power; in today's morality, force even feels somehow cleaner, purer, more upright. The very word 'wily', the very idea of subterfuge, carry a stain of dishonour. Boys are not raised to be cozeners or tricksters; they are brought up to play with Action Man and his heavy-duty, futuristic Star Wars arsenal, to identify with the Ninja Turtles as crusaders, vigilantes, warriors on behalf of the planet.

I am not advocating the conman over the soldier or the cozener over the honest gentleman. That would be be absurd. I am observing a trend towards defining male identity and gender through visible, physical, sexualised signs of potency rather than through verbal, mental agility.

Mythical heroes such as Oedipus, Jason and Orestes serve as tragic warnings; their pride, their knowing and unknowing crimes, the matricides and infanticides, self-blindings and suicides, all the strife and horror they undergo and perpetrate, did not make them exemplary, but cautionary. They provoked terror and pity, not emulation. The tragedies they inspired offered their heroes as objects of debate, not models. No one, having seen Oedipus at Colonus, would feel he wanted to be Oedipus in the way that watching a spaghetti Western excites hero worship for Clint Eastwood.

But in the arenas of contemporary culture - the television channel, the computer game, the toy shop, the street - traditional mythic figures of masculinity like the warrior and the rapist circulate and recirculate every day, setting up models, not counter-examples; and the forms which convey them do not contain argument or counter-argument, as in a Greek tragedy, but reiterate the message as in an advertisement. They are appealing to the group's purchasing power, shaping tastes, playing on rivalry and vulnerability. They do not cry 'Beware', rather 'Aspire]'

Boys will be boys, people say, when they mean aggression, violence, noise, guns. But does the warrior ethic fit the needs of our civil society? Why does an age which believes in medical and scientific intervention on an heroic scale, which works for change - and delivers it - co-exist with a determinist philosophy about human nature and gender? The point about Frankenstein assembling the monster from body parts haunts contemporary consciousness, but the book's main philosophical argument - that his viciousness is learnt, not innate - is somehow overlooked. The biological and genetic revolution already upon us can alter and save bodies, but stories which feature such bodies assume that their natures are static, determined, doomed. Rare is the character in a video game or comic strip who develops or learns to be different. Yet anthropology has shown that, in the territory of sexuality as well as other human areas, social expectation affects character. Masculinity varies from group to group, from place to place, and its varieties are inculcated, not naturally so.

Societies which expect boys to be unflinching warriors subject them to rituals of traumatic severity in order to harden them. Among the Sambia in New Guinea, a tribe in which men are warriors and nothing else, and women are feared and despised, boys are removed into exclusive male control around the age of six, and begin the series of violent initiations which will turn them into men like their fathers. Proper, cultural masculinity does not come naturally, it seems, to the men in such a tribe. Why should it to a child living in London or Aberdeen?

When the Serbian-Montenegrin forces in the current war in the Balkans cursed the women they raped and told them they would bear children who would forever be their enemies, they were speaking from a society of ferocious adherence to military values, paternal lineage and a cult of male heroism.

I am not offering an excuse, a rationale, or adequate explanation of men's capacity to rape and kill. But I am rejecting the universalising argument about male nature that the rapes committed in former Yugoslavia are committed simply because men are rapists. In the words of an American rights lawyer, Catherine McKinnon, 'men do in war what they do in peace, only more so' and 'similar acts are common everywhere in peacetime and are widely understood as sex'. These sweeping assertions work against mobilising change; they present as sovereign truth beyond history, beyond society, the idea that the swagger and the cudgel come naturally to men due to their testosterone, a hormone that, according to this view, is always in excess. The Serbian rapist becomes the summation of male nature.

The problem of how to make men without turning out killers and rapists has inspired a men's movement in America which is enjoying huge international success, led by its guru, the poet Robert Bly. Bly rightly notices that women are unhappy about men, that this does not make men happy either, and that the absence of fathers is keenly mourned. Feminism has taught women vibrancy and knowledge, he argues, and masculinity must follow its example. Bly advocates the appointment of surrogate fathers - men who take younger men under their protection. He writes admiringly of tribal rites of passage in which men are socialised in this way, alluding to shared blood-letting among the Kikuyu and other symbolic woundings. Though Bly does not actually advocate direct bodily assault, the men's movement has adapted many of the socialising methods used by tribes like the New Guinea Sambia: separation from women in male bonding weekends, or homoerotic physical contact - though so far none of the men's groups has started practising ritual fellatio of men by boys, as the Sambia do in order to transmit the necessary semen for manhood from generation to generation.

It seems to me that Bly has framed his cure the wrong way round: the monsters of machismo are created in societies where men and women are already too far separated by sexual fear and loathing, segregated by contempt for the prescribed domestic realm of the female, and above all by exaggerated insistence on aggression as the defining characteristic of heroism and power.

The presence of fathers will only reduce the threatening character of maleness if sexual polarities are lessened, not increased. Delinquency among young men has recently provoked acute alarm - one man in three in Britain will have been convicted of a crime by the age of 30. And it is carelessly repeated that single mothers are specially to blame.

But it is interesting to look at the problem of fatherless boys from another angle. Boys brought up by their mothers alone, the popular argument goes, compensate through violence for the lack of a strong male role model in their lives, they express the anger they feel at the sole female authority at home. This could be put the other way round: the culture that produces irresponsible fathers openly extols a form of masculinity opposed to continuity, care, connection, negotiation and even cunning - qualities necessary to make lasting attachments between men and children, men and women. These boys are not deprived of strong masculine role models, they are not in rebellion, but are suffering from the compulsion to conform.

In Mary Shelley's later, apocalyptic novel, significantly called The Last Man, the hero exclaims: 'This, I thought, is power] Not to be strong of limb, hard of heart, ferocious and daring; but kind, compassionate and soft.'

It is a measure of the depth of our present failure of nerve that these words sound ridiculous, embarrassing, inappropriate; that this cry strikes one as a heap of hooey, a foolish dream, a chimera. Shelley's utopianism is too ardent for our cynical times. But we can take away from her work the crucial knowledge that monsters are made, not given. And if monsters are made, not given, they can be unmade, too.

This is an edited version of last night's talk, which will be repeated at 10.30pm this Saturday on Radio 3. The third lecture, 'Little angels, little devils: keeping childhood innocent' will be broadcast on Wednesday 9 February on Radio 4 at 8.45pm and will appear in the Independent the following day.

(Photographs omitted)