The Reith Lectures 1994: Monstrous Mothers: Marina Warner is this year's Reith lecturer. Her six lectures, which are called 'Managing Monsters', explore how myths express and shape our attitudes. Here is the first in the series

In 1852, at Sydenham in south London, Queen Victoria opened the first dinosaur theme park. She presided over the unveiling of 29 full-scale models made by Benjamin Waterhouse Hawkins, who was the draughtsman Darwin himself had employed to depict the animals he found on his voyage in the Beagle. The word dinosaur - dread lizard - had been coined in 1841 by the leading palaeontologist of the time, Richard Owen, and Hawkins made his dinosaurs to Owen's state-of-the-art specifications.

They're still there. Spick-and-span signs in gold and scarlet paint direct visitors to the 'Farmyard', 'Boats', and 'Monsters'. Monsters, not dinosaurs: the distinction between natural history and myth wasn't drawn then. There, on an island in a lake, crouching under mixed plantings of large trees, the concrete creatures come into view: the pterodactyl spreads its wings like a large heron, the snout of the mosasaurus emerges from the water like the toothy maw of Jonah's whale in a medieval illumination; ichthyosaurus, with daisywheel eyes, seems to waddle on fins as comfortably as a walrus. Their inertia in the suburban London park is pastoral, reassuring: dinosaurs spending the afternoon at their club in St James's.

A hundred and forty years on, in a much more famous park, the dinosaurs are living, moving, crying, talking - almost. The simulations and models in Jurassic Park give a glow of genuine wonder to the film. They represent rather a change from the lumbering dinosaurs of Crystal Palace Park at Sydenham. Dinosaurs, even when called monsters, seemed benign then, but today they've become cunning, voracious, nippy - and female.

CLIP FROM JURASSIC PARK:

Scientist 1: We bred eight originally, but when she came in, she took over the pride and killed all the others. That one - when she looks at you, you can see she's working things out. That's why we have to feed them like this - she had them all attacking the fences when the feeders came.

Scientist 2: The fences are electrified though, right?

Scientist 1: That's right, but they never attack the same place twice. They were testing the fences for weaknesses - systematically. They remember.

Scientist 2: You know what this is? It's a dinosaur egg. The dinosaurs are breeding.

Child: But Grandpa said all the dinosaurs were girls

Voracious, cunning girls. Lethal - and fertile, as well. Michael Crichton's clever plot, for all its air of scientific fidelity, reveals vividly the presence of myth today.

Female organisms in the film prove ultimately uncontrollably fertile, resistant to all the constraints of the men of power. The story can be reduced to a naked confrontation between nature, coded female, with culture, coded male: the bristling, towering, jagged, megavolt fence can't hold the force of the primeval at a stage of intelligent evolution: velociraptors collaborate on the kill - one as decoy, one as executioner - and want nothing more than to snack on human flesh.

Is the terror the velociraptors inspire in any way connected with their femaleness? It isn't emphasised as such - though the book calls the park a matriarchy. Popular films of this kind often refract widespread concerns in metaphorical terms, and then reinforce them. And no director of the contemporary cinema rivals Steven Spielberg's ability to touch a common chord. The accelerating pace of change since the Fifties has magnified the influence, the power, and the dissemination of myths; as human ingenuity leads to scientific breakthroughs which offer salvation and, at the same time, destruction, as strains on the family grow, the imagination hunts for stories to explain the pervasive malaise. One of the stories in mass circulation today is a very old one, but it's taken on new vigour: women in general are out of control,

and feminism in particular is to blame. It has become a bogy, a whipping boy, routinely produced to explain all social ills.

The she-monster's hardly a new phenomenon. Greek myth alone offers a host - of Ceres, Harpies, Sirens, Moirae. Associated with fate and death in various ways, they move swiftly, sometimes on wings; birds of prey are their closest kin - the Greeks didn't know about dinosaurs. Ungoverned energy in the female always raises the issue of motherhood; fear that the natural bond excludes men and eludes their control courses through ancient myth, which applies various remedies. In Aeschylus's Oresteia, when Orestes has murdered his mother Clytemnestra, the matriarchal Furies want justice against the matricide - but they find themselves confronting a new order - led by the god Apollo. Orestes is declared innocent, and in a famous resolution which still has power to shock audiences today, the god decrees:

The mother of what's called her offspring's no parent

but only the nurse to the seed that's implanted.

The mounter, the male's the only true parent.

She harbours the bloodshoot, unless some god blasts it.

The womb of the woman's a convenient transit.

In this brutal act of legislation, the god of harmony declares that henceforward, in civilised society, only the father counts. The mother's nothing more than an incubator.

The spectre of gynocracy, of rule by women, stalks through the founding myths of our culture: both Theseus and Hercules fight with the Amazons - and vanquish their queens. The Amazon's separatist queendom made them tantalising but also monstrous in the eyes of the Greeks; the terrible massacres of their army depicted on stone reliefs and vases redounded to the fame of the Greek heroes as surely as cutting off Medusa's head.

In the folklore of the past, classical and medieval, the female beast, like the velociraptor, was also sometimes cunning and purposely concealed her true nature: the Sirens lured men with their deceitful songs, and later tempted fierce anchorites in the desert, approaching St Anthony for instance, with honeyed words, hiding their diabolical nether parts under sumptuous dresses. Male beasts, as in Beauty and the Beast, or male devils, as in the temptations of St Anthony, don't possess the same degree of duplicity; you can tell you're dealing with the devil on the whole, but when evil comes in female guise, you have to beware: the fairy queen may turn to dust in your arms, and poisonous dust at that. This is a trope that sends thrills through stories as disparate as Wagner's Tannhuser, in which the knight loses his soul to the carnal goddess of the Venusberg, and Rider Haggard's She, where, as you might remember from the film, Ursula Andress cracks open like a speeded-up earthquake and reveals beneath the image of loveliness, nothing but a crumbling hag. But none of these dissembling serpents and she-monsters can compare with the vision of Lamia in Keats's gorgeous romance noir:

She was a gordian shape of dazzling hue

Vermilion-spotted, golden, green, and blue;

Striped like a zebra, freckled like a pard,

Eyed like a peacock, and all crimson-barred;

And full of silver moons, that, as she breathed,

Dissolved, or brighter shone, or interwreathed

Their lustres with the gloomier tapestries

She seemed, at once, some penanced lady elf,

Some demon's mistress, or the demon's self

Her head was a serpent, but ah, bitter-sweet]

She had a woman's mouth, with all its pearls complete

Her throat was serpent, but the words she spake

Came, as through bubbling honey, for Love's sake.

But when Lamia woos Lycius, she doesn't, of course, reveal her snaky shape and nature. Only at the last minute, at the wedding feast, she's unmasked. 'And with a frightful scream she vanish'd' - while the poor bridegroom expires in a swoon.

Such fairy wives don't only make a pretence of being women; they also contradict all ideas of proper womanly conduct. Of the throng of mythical and monstrous enchantresses, one of the most famous and most fascinating of all is still Medea.

Medea embodies extreme female aberration, from the tragedy by Euripides in the fifth century BC to the fictional translation of the story in Toni Morrison's recent masterpiece, Beloved. It's through Medea's sorcery that Jason wins the Golden Fleece: she lulls the snake, its guardian, with a potion obtained from Hecate, Queen of the Night. But she also uses her magic powers to cheat her father, boil an enemy in oil, cut her brother into pieces, and, when Jason has abandoned her, to murder her own children by him.

Euripides dramatised with powerful empathy Medea's tragedy: when Jason decides to take another wife more useful to his current ambitions, Medea, who had betrayed and killed so much on his behalf, turns on those she loves in revenge. Her maternity is the terrain of her authority, or rather of the authority left to her. And so she strikes at Jason where he is most vulnerable, and where his reach - and all men's - is weakest. Among bad mothers of fantasy she is the worst; as such she speaks to our times, when the bad mother is always present as an issue, as a threat, as an excuse, as a pleasurable self-justification and as a political argument. Women still use, and abuse, the authority they are allowed as mothers, because it is what they have, or, as in Medea's case, what they have left.

Euripides's tragedy introduced Medea the child-killer, and has made this side of her much more familiar than other texts, which stress her enchantments and, in some cases, her humanity. Medea the child murderer contravenes the most fundamental criterion of femininity - maternal love. She shares this with many fantasies of female evil: the inquisition condemned witches for cannibal feasts on children; in Judaic myth, the succubus Lilith was believed to haunt cradles of new-born infants to carry them off, and the classical Lamia was a child-stealer as well as a bloodsucker. Amulets against these harmful powers were worn in medieval Europe; Satanic cults today are held to practise the same gory rites. Myths of female aberration predispose the mind to believe in these monstrous crimes; but the same myths have also stirred resistance. In 1405, the poet and historian Christine de Pisan, a young widowed single mother, and one of the earliest women to support her family by writing, compiled a riposte to the circulating tittle tattle about women, in her Book of the City of Ladies.

She sets up an array of heroines, geniuses, leaders, and saints, and portrays them building a heavenly city. Among the paragons, without turning a hair, she included Medea: 'Medea was very beautiful, with a noble and upright heart and a pleasant face.'

Later, in a passage on the dangers of love, Pisan relates that Medea unfortunately fell in love with Jason, and listened to her passion, only to find that he abandoned her. This turned her 'despondent', writes Pisan. Again, no memory of the remarkable form Medea's despondency took.

When I first read this, nearly 20 years ago, I thought Pisan was absurdly coy, and felt that feminism could not proceed without facing women's crimes as well as their wrongs - the ills they did as well as those done to them. This is still my position - when it comes to historical events; but with regard to myths which shape thought and action - and history - the question becomes much more complicated. Every telling of a myth is a part of that myth: there is no Ur-version, no authentic prototype, no true account. Pisan's Medea is as mythically true as Euripides's Medea; Pisan is important because she's one of the first women writers to tell stories against the grain of tradition. Hers might tend to whitewash; but the tradition she inaugurated tends more to accept, even revel in the darkness.

The mythical she-monster's allure spellbound Sylvia Plath, for instance, who in the Ariel poems often contemplates atrocity with narcissistic pleasure. Many other writers and artists and performers today have also moved on to enemy territory where Medea and other monsters are pacing.

Ironies, subversion, inversion, pastiche, masquerade, appropriation - all the post-modern strategies of the last two decades are buckling under the weight of culpability the myth has entrenched. It permeates the furious response, for instance, to the increasing numbers of single mothers. Instead of inquiring into the causes of marriage breakdown, into the background to so many fatherless families, into the reasons women have become heads of households, instead of attending to the needs of women who are raising children on their own and recognising the way the work of care still stitches together the torn fabric of society, lone mothers have come under prolonged and continuing attack. Newspapers, television programmes, the Cabinet, let fly with one accusation after another: one scare story after another. Home alone children of single, working mothers, home alone children of lesbian couples, opportunistic teenage deviants, welfare swindlers, or at least leeches, are spawning child murderers, breeding monsters.

A myth is a kind of story told in public, which people pass on to one another. Myths wear an air of ancient wisdom, but that is part of their seductive charm. Not all antiques are better than a modern design - especially if they're needed in ordinary, daily use. Myths offer a lens which can be used to see human identity in its social and cultural context - they can lock us up in stock reactions, bigotry and fear, but they're not immutable, and by unpicking them, the stories can lead to others. Managing monsters means preventing them from managing us. Myths convey values and expectations which are always evolving, always in the process of being formed, but - and this is fortunate - never set so hard they cannot be changed again, and newly told stories can be more helpful than repeating old ones.

As a footnote to this look at the serpentine metamorphoses of the monstrous female, I'd like to direct your notice to some scientific data about the praying mantis.

'Eckehard Liske and W Jackson Davis of Santa Cruz, California videotaped the mantises' courtship while the insects thought they were in private and found a pleasant ritual dance in place of cannibalism - and with both partners surviving. The researchers say that until now scientists have distracted the insects by their presence and by watching them under bright lights - and that they didn't give them enough to eat.'

This most loved creature in the surrealist bestiary of misogynist folklore, this insect famous for devouring her mate alive after mating, has been vindicated. Let them alone, give them enough to eat and look] They fall into peaceful, mutual, post-coital slumber.

This is an edited version of last night's talk, which will be repeated at 9.50pm this Saturday on Radio 3. The lectures will be published on Thursdays in the 'Independent'.

(Photograph omitted)