Thomas Pavel once gave a splendid paper on the changes in the presentation of human nature during the history of the novel. In the beginning, he said, characters had immortal souls, and their actions took place in a battle between good and evil for the salvation or damnation of these souls. In later sentimental novels, souls had been replaced by hearts; what mattered was romantic love, and the recognition of other selves. Later still, he said, the heart had been replaced by the psyche – a system of unconscious drives, revealed in dreams, not clear to the characters, though controlled by the author, who like the analyst, understood the forms of energy and action. Iris Murdoch felt that humans – including those of her characters who were philosophers and psychoanalysts – had not understood the shift in the moral world that had come about with the absconding of God, the vanishing of external, metaphysical moral authority. Her analysts tend to be daemonic, manipulating what she described as a “system” and a “mechanism” of sadomasochism.

The consequences of Darwin’s evolutionary idea for literature has been deeply studied. Characters in the novels I read as a girl struggled with the meaninglessness of the world – the chancy world of gradual evolution of species, and death as a final end. European novels went on using the biblical and Christian stories as paradigms long after many of the novelists had lost their belief. Forms of art change more slowly than forms of thought or belief.

Both Freud and Darwin put sexuality at the centre of human nature. In Darwin, sexual selection is one of the important ways living creatures pass on their characteristics. Freud thought all human action was driven by libido, and libido was sexual desire. The Darwinist Richard Dawkins sees all life as driven by “selfish genes”, seeking self-replication and outliving the bodies in which they are temporarily housed. In a way foreshadowing this, Freud saw what he called “the germ-cell” as immortality: the body dies, the gene lives on. Self-definition in terms purely of sexuality is one consequence of the thought patterns of the last century, and has obviously affected fictive forms; strikingly so in the works of two major American novelists, Saul Bellow and and Philip Roth.

Moses Herzog, the hero of Bellow’s Herzog (1964), is Jewish, and a scholar who studies European Romanticism. His two names, Hebrew Moses, Germanic Herzog, define him ironically as a leader of men – he cries out, from time to time, that he wanted to be a marvellous Herzog. But he is entangled in sexual disasters, cut off by successive ex-wives from his children, bodily and mentally in a mess. He writes an increasingly wild series of letters to the living and the dead, and one of the phrases that recurs is a question to Heidegger about “the fall into the Quotidian”. A fall into the quotidian – into unredeemable ordinary life – is what has happened to the marvellous Herzog, a clever idiot. He writes to an ex-tutor about the general “hatred of the present”.

"This hatred of the present has not been well-understood. Perhaps the first demand of emerging consciousness in this mass civilisation is expressive. The spirit, released from servile dumbness spits dung and howls with anguish stored during long ages. Perhaps the fish, the newt, the horrid scampering ancestral mammal find their voice and add their long experience to this cry . . . ."

But Herzog has no real means of self-expression. His world is reduced to two things – sex, and cruelty. His moment of vision comes during a chance visit to a children’s court where two ordinary stupid people (one of them, the mother, disabled) are on trial for having beaten and killed a child. Herzog imagines the child’s terrible death.

"He experienced nothing but his own human feelings, in which he found nothing of use. What if he felt moved to cry? Or pray? He pressed hand to hand. And what did he feel? Why he felt himself – his own trembling hands and eyes that stung. And what was there in modern post . . . post-Christian America to pray for? Justice – justice and mercy? And pray away the monstrousness of life, the wicked dream it was?"

Herzog ends being looked after by a mistress who is kind and beautiful and has a religion of sex which she believes can cure his ailments. The letter-writer is defeated. The human being might survive.

If Bellow is looking backwards in pain, Roth is glaring at the present. David Kepesh, the central character in The Professor of Desire (1977), teaches a class about “novels all concerned to a greater or lesser degree of obsessiveness, with erotic desire”. He wishes “to disclose the undisclosable – the story of the professor’s desire”. He makes a pilgrimage to Kafka’s grave in Prague. He is taken to meet a woman who says she is the prostitute Kafka visited. He asks questions about the writer’s sexual habits, that is, the writer’s body. He is expected to pay to see her sexual parts. This is all he finds of the tragic, witty, complex mind of Kafka: literature reduced to a gravestone and a whore, death and the body. Kepesh’s story continues in The Dying Animal (2001). He is now a famous professor and TV personality. He falls in love with Consuelo, a Cuban student with remarkably big breasts. He reflects on the wildness and personal freedoms of the 1960s, and also on an early American community, full of “riotous prodigality” “licentiousness” and “profuse excess”. He has, like Herzog’s Ramona, a kind of religion of sex – sex for pleasure, not for procreation:

"because only when you fuck is everything that you dislike in life and everything by which you are defeated in life purely, if momentarily revenged. Only then are you most cleanly alive and most cleanly yourself. It’s not the sex that’s the corruption – it's the rest. Sex isn’t just friction and shallow fun. Sex is also the revenge on death."

The title, The Dying Animal, comes from a poem by Yeats – “Sailing to Byzantium”: “Consume my soul away. Sick with desire / And fastened to a dying animal / It knows not what it is”. Yeats’s speaker has an immortal soul. The professor of desire ends watching Consuelo of the beautiful breasts, hairless after chemotherapy, preparing to go under the knife and die.

The thesis of Richard Sennett’s brilliant book The Fall of Public Man (1977) is that modern humans define themselves to themselves in terms of their private lives, and define their private lives in terms of sexuality. In the last four generations, he says,

"physical love has been redefined, from terms of eroticism to terms of sexuality. Victorian eroticism involved social relationships, sexuality involves personal identity. Eroticism meant that sexual expression transpired through actions – of choice, repression, interaction. Sexuality is not an action but a state of being, in which the physical act of love follows almost as a passive consequence, a natural result, of people feeling intimate with each other."

It is in this context that he describes a study conducted in Paris in the 1970s, which

"has shown that as people come to take their bodies as more and more complete definitions of their own sexuality, the 'symbolising' of the body becomes less and less easy for them. As sexuality becomes an absolute state fixed in the form of the body, the people who are those bodies have increasing difficulty imagining phallic forms in natural organisms such as plants or feeling a relationship between bodily movement and the activity of a cylinder or a bellows . . . . The study concludes that the result of this narcissism is a decrease in the 'metaphorical' imagination of the body, which is to say an impoverishment of the cognitive activity of creating a symbol out of a physical thing."

Someone said that the question posed by the nineteenth-century novel was “Who is the father?”. We can now, in the time of DNA analysis and fertility treatments, know who is the father, if we choose to find out, and increasingly we do. The British inventor of eugenics, Francis Galton, once said that the one right he felt every human being should have was the knowledge of his own identity (Galton was not interested in women). People in Britain obsessively research their own genealogies on the internet, and watch television shows such as Who Do You Think You Are?. At exactly the same time, we have developed medical techniques for bringing about the birth of human beings with very new forms of hereditary identities – humans born from donated eggs, donated sperm, brought up by couples, same-sex, heterosexual, to whom they may be related, or not, in all sorts of ways. What interests me, as a novelist, about all this is how such a human being constructs his or her idea of his or her identity. Such newly created kinds of humans may be happily or unhappily brought up, contented or discontented – what is certain is that they will need to define themselves to themselves in different ways from children in nineteenth-century novels: orphans or members of large families, lost heirs or illegitimate children inheriting the “sin” of their parents.

I wondered, when I first began thinking about the Selfish Gene theory, whether the interest of novelists would shift from romantic love to parental love – from the desire for the Other to the need to know and preserve and care for the genetic group to whom we belong. I have attended the Darwin seminars at the London School of Economics, and listened to passionate debates about the relative powers of Nature and Nurture in the identity of living forms, including humans. I have also listened to discussions of the origins of altruism – from the sacrifice for the good of the genetically related, to the social benefits of cooperation. All these things are full of conflicts and compromises, tragic and hopeful, in which novelists can find both imagery and stories.

The passage I quoted from Sennett deplored the increase of a narcissism which he said had caused “a decrease in the ‘metaphorical’ imagination of the body, which is to say an impoverishment of the cognitive activity of creating a symbol out of a physical thing”. Neuroscience, and the study of the activity of the brain, is beginning to bring its own illumination to our understanding of how art works, and what it is. I have come to see the delight in making connections – of which metaphor-making is one of the most intense – as perhaps the fundamental reason for art and its pleasures. Philip Davis, at Liverpool University, has been working with scientists on responses to Shakespeare’s syntax, and has found that the connecting links between neurones stay “live” – lit up for longer – after responding to Shakespeare’s words, especially his novel formations of verbs from nouns, than they do in the case of “ordinary” sentences. In Jean-Pierre Dupuy’s Aux Origines des sciences cognitives (1994; translated as The Mechanization of the Mind, 2000), an extraordinary account of the 1950s meetings of the cybernetics group which discussed minds and machines and what it was to be human, a neural network designer suggests that we delight in puns because the neurone connections become very excited by the double input associated with all the stored information for two arbitrarily connected things or ideas. It occurred to me that metaphors might arise from the same neuronal excitement – a double input, a strengthened connection (and I wrote on John Donne’s metaphorical excitement – a sensuality of the brain – in these pages, September 22, 2006).

During my lifetime we have used various metaphors for the activity of the mind – when I was a girl it was seen as a telephone exchange. Later it became fashionable to describe the brain as a computer – though a computer was constructed by a brain. In the past few years the work of Jean-Pierre Changeux has furnished us with descriptions, both purely physical and philosophically theoretical, of the way the brain puts the mind together. When he describes the relations between axons, dendrites, perception, memory, concepts and the world outside a brain, I feel I am reading a description of what I always sensed was happening, but could not describe. He is interested both in a biological and chemical “grammar” or algebra, and in the way in which things we perceive are retained – by the neurones – and combined to make “images” and “concepts” which are made by strengthened and stabilized collections of neurones, related both by the “pruning” of the sensory input and the combinations resulting from the way the mental objects are linked.

This may seem a little abstract in the context of a paper on the novel. A novel is made of language, and arouses both feelings and thoughts in its readers, as it should depict both feelings and thoughts in its people and its microcosm. Changeux’s descriptions of the cells of the brain and the way they combine and recombine give me a sense of understanding the excitement, the drive, the pleasure, I get out of making worlds with words. We have had a lot of the body as desire, and listened to many professors of desire. There is something else – the human capacity to think, and to make feelings into thoughts. It is a way out of narcissism.

A. S. Byatt’s recent books include The Little Black Book of Stories, 2003, and A Whistling Woman, 2002. She edited The Oxford Book of English Short Stories, 1998.

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