Later, Zola’s solidarity would become overtly political, with his famous ‘J’Accuse’ pamphlet during the Dreyfus case, in which he showed that political idealism was by no means incompatible with a deep and often pessimistic understanding of reality. Zola was also a materialist in the specific sense that he believed that what happened in the world was explicable by means of that world. This does not, as we have seen, prevent him from bringing his novels to melodramatic and symbolic climaxes—on the contrary, it suggests that these great melodramatic denouements, for all their excess, are firmly fixed in causes and effects that are rooted in sturdy plotting.

Zola had, as a young writer, written poetry of a romantic and idealistic bent, but quickly turned his back on it in favour of a more documentary and socially committed literature. This commitment was never, in the novels at least, jeopardized by sentimentality, and this in part is what caused many of his critics to impute a bleak and amoral vision to his Rougon-Macquart series. Zola could be doctrinaire about his method and his subjects, and gathered around him a group of disciples who took him as leader of the ‘Naturalist school’ and met at his house in Médan. In 1880, Zola and a handful of fellow Naturalists produced the volume Médan Nights (Les Soirées de Médan), showcasing short stories by six writers: Zola himself, J.-K. Huysmans, Maupassant, Henri Céard, Léon Hennique, and Paul Alexis. The book’s great success was Maupassant’s ‘Boule de Suif’, and it is revealing that, of the writers represented, Maupassant quickly moved away from the group and refused to be circumscribed by an ‘–ism’, Huysmans was leaning in the direction that would lead, four years later, to the decadent mystical masterpiece Against Nature, and Céard, Hennique, and Alexis, who stayed true to the Naturalist ethos, are now forgotten. If there is a moral to this story, it is that writers must either create their own movements, their own ‘–isms’, or write their way beyond them. Zola defined the Naturalist style, but was not confined by it.

As well as Taine, who straddled the border between literature and social sciences, Zola was deeply influenced by more specialized scientific and medical theory, especially in his earliest work, such as Thérèse Raquin and the first Rougon-Macquart novels. He claimed to have based his writing method on Claude Bernard’s Introduction to the Study of Experimental Medicine (1865), and the idea of an ‘experiment’, in which the novelist arranges his materials and equipment like a scientist and observes the results of the experiment objectively in order to discover a principle or a set of laws from it, is key to Zola’s method.

Theories of heredity provide ways of talking about history and tradition, as well as medical or biological questions. The nineteenth century was a period obsessed with narratives of heredity in the widest sense: the relationship of the present to the past, the extent to which, politically, socially, intellectually, we are condemned by or chained to our pasts, able to build on them, or escape them altogether. It is not only individuals and families who must contend with what they inherit, but whole societies with their political and economic systems, their sense of nationhood, their literature, and their science. But it does not take long for a new scientific explanation to become, in its turn, another myth, and the upsurge in late nineteenth-century writing of literature that drew on medicine is evidence of this: it was not just Zola and the Naturalists who turned to medicine, but Decadent and Symbolist poets, who begin peppering their verses with words like ‘hysteria’, ‘neurosis’, ‘neurasthenia’, and other terms from medical glossaries, often improperly understood or used only for their shock value. The extent to which apparently opposing schools of literature shared—admittedly with different aims and results—a fascination with the language and models of heredity, biology, medicine, and pathology, is something that has not been sufficiently explored, but which Zola himself was fully aware of. These are not overarching theories which explain Zola’s beliefs or contain his fiction but simply ideas of his time, to which he turned, in which he delved, which he selected and shaped and fictionalized. Does Zola submit his fiction to these ‘scientific’ principles, or does he submit the science to the principles of fiction? Every reader will have their opinion, but the fact that his novels can be read and felt and understood without any reference to the theories that went into them suggests the latter.

Biological heredity gives Zola not just the material with which to create and propel characters but the framework with which to plan a cycle of novels, to think on a scale few novelists manage. It is worth casting ahead to the last novel in Zola’s Rougon-Macquart cycle, Doctor Pascal, where the grandson of Adelaïde Fouque, Pascal Rougon (brother of Marthe and Eugène Rougon) a doctor in Plassans for thirty years, catalogues his own family’s heredity in order to develop a serum that will cure nervous and hereditary diseases. In this novel, Dr Pascal may be seen as analogous to the novelist himself: a fearless researcher into the ills of the family (and by extension, society), but also part of it, caught up in and also the product of that family (and, also by extension, that society). Zola writes that, of all Félicité’s children, he is the one who ‘did not seem to belong to the family’, and adds, in such a way as to leave the character some leeway to escape the Rougons’ fate, that he is ‘one of those frequent exceptions to the laws of heredity’. Pascal, whom we first meet in The Fortune of the Rougons, is devoted not to money or power (much to his mother’s bafflement and his brothers’ consternation) but to science: ‘He had a particular passion for physiology. It was known in the town that he often bought dead bodies from the hospice gravedigger, which made him an object of horror to delicate ladies and certain timid gentlemen. [. . .] For two or three years, he had been studying the great problem of heredity, comparing the human and animal species with each other’ (ch. 2). Pascal’s methods are scientific, but his aim is idealistic: to free himself and them through knowledge and understanding. In this, he perhaps resembles Zola himself. The serum, which is a piece of almost Balzacian supernaturalism, and so clearly unbelievable that we must take it symbolically, is best interpreted as truth itself. Zola’s style has changed a great deal in the nearly twenty-five years between the first Rougon-Macquart novel and Doctor Pascal—it has become softer and more optimistic, more overtly symbolic and idealistic—but the cycle has returned to Plassans, where, despite the novel’s own tragedy, the ending is a hopeful one.