In Zola there is the theorist and the writer, the poet, the scientist and the optimist – features that are basically joined together in his own confession of positivism; he would later in his life, when he saw his own position turning into an anachronism still style himself with irony and sadness over the lost cause as ″an old and rugged Positivist".
The poet is the artist in words whose writing, as in the racecourse scene in Nana or in the descriptions of the laundry in L'Assommoir or in many passages of La Faute de l'Abbé Mouret, Le Ventre de Paris and La Curée, vies with the colourful impressionistic techniques of Claude Monet and Pierre-Auguste Renoir. The scientist is the believer in some measure of scientific determinism – not that this, despite his own words "dépourvus de libre arbitre", need always amount to a philosophical denial of free will. The creator of "la littérature putride", a term of abuse invented by an early critic of Thérèse Raquin (a novel which predates Les Rougon-Macquart series), emphasizes the squalid aspects of the human environment and upon the seamy side of human nature.
The optimist is that other face of the scientific experimenter, the man with an unshakable belief in human progress. Zola bases his optimism on innéité and on the supposed capacity of the human race to make progress in a moral sense. Innéité is defined by Zola as that process in which "se confondent les caractères physiques et moraux des parents, sans que rien d'eux semble s'y retrouver"; it is the term used in biology to describe the process whereby the moral and temperamental dispositions of some individuals are unaffected by the hereditary transmission of genetic characteristics. Jean Macquart and Pascal Rougon are two instances of individuals liberated from the blemishes of their ancestors by the operation of the process of innéité.
Evident in Le Docteur Pascal, and again in Fécondité (which is not part of the Rougon-Macquart series), is Zola's conviction that as scientific research makes progress step by step and from generation to generation, so by slow degrees but in a similarly steadfast manner the moral progress of the human race will be achieved as the environmental faults of particular societies are swept away, as (through innéité) the hereditary failings of particular families are overcome and as on a universal scale – in novels beyond the framework of the Rougon-Macquart series – humanity unites in brotherhood.
In 1937, a well received film biography of Zola was made, The Life of Emile Zola starring Paul Muni. The film won the Best Picture Academy Award. A large part of the film details Zola's involvement in exonerating Dreyfus.