It is significant that from early on in his writing career, Galdós was very consciously exploring evolutionary theory for literary purposes. This certainly does not preclude that at other times evolutionary theory finds its way into Galdós's creativity, subconsciously or indirectly; certainly at times attempting to gauge the source of an idea may be as impossible (and unnecessary) for the reader as indeed it would have been for the author. In Galdós’s quest to create a Spanish novel worthy of comparison with the very best of the nineteenth-century European novel elsewhere, he made a point of working from within the Spanish tradition as he saw it. He developed the costumbrista social types which relied upon the biological science of the late eighteenth and early nineteenth centuries, into social species whose behaviours reflected the evolutionary theories of the second half of the nineteenth century. Evolutionary science provided Galdós with a template of mutability denied to his costumbrista forebears, and this aided his expansion of their original ideas into more prolonged and complex texts. The species element in Galdós's writing poses questions as to the nature not just of the individual within society, but also of individuality itself. The acceptance and imposition of labels and therefore roles implies a certain level of determinism in Galdós's social portraits. However, Galdós never allows himself to be blocked off into the ‘one way street’ of biological determinism. On the contrary, he might well have agreed with Stephen Jay Gould when he states, ‘Our genetic makeup permits a wide range of behaviours – from Ebenezer Scrooge before to Ebenezer Scrooge after’ (Gould 1979, p. 266). A refusal to accept one’s place in the pecking order, accompanied by attempts to challenge it or to ‘fast-track’ it will usually be doomed to failure. Isidora Rufete wants to take up her ‘rightful’ position in Madrid's social zoo, but cannot recognise her real relationship to it, through failure to accept her origins and all that these imply. On the other hand, Fortunata's Lamarckian transformations are, in a gradual and periodic fashion, achieved – social evolution is a series of small leaps for her – a pattern which paradoxically falls into broad agreement with the social gradualism expressed by the narrator of her story. The birth of Juan Evaristo even carries us beyond Lamarck: it represents a small yet significant leap in the evolution of the social classes.