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Andrea Ceccon


Andrea Ceccon works on the representations of biological variation in the history of the life sciences through the prism of the notion of polymorphism, roughly from the second half of the nineteenth century to the first half of the twentieth.

In defining what polymorphism is, we can refer to what was long considered its ‘standard’ notion in some important biological fields – that is, the definition provided by E. B. Ford during the 1940s. Ford described polymorphism as “the occurrence together in the same habitat of two of more discontinuous forms, or phases, of a species in such proportions that the rarest of them cannot be maintained merely by recurrent mutation”. This definition aimed at demarcating polymorphism as a specific phenomenon distinct from what historically had been described in the more general terms of ‘variation’ and to bring it into the framework of genetics, thus framing it in the form of ‘genetic polymorphism’.

However, in current bio-medical research, polymorphism is generally described in a very different perspective - that is, by means of of single base-pair variations in the DNA of individuals, or single nucleotide polymorphisms (SNPs). What we could call ‘the Ford vision’ of polymorphism and the contemporary one that emerged with protein and DNA sequencing techniques draw on two different understandings of identity and difference. The former considers biological species as genetically uniform entities that are kept as such by natural selection; the latter considers biological species as harbouring a large amount of variation. The first vision tends to highlight the fact that that variations between populations are negligible, the second highlights the fact that variation within species is relevant and both visions imply one same desideratum – founding ethical considerations on scientific ground. However, the outlined strategies are almost diametrically opposed to one another.

With these considerations in view, the aim of my project is to provide a historical analysis of the changes of the notion of polymorphism. In fact, polymorphism has been always used as a proxy for what can be counted 'difference' and 'sameness', but it has always been itself a multifarious concept, as well as an implicit one. It has been used as a specific description of ‘difference’ within species from the middle of the 18th century but it did not act as a stable category; on the contrary, several biologists tried to reshape its meaning on the basis of their theoretical needs or day-to-day practice, opening up alternative ways of thinking about the relation of living forms.

The aim of the research is to analyse how this instable notion helped to recast the more general concepts of ‘variability’ and ‘variation’ from the middle of 19th century, when the general acceptance of the Darwinian theory of evolution raised new interest in the study of variation, to the 1960s, when molecular biology has been used to determine polymorphism at the level of proteins and DNA. Part of this analysis will be carried out by analyzing how diagrammatic representations have been used to reduce the complexity of the cases under investigation, thereby producing and integrating knowledge about relations of similarity, affinity, and descent among organisms by hiding certain aspects that, in theory, could have been taken into account, by considering only the selected information that is deemed useful for obtaining the desired outcome and by bringing together data that otherwise would have been scattered.