Beatrice Busi | The crisis of binary sex model in contemporary biology


Although the sexual difference is often assumed to be absolute and to be an invariant biological entity, it is, indeed, a working concept variously described, represented and interpreted with regard to - and sometimes in spite of – current experimental data and research methods.
On one hand, the binary model of sexual difference, in the history of twentieth-century biology, was an “epistemological obstacle” to the wider understanding of sexual differentiation processes and of the unpredictable divergence between determination laws and differentiation effects; yet, on the other hand, the same history is punctuated by meaningful discontinuities.
Scientific controversies therefore are an excellent vantage point to analyze how the success of binary model is socially and historically affected not only by “pre-scientific ideas” about gender but also by epistemological approaches. Examples are the radical criticisms promoted in 30’s and 40’s by biochemists of Amsterdam School to sexual hormones classification system; spectrum sexual model put forward by the “heretic” genetist Richard Goldschmidt’s; and Tracy Morton Sonneborn’s challenge to the transfer of male-female classification in the study of protozoan reproduction.
All these researches, though developed in different frameworks, exhibit some key common features, emphasizing the complexity of biological functions and the developmental and differentiation aspects of sex, rather than inheritance laws. This research approach is less prone to reductionist temptation and, probably for this reason, it has promoted a radical questioning of the binary model.
The very distinction between determination and differentiation underwent a gradual hardening, first along with the success of the Mendelian genetics research program on chromosomes of the Morgan's school, and later with the success of the central dogma of molecular biology. Genetic determination assumed a normative hierarchical value, leading to the marginalization of studies on the differentiation processes.
Only at the end of the century, with the renaissance of developmental biology and the emergence of epigenetic research, determination and differentiation reached a new balance.
In recent decades, the reduction of biological sex to the binary model met again with new difficulties emerged from the new molecular studies aimed  at the understanding of intersexuality. The outcomes of these researches have determined an eclipse of the “testocentric” model - developed in the 50’s and culminated in the 90’s with the discovery of SRY gene -, while promoting a new conceptualisation of the biological relationship between male and female.
In the biological epistemology, therefore, the crisis of the binary model has assumed the pattern of "historical recursion", where "repetition" continuously produces new "differences."