The Concept of Exaptation Between Biology and Semiotics

Introduction–A Different Point Of View In Evolutionary Biology

In 1979 the American paleontologist S. J. Gould and the American evolutionary biologist R. C. Lewontin published the article The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme. In that paper they stressed a need for change in the way of thinking about the evolutionary process and of conceiving the mechanism of natural selection as the main cause of nearly all organic forms, functions and behaviours, thus as able to forge the best among possible worlds.

The “adaptationist programme,” as they call it by referring to an account popularized by Wallace and Weismann and eventually become a core part of the Modern Synthesis or Neo-Darwinism in 1930s, generally proceeds in two step: first of all, “an organism is atomized into ‘traits’ and these traits are explained as structures optimally designed by natural selection for their functions”; secondly, when a trait is considered not as an isolated element but with reference to the whole it belongs to, “interaction is acknowledged via the dictum that an organism cannot optimize each part without imposing expenses on others. The notion of ‘trade-off’ is introduced, and organisms are interpreted as best compromises among competing demands” (Gould & Lewontin, 1979, p. 585). In a way analogue to the kind of explanations given by Dr. Pangloss, Candide’s tutor in Voltaire’s novel Candide, ou l’Optimisme (1759), for whom “our noses were made to carry spectacles, so we have spectacles”, the adaptationist programme therefore concludes that everything in an organism “plays its part and must be what it is” (Gould & Lewontin, 1979, p. 585).

Even though constraints upon the possible pathways of evolution shaped by natural selection are doubtless recognized, nevertheless they are overshadowed by “styles of argument”, namely mental attitudes constantly pushing towards the same explanatory conceptual framework: “if one adaptive argument fails, try another”; “if one adaptive argument fails, assume that another must exist; “in the absence of a good adaptive argument in the first place, attribute failure to imperfect understanding of where an organism lives and what it does”; “emphasize immediate utility and exclude other attributes of form” (Gould & Lewontin, 1979, pp. 586-587).

In order to contrast this model, on one hand Gould and Lewontin presented a “Typology of Alternatives to the Adaptationist Programme” (Gould & Lewontin, 1979, p. 590), which encompasses five different alternative evolutionary combinations with respect to the adaptive and selective nature of a peculiar trait: “no adaptation and no selection at all”; “no adaptation and no selection on the part at issue; form of the part is a correlated consequence of selection directed elsewhere”; “the decoupling of selection and adaptation” (with the two sub-cases of adaptation without selection or selection without adaptation); “adaptation and selection but no selective basis for differences among adaptations”; “adaptation and selection, but the adaptation is a secondary utilization of parts present for reasons of architecture, development or history”.

On the other hand, they claimed for a theoretical and methodological retrieval of the morphological-structural current of European biology and its approach to evolution, according to which