La flessibilità dell’organizzazione biologica. Strutture e funzioni alla luce di un modello gerarchico e pluralista dell’omologia

The aim of this paper is to show that the assumption of a hierarchical paradigm as regards the biological organization allows giving a new formulation to the concept of homology, and accordingly to the unity of evolution, that can be also extended to all what is not homologous. It is argued that the concepts of homology, analogy, omoplasy, convergence and parallelism do not need to be considered in terms of the opposition homology vs. analogy, omogeny vs. omoplasy, parallelism vs. convergence. Rather, such concepts point to planes and levels that are different but intersect one another in the complex world of the evolution, since the biological world itself is hierarchical, namely it is organized in various planes and levels that coexist without cancelling one another out. The evolution depends on structural constraints as well as natural selection but also on contigent and unpredictable events that are not inscribed in the ontogenetic structures and processes or in the adaptive pathway through natural selection even though they are correlated with both. From the epistemological standpoint the hierarchical view that acknowledges many biological levels has the advantage of extending the range of the concept of homology and making it more flexible. This holds for the structural and the developmental homology but also for the behavioural perspective. As the concept of homology is applied to the various levels of the biological organisation in such a way that the recognition of the homology at one level does not imply its recognition at any other level, so the concept of homology can be applied in the same way to the behaviour and its underlying structures.