Una voce per un "Lessico della genetica". Generazione e aspetti dell'ereditarietà dai Presocratici a Galeno: le nozioni principali e la terminologia tecnica

This article aims at dealing with the historical development and the terminology of the notion of generation in ancient Greece, taking as well into consideration several aspects of the notion of heredity, for, at present, research in this field lacks a consistent encyclopedic entry on such subjects. The Presocratic – mainly Empedoclean – notions of ‘mixing’ and ‘separation’ lurk behind the Hippocratic treatise De genitura/De natura pueri, in which the process of generation is explained through the ‘mixing’ mechanism of a female semen and a male one. Semen comes from each part of both parents, so it is sound from the sound parts, and unhealthy from the unhealthy parts. It is considered as the “foam of blood” (Diogenes, 24 DK), gathering itself into a web of blood vessels that bring it to the genital organs. The mixed semen keeps on fixing itself in the womb thanks to pneuma (‘breath’), until the embryo takes human shape. Generation is influenced by both the environment (Airs, Waters, Places) and dietetics (On Regimen, I). Male and female are on different levels in CH, since the former is characterized as hot and strong, and the latter is considered as cold and weak; as a consequence of this, the articulation takes longer in the case of a female embryo. On the other hand, the pangenesis and the preformism theory claim for a strong mutual relatioship. Sex determination depends from the ‘prevalence’ of the male or female semen. The generation of twins of different sex depends from such ‘prevalence’, as well as from the conformation of the womb and its places (right / male, left / female). Both nature (physis) and use (nomos) have a role in the mechanism of inheritance, as the case of the Macrocephalians in Airs Waters Places shows. On the other hand, Plato’s Timaeus exemplifies the theory according to which semen derives from the spinal marrow. The structures of the body – bones, flesh, nerves – aim at protecting marrow itself for the sake of maintaining the continuity of the process of generation. For Aristotle, the female provides a specific contribution to generation, that is menstrual blood, the ‘material’ that will be fashioned into shape by the ‘principle of movement’ provided in the male semen. Menstrual blood and semen share the same nature, for they are both the ultimate secretion of nutriment, that is the residue of concocted blood. Considering the female as colder that the male, Aristotle develops the concept of the female as privation in relation to the male. The notion of ‘prevalence’ in its turn provides explanation for similarities between parents and children. The theory of a double semen originating itself in blood comes back again in Galen’s treatise On semen, which links together the hippocratic notion of a bi-sexual semen and the aristotelian one of a specific female contribution, the menstrual blood, that provides nutrition for the embryo. Furthermore, similarities between sons and mothers are considered in Definitiones medicae as the main proof of the existence of a female semen. Actually the Alexandrian physicians – Herophilus for instance – considered the female sexual organs anatomy as perfectly corresponding to the male one. As a consequence of the synthesis between the Hippocratic and the Aristotelian tradition, Galen’s embryological doctrines were very long-lasting in medical thought.