CHAPTER 1. THE ARISTOTELIAN LEGACY: ANIMALS AS FORM-MATTER COMPOUNDS; REPRODUCTION AS TRANSMISSION OF FORM
It will be a central argument of this book that, overall, the place occupied by biology in Leibniz’s philosophy is closer to the one it enjoys in Aristotle than in Descartes: it is a field of application par excellence of general philosophical principles, rather than an obstacle to the viability of these principles. In this and the following chapter, we will focus on the contrast between Aristotle and Descartes, and then move on to position Leibniz in relation to them.
In this chapter, we will gain a thorough understanding of Aristotle’s approach to both general and developmental physiology, and will then move on to his account of sexual reproduction. We will conclude with an account of the central Aristotelian doctrine according to which ‘like begets like,’ that is, of his generation-based theory of species membership. Throughout, we will be concerned to position Aristotle’s account of animal motion, development, and generation in a way that will highlight its sharp differences with Descartes’s later account, in order ultimately to show the brilliant manner in which Leibniz will synthesize elements from both of these systems of biology.
In the first section, on organic structure and function in Aristotle, we will consider Aristotle’s account of the ontological priority of functions over the bodily organs through which these functions are executed, taking as our example his analysis of vision and the eye. This analysis will provide us with a first instance of the general principle that also underlies Aristotle’s account of sexual generation: that of the priority of form over matter. In Aristotle’s theory of reproduction, the father imposes both a formal and final cause, through the vehicle of the semen, upon the material of the mother’s uterus. This brings about what Jim Lennox has called “formal replication,” in which the father ensures his own eternity in kind, as Aristotle puts it, if not in number. While the product of generation is not an exact copy of the father, it is the closest thing possible to this, and the extent to which it falls short of this mark is traceable in large part to the degrading influence of the mother. The menstrual blood possesses in potentia all of the possible qualities of a human being that may be actualized once the blood is acted upon by the semen; but still the menses are not pure seed, “for it lacks one thing only, the source of the soul” (GA II 3 737a). This soul source is at the same time the source of (to speak anachronistically) the blueprint or program that determines how the fetus will develop. The semen determines the end toward which the fetus will develop, since, in Aristotle’s view, in natural beings such as animals the formal and final causes are one and the same. For Aristotle, a woman is a degradation of man, “a male deformed.” A female is generated when the movements introduced by the male’s semen prove to be weak, and are consequently overcome by the movements of the menstrual blood. Monstrosities occur, finally, when the movements of both of these are very weak and lack even the efficacy to render the menstrual blood into a distinct particular human, leaving it instead at the level of development common to all animals in general (GA IV 3). If no degradation were to occur, the male would reproduce itself perfectly. This can never happen, since particular primary substances are not eternal. The particular mechanism by which perfect self-reproduction is hindered is the mutual interaction of the movements of the semen and the menstrual blood at conception. Thus there is no need to explain where defective fetuses come from. They are merely privations of form, which manifest themselves as recapitulations, not of earlier evolutionary stages, as some modern theories would later hold, but of a more general category --animal-- to which particular members of any animal species belong.
Aristotle’s account of species membership, then, is intimately linked with his account of sexual generation: to be a member of a certain biological kind is just to have one’s form originally transmitted by one’s male progenitor, ‘for like begets like’. As we will see, this is a very convenient principle to uphold within the context of a hylomorphic metaphysics, but its truth, and even its comprehensibility, become severely problematic with the rise of mechanistic biology.