Species, Variation, and Environment in Early Modern Generation Theory

Justin E H Smith (Department of Philosophy, Concordia University)

Summary

Biological species provide perhaps the clearest illustration in nature of the age-old philosophical trope of unity in multiplicity. Every member of a species is bound by similarity to every other member, while also being unlike them with respect to its particular set of variable traits. The questions as to how exactly species 'breed true', to use Aristotle's phrase, and how exactly the members of species deviate from each other in their variable traits while all sharing equally in the species, have occupied the attention of natural philosophers much longer than there has been a sophisticated science of genetics to adequately answer them.

From at least as early Hippocrates through the 17th century, a number of thinkers struggled with the phenomena of similitude and difference in biological kinds. Their investigations circled around six distinct questions. Firstly, they sought to understand how and why it is that like begets like, e.g., why it is that horses can be relied upon to beget horses, and not animals of some other species. Second, they were concerned to understand the mechanisms by which sub-groups or breeds come to share particular traits, while nonetheless also sharing equally in a larger species other members of which do not have these traits. Third, they were concerned to account for sexual dimorphism, or why it is that two individuals each of which shares equally in a species, can nonetheless differ fundamentally from one another as male and female. Fourth, they wished to know how and why, in addition to differing from other members of a species qua member of a sub-group or of one or the other sex, each individual organism also differs from every other individual with respect to the entire set of particular traits it possesses; each is as unique as a snowflake. Fifth, while the particular variable traits that make up the uniqueness of the individual organism occasionally mark the reappearance of ancestral traits, sometimes they seem to come from nowhere at all; the fact that particular variable traits may either be inherited from ancestors, or may appear evidently de novo, presented a particular challenge to thinkers seeking to understand the nature and mechanisms of the acquisition of such traits. Sixthly and lastly, early generation theorists were intent on understanding how it is that normal species reproduction --wherein like begets something not exactly like, but not altogether different- fails to occur in the case of grave birth defects or 'monstrosities'.

One important approach to the explanation of all of these phenomena appealed to entities, forces, or qualities inhering in the parental seed (whether thought to be from the mother, the father, or both) and developing or unfolding in the fetus throughout its gestation. This approach would include theories as diverse and mutually incompatible as Aristotle's explanation of reproduction in terms of an internal, immaterial, and formal principle that guides the fetus through the course of its development; the notion of seminal principles characteristic of Anaxagoras and, much later, of some corpuscularian theories such as that of Gassendi; and the doctrine of preformationism, according to which every future organism literally exists prior to its conception in the form of an ovum or a spermatozoon.

But there was another prominent line of explanation throughout the history of generation theory, which appealed to external or environmental factors, rather than internal principles of development, seeds, or primordia, to explain the diversity of species members, and sometimes their similarity as well. In this paper I will examine the parallel legacies of these two kinds of explanation in early modern generation theory, particularly in the period extending from about 1620 to 1690. But the emphasis will be placed on the latter kind of explanation, in the aim of restoring it to its rightful place as a key part of the history of embryological thought. The story of preformationism and other important developments in early modern biology has been well told. But in this story the emphasis has been consistently placed on what is internal to or contained in parents and offspring, as if organisms were conceived in the early modern period as entirely self- contained or unconstrained in their development by the world around them. While there was of course no developed concept of environment in the early modern period, much thought about the traits of organisms took them to be fundamentally world-bound entities, that is, entities that are in large part forged by external forces influencing their development.

Date: Tuesday, March 22, 2005
Time: 4:00 PM
Place: Concordia University, Loyola Campus, Science Pavilion (Building SP), 7141 Sherbrooke Street West, 3rd Floor
Room: SP 365.01
Contact: (514) 848-2424 ext 2595

Note: There are regular shuttle buses traveling between Sir George Williams Campus (1455 de Maisonneuve Blvd. W.) and Loyola Campus; see Shuttle bus schedule.


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