Nachtomy & Smith: o vivo e o não-vivo

What those who adhere to the conceptual distinctness of the domain of living beings tend to highlight are a few remarkable features of these beings that seem entirely resistant to explanation “in the same manner as the rest.” For one thing, these beings seem to be structured entirely unlike anything else in nature. They have complex interworking parts (as, admittedly, do certain other natural but plainly inanimate systems), and moreover this functional complexity seems to operate at very fine-grained levels of analysis. Indeed, prior to the discovery of the living cell in the 19th century, and to some extent even up until the DNA sequencing of a number of biological species, it could easily appear that there simply was no lower limit to vital organization at all (i.e., that the functional complexity would continue beyond any possible level of analysis). In this respect, living beings seemed to be in a class entirely apart from other natural entities, which, it was supposed, could be analyzed down to their basic, nonfunctional constituents in a small number of steps.

A second apparent difference between living beings and nonliving entities is that the former seem to operate according to special laws that have no equivalent in the rest of the natural world. For example, if a nerve is pricked, and the limb of which it is a part twitches, this twitch cannot be understood in any obvious way according to the same principles that explain the communication of motion from one billiard ball to another. Now of course those who deny that life constitutes a distinct ontological category can argue that, at the microscopic level, what is going on is fundamentally no different than what goes on with billiard balls, that muscle contraction and expansion involve countless, sub-visible billiard-ball-like collisions. But the onus is on them to find these collisions and to describe them, and in the absence of any plausible means of providing such a description, those who defended the ontological distinctness of living beings not surprisingly were not impressed by the evident explanatory stretching required to extend the language of mechanical physics to the domain of physiology. Similar points may be made, of course, about other peculiar physiological phenomena, such as digestion, respiration, circulation, etc. But one phenomenon has always stood out as a particularly salient motivation for claiming that living beings constitute a distinct ontological class: namely, their capacity for reproduction, for cycling back upon themselves, as Aristotle   would put it, thus obtaining a sort of eternity in number if not in kind. Now today we are starting to see some rudimentary examples of machine self-replication, but in the 17th century, it seemed a fairly solid and certain shibboleth for the separation of the living from the nonliving, or of beings from machines and artifacts, that whereas no two clocks placed in a room together ever managed to produce a third, little clock, two dogs or humans, if appropriately selected, very well might. Asexual generation was already well attested (though differently described), and spontaneous generation was still debated; these do not involve the coming together of two individuals for the production of a third, but they do seem to be processes that have no analog in nonliving nature. Spontaneous and asexual generation, along with sexual generation, all seem to yield up beings in the strict sense, rather than simply yielding new arrangements of preexisting matter, as would seem to be the case in, say, the formation of stalactites or (a more controversial, indeed borderline, case) crystals. Th is is to say that living beings, in contrast to natural entities, are the sort of things that are generated rather than simply formed, and what generation is, exactly, and how it is that a being that previously did not exist, later does, is not just a philosophical problem, but at least since the pre-Socratics   has stood as a philosophical problem par excellence.

One further way in which living nature stands apart—and also a way that, in turn, stands apart from those already listed—is in respect of its order and variety, and the nature of the kinds of living things that make up this variety. Of course, there are chemical and physical kinds too, but as many early modern philosophers insisted, it is living kinds, what we now call biological species, that seem to represent the very idea of what would later be called, aft er J. S. Mill, ‘natural kinds.’ Biological species, in the early modern period as today, seem to play an important role in constituting our idea of what it is for a thing to be a thing of a certain sort: A moment’s reflection will convince you that the great majority of examples typically adduced by philosophers to illustrate the idea of form, essence, haecceity, and so on, have always been biological species. Th is means, inevitably, that thinking about the living world entered in important ways into classical philosophical debates, such as that between the nominalists and the realists, and it would be neglectful to gloss over the way in which biological species imposed their particular character here, or to suppose that the examples of, say, ‘cowhood’ and ‘triangularity’ always served the same conceptual purposes, in the same way, in the course of philosophical arguments about whether there are real kinds or not. In the early modern period in particular, the longstanding practice of allowing biological species to stand in as paradigmatic examples of kinds in general was thrown into a sort of crisis, as the rate of discovery of new kinds sky-rocketed as a consequence of microscopic investigations, as a result of greatly increased contact with the non-European world. Empirical discoveries greatly complexified the understanding of natural order, and indeed called into question the very idea that nature constitutes an order at all.