Notes on the Metaphysics of Life
The following notes are adapted from David Oderberg’s excellent book, Real Essentialism:
1) The Aristotelian-Thomistic tradition (hereafter “A-T”) provides the resources for a metaphysical defense of the maxim omne vivum ex vivo: “all life [is] from life.” According to A-T there is a difference in kind, and not merely in degree, between living substances and non-living substances — that is to say, there are features that belong to the essence of living things that are wholly absent in non-living things. Moreover, according to the scholastic principle of proportionate causality, a cause cannot give what it does not first possess, such that whatever exists in an effect must, in some form or other, exist in the cause. From this it follows that non-living substances cannot, qua non-living substances, cause or give rise to living substances. Life is an irreducible category in the material universe.
2) Both living substances and non-living substances are subject to transeunt or extrinsic causation, that is, to causal processes which are effected upon them from without. But what belongs strictly to living substances is the exercise of intrinsic or immanent causation, that is, causal processes such as growth and nutrition, which take place within the organism, and always tend to the integral benefit of the organism. By contrast, the non-living realm is comprised of substances or processes entirely devoid of immanent causation — be it formally, virtually, or eminently. Hence, whatever is entirely devoid of immanent causation cannot bring about substances characterized by immanent causation, since a cause cannot give what it does not first possess. This is why non-life cannot, of itself, produce life. On the A-T analysis, it is not that life arising from non-life is ‘highly improbable’ or ‘unlikely’; rather, it is philosophically impossible.
3) To understand what life is, we must look to those features and behaviors characteristic to all living things. In other words, to explain the essence of any living thing — whether a unicellular or multicellular organic substance, or a unicellular or multicellular organic part of a substance — we must appeal to those features that are common to them all: reproduction, growth, locomotion, and so on.
4) That an organism is alive is determined by the exercise of its immanent powers, such as nutrition, growth, and so on. Whatever the means by which these powers are exercised is secondary to the fact that the organism exercises them. The further question of how nutrition is supposed to be carried out in this organism, growth in that organism, and so on, is a matter of empirical exploration.
5) Is reproductive capacity restricted to organisms? In other words, what is the difference between organic reproduction and the splitting of an inorganic, macroscopic object; or a nucleus undergoing radioactive decay and emitting a particle? Consider first that macroscopic objects split or divide only so far as they are being acted upon by outside forces. They do not exhibit the internal processes characteristic of reproduction. Second, radioactive decay is something that happens to the nucleus; the nucleus does not do anything to itself, nor does it implement any process. Moreover, what the nucleus undergoes is a process of decay, decomposition, or destabilization. But reproduction is nothing of this sort. On the contrary, it is a vital process integral to the functioning organism. In short, when an organism reproduces, it acts; inorganic objects are acted upon.
6) What makes a causal process extrinsic or transeunt is that it always terminates in something other than the cause itself.
7) No inorganic substance can grow in the same manner as organic substances. This is because the ‘growth’ of inorganic substances is purely one of accretion through the influence of outside forces. By contrast, the growth undergone by living beings is intrinsic and self-perfective, that is, it tends toward the regulation and enhancement of the proper functioning of the organism by means of ingestion, assimilation, physical exertion, and so on.
8) Locomotion requires the existence of a capacity which gives locomotion its point. This capacity is known as sentience: the sensory ability to distinguish between good and bad stimuli/environments. Locomotion serves as evidence of sentience when predicated of the organism as a whole. Mere reflex in some part or other of an organism otherwise rooted to a spot (i.e. plants) is not enough to render an organism sentient. Neither plants nor fungi possess locomotion, though they do share the powers of reproduction and nutrition.
9) If the A-T analysis of life is correct, then viruses should not be regarded as living things. They do not metabolize; they do not take in nutrition; they do not grow; they do not maintain homeostasis. In other words, they lack the bare minimum to qualify as living organisms: basic vegetative powers. The host organism in which the virus resides serves as the extrinsic cause by which the virus obtains both energy and material for passive movement.
10) A thing cannot give what it does not have. Hence, chaos could not bestow order without presupposing order at some fundamental level; contingency could not give rise to necessity without containing necessity already; and transient causation could not give rise to immanent causation without immanent causation being present in some form or other. In the words of William Harvey, omne vivum ex vivo. Our experience clearly testifies to this fact.