PLANT LIFE (PHILOSOPHICAL ASPECTS)

The careful choice of paradigm, or typical cases, enables a broad distinction, at the descriptive level, of inorganic materials, plants, and animals. All three types of natural objects are alike in exhibiting an identifiably stable set of properties, so that it is appropriate, in each case, to speak of a natural mode of action. Beyond this general similarity, however, particular instances of each type exhibit marked dissimilarity.

Descriptive analysis. Plants differ markedly from inorganic systems in their tendency to carry on an active metabolic exchange of materials with the environment. Again, plants grow and mature and even enter resting phases of nearly total inactivity with respect to ordinary organic functions (respiration, metabolism). Plants may reproduce themselves either asexually (by budding or sporulation) or sexually (by pollination), producing one or more new individuals of the same organic type. Tendencies of this sort have no near analogues in inorganic systems. It should be noted, however, that these characteristics are dispositions and not continuously present properties or processes. Even as dispositions, they do not serve as necessary and sufficient conditions for the identification of all living things at the botanical level: sterile botanical forms may very well be referred to as living plants. Again, certain viruses reproduce only when allowed to infect a specific, nonimmune, bacterial host. Thus the question of the vitality of virus-like macromolecules may remain moot while a search is made of appropriate host organisms.

Animals exhibit vegetative activities usually considered philosophically indistinguishable from those found in plants, i.e., they metabolize, grow, pass through an orderly life cycle, and reproduce themselves. The distinction of plants and animals, within the context of the traditional scholastic philosophy of nature, is thought to rest upon the fact that animals possess powers of sensory cognition and appetition, while plants do not. Of course, plants do respond to a wide range of environmental stimuli with activities that are generally adaptive or beneficial to the continued survival of the organism or its species. On the other hand, a line may be drawn between organisms that exhibit definitely formed sense organs and coordinated neuromuscular systems and those that do not (or between those that exhibit plastic behavior patterns that become increasingly adaptive with repeated performance and those whose patterns are absolutely stereotyped or invariable in form). In other words, it seems more appropriate to attribute sensation to those organisms that seem to learn from experience or that spontaneously search out absent sources of food or other stimulation or that exhibit some analogue for affective experience, e.g., "loyalty" to a herd or to a master. One can speak of those higher animals that exhibit such behavior as knowing their environment or having feelings about it without appearing to indulge in metaphor, whereas the use of the terms know and feel with respect to plants is ordinarily regarded as metaphorical.

Evaluation. The descriptive distinctions drawn in the scholastic philosophy of nature between minerals and plants and between plants and animals are reasonable enough and, in fact, are quite compatible with ordinary ways of speaking and talking about these objects. What is contested by nonscholastics is the suitability of this same material as a base for an abstract theory of nature, requiring such explanatory principles as plant and animal souls and nutritive, sensitive, and appetitive faculties.

A number of contemporary points of view contest the distinctions in question as either inconsequential or injurious. The geneticist employs information gathered from the study of bacteria in the elaboration of a general theory of inheritance, hopefully applicable to all living things. The ecologist studies the interaction of all the elements of a given environment; a balanced population involves the commerce of all its organisms without specific regard for their botanical or zoological overtones. For the artist and the man of letters, the picture of nature as an unbroken, continuous chain may be a source of considerable inspiration. The alternative claim that nature is stratified into species and levels that are essentially distinct, while tenable, does not accord so simply with these points of view.

Once it is established that nature is essentially stratified, the traditional distinction between a substance and its powers (e.g., between a living thing and its powers of nutrition, growth, and reproduction) reflects the fact that one can adequately characterize a living thing only in terms of its dispositions or tendencies and that one may insist that a thing is living even when circumstances prevent the activation of these tendencies. It should be noted, however, that scholastic philosophers of science to date have not given biological problems the attention they deserve. With regard to plant life, for example, there is need for clarification of the grounds on which one may urge the view that nature is stratified rather than continuous and for adequate illustration of the point that these grounds can be made intelligible only through a system of substantial forms and powers.

See Also: soul; faculties of the soul.

Bibliography: v. e. smith, ed., The Philosophy of Biology (St. John's Univ. Phil. Ser. 3; Jamaica, N.Y. 1962). a. o. lovejoy, The Great Chain of Being (Cambridge, Mass. 1936).

[a. e. manier]