Hierarchic Interactions: The Evolutionary Process
Organisms—biology begins with organisms, and indeed a great deal of the history of biology is a trek through progressively finer subdivisions of organisms. When “forefronts” of biology are listed these days, nearly all concern the molecular biology of intracellular (and intraorganelle) physicochemical processes—and quite rightly so. But the ontology of units larger than organisms, while not wholly neglected, is at least as difficult a problem. Organisms are by far the easiest of biological units for us to see, to probe, to conceptualize as “individuals.” But, in the present context, organisms pose a unique problem all their own: they constitute the only class of individuals to be found in both the genealogical and ecological hierarchies. Consider the confusion that permeates even the recent explicitly hierarchical literature: ecology and evolution (as in the quote from Valentine that stands at this chapter’s head) are generally seen as separate areas of inquiry, but the choice of the higher-level individuals to be incorporated into one’s hierarchy very much depends upon one’s point of view. Below the organism level, of course, the distinction between the somatic and germ lines (i.e., in multicellular organisms) once again ensures a clean separation of the elements of the two hierarchies. Hence the conclusion (Eldredge and Salthe 1984) that there must in fact be two independent, yet parallel and interacting, process hierarchies that together combine to yield evolution. Organisms, as members of both hierarchies, threaten to muddy the picture. It is possible, of course, to distinguish between the economic and reproductive functions of organisms, as I have done at length in the preceding chapter. Physiologists, after all, have long been telling their students that reproduction is the one physiological process not essential to the survival of an organism; thus, it is no surprise that it is invariably the first such process to be dispensed with when the organism is stressed. It is easy to distinguish the economic from the reproductive functions of the vast majority of organisms, but in many vertebrates, most especially Homo sapiens, sexuality has clear economic implications, obscuring the distinction between the two hierarchies perhaps even more.