The Evolutionary Hierarchies

Real-world hierarchies are usually treated as patently evident manifestations of nature, a fact that has somehow rendered them trivial. Familiarity breeds contempt. Everyone knows that atoms are the building blocks of molecules, small molecules combine to form the huge molecules of living Systems, organelles and other structures composed of such molecules make up cells, cells link up to form tissues, tissues do likewise to form organs, thence organ Systems, and finally we arrive at the integrated soma of the organism. And organisms are associated to make populations, or demes, or species. The very names of the subdisciplines of biology (especially as conceived fifty years ago) reflect this organisation. Though molecular biology is a recent arrival, physiological genetics, cytology (and cytogenetics), histology, and physiology nicely recognized the components of the somatic or organismic hierarchy. Thus, the somatic hierarchy retains a heuristic value still reflected in general biology texts. The molecules-to-organism hierarchy offers a handy way of organizing biological knowledge, information about living Systems. That nature itself is organized in such a fashion seems to have slipped to secondary significance. It is, though, common to view the sequences of codons that compose functional genes, as well as other organizational features of DNA molecules, as constituting the retention of information. One major biological hierarchy, the genealogical hierarchy, is evidently a hierarchy of information. It is as if the pragmatic, heuristic, epistemological aspects of biological hierarchies, providing us with a handy way of organizing, summarizing, and communicating what we think we know about biological Systems, serve to obscure the significance of hierarchical organization to the very workings of biological nature. All of this does not deny that there is an extensive literature on hierarchies, a multidisciplinary literature that includes a long, if episodic, history within the realm of biology. The analysis I develop here surely does not arise from a vacuum. Yet the current resurgence of hierarchical outlook on evolution reflects more, I think, a return to an alternative way of looking at nature, a way dictated by a pattern of organization of nature that is there for all to see, than it does the thickening of a continuous Intellectual strand that connects us with earlier interests in hierarchy both within biology and without.