Victims of History--A Nonequilibrium Approach to Evolution

Abstract

Wiley, E. O., and D. R. Brooks (Museum of Natural History, University of Kansas, Lawrence, Kansas 66045; Department of Zoology, University of British Columbia, Vancouver, British Columbia V6T 2A9, Canada.) 1982. Victims of history-a nonequilibrium approach to evolution. Syst. Zool., 31:1-24.-Evolution may be described as a nonequilibrium process involving the conversion of information from one form to another and the maintenance of old or forging of new reproductive networks. Species participate in nonequilibrium processes because they have properties of closure and because evolution is a historically irreversible phenomenon. Speciation is a process which consolidates available potential information into two or more stored information systems. Character change and the history of a clade are highly correlated because potential information is constrained by its own evolutionary history. Thus new and potential information may be converted into stored information only to the extent that this new and potential information is compatible with the ancestral information system or can find expression in an alternate ontogenetic pathway. All modes of speciation as well as anagenesis follow the second law of thermodynamics and may be described by a summary equation which charts the changes of entropy states of information and cohesion over time. We suggest that some empirical evidence corroborates our theory and that the research programs involved in further studying nonequilibrium evolution are largely in place now. [Evolution; nonequilibrium evolution; speciation; entropy; second law of thermodynamics; information theory.] In a previous paper (Brooks and Wiley, 1982), we suggested that evolution is best explained as an irreversible nonequilibrium phenomenon, and not, as present theories describe, as an equilibrium or punctuated equilibrium phenomenon. We suggested nonequilibrium thermodynamics, as developed by Ilya Prigogine and his colleagues (Prigogine, 1947, 1961, 1978, 1980; Glansdorff and Prigogine, 1971; for a readable summary see Prigogine et al., 1972 and Prigogine, 1980). We did so by considering three aspects of populations and species: information specifying successful growth and ontogeny, cohesion resulting from mating bonds between parts of species (i.e., individual organisms), and energy flow. Our application of information theory followed the conceptual developments of Gatlin (1972), Wicken (1979), Ho and Saunders (1979) and Saunders and Ho (1981). We concluded that speciation, the evolution of diversity in a clade, is accomplished by individual species acting as open-ended, closed, thermodynamic systems-open-ended in terms of energy and closed (or partly closed) in terms of information and cohesion. We suggested that our theory is sufficient to explain variation within species and how speciation is accomplished. We also suggested that extinction could be described using the same parameters. In this paper, we take the opportunity to more fully discuss our thesis. We shall not dwell on competing theories such as neo-Darwinism (the synthetic theory) or punctuated equilibrium except where these theories conflict with or illuminate our own. We will say that if the evolutionary process is, indeed, a nonequilibrium phenomenon and if species, like individual organisms, are dissipative energy structures far from equilibrium, then the assumptions of equilibrium inhibit these theories from fully explaining the phenomenon. In spite of this, we predict that neo-Darwinism and punctuated equilibrium (at least as an empirical observation) will come to rest comfortably within our theory.