For the strict neodarwinian, the biosphere cannot evolve in the sense that the biota evolves. However, it may be fruitful to explore the consequences of considering the analogues of genotype and phenotype in the biosphere itself, indeed its evolution in a different sense from the usual definition of evolution for transbiological systems (e.g., superficial descriptive social and cultural evolution). Let us be clear that use of the terms "genotype" and "phenotype" for the biosphere in the discussion that follows should not be taken in the technical sense the terms are used for organisms. Here are my six theses on biospheric evolution:
1. The biosphere is a complex adaptive system, adapting to changing external abiotic constraints (solar luminosity, volcanic outgassing rate, production rate, mass/area of continental crust) (see remarks on Gaia by Barlow and
Waldrop 1994, p. 217), but also self-adapting (e.g., creating new biogeo-chemical subcycles, new steady states as a consequence of biotic, atmospheric, and crustal evolution) and self-selecting (destroying and creating environments and ecosystems, e.g., thermophile and oxygen catastrophes of surface ecosystems, which limited and altered the surface environments of thermophiles and anaerobes, respectively).
2. The biosphere is a self-organizing complex whole. The interpenetration of its parts and its whole includes the nonlinear interaction of the parts, its network of positive and negative feedbacks, the continual reshaping/re-articulation of the parts by the whole, the history of the whole recorded in its parts, transients, and steady-states. The biosphere is a complex totality ("it is a whole whose unity, far from being the expressive or 'spiritual' unity of Leibniz's or Hegel's whole, is constituted by a certain type of complexity, the unity of a structured whole containing what can be called levels or instances which are distinct and 'relatively autonomous', and co-exist within this complex structural unity, articulated with one another according to specific determinations . . ." (Althusser 1970; see Schwartzman 1975). As Levins and Lewontin (1985) put it:
The interpenetration of parts and wholes is a consequence of the inter-changeability of subject and object, of cause and effect . . .. Because elements recreate each other by interacting and are recreated by the wholes of which they are parts, change is a characteristic of all systems and all aspects of all systems.
The whole here is the biosphere; the parts include ocean, upper crust, lower atmosphere, surface ecosystems, and fresh water. The failure to recognize the dialectical interaction of the whole and parts leads to the errors of "holism" and reductionism. An example of relevant holism is the assertion that the biosphere itselfis a living organism. Examples ofreductionism include claims that there are no emergent properties ofthe biosphere, that an understanding of either molecular metabolism or physics and chemistry is sufficient to predict global biogeochemistry from first principles.
It is one thing to assert that the biosphere is a self-organizing complex whole; it is another to ascend from the abstract to the concrete, i.e., to work out on the basis ofempirical evidence the complex dynamics ofsuch a whole and the interaction of its parts. This is a research program that is likely to occupy several more generations of scientists.
3. The genotype of the biosphere is its material inheritance, the sum total of all its parts, embodying its history (genetically coded or preserved), boundary conditions, and structure. Let us assume that the biota evolves in the commonly accepted mechanisms of the neodarwinian paradigm, plus en-dosymbiosis and possibly other mechanisms. In contrast, the biosphere evolves in a Lamarckian mode (acquired characteristics are inherited, constituting its genome). The phenotype of the biosphere is at any time its activity, its metabolism, the character of its biogeochemical cycles (fluxes, steady states, temperatures, partial pressures, etc.). The genotype of the biosphere is the cumulative product of its phenotypes since its birth (the origin of life).
4. The history of the phenotypes of the biosphere is recorded in its parts, that is, fossils, geochemistry of sedimentary and metasedimentary rocks (and possibly even by igneous rocks in so far their chemistry and isotopic composition have been affected by subduction of biogenic sediments), as well as in the genome of the biota [i.e., its enzymatic systems for biogeochemical cycling, the historical geochemistry recorded in its phylogeny, its history of endosymbiosis, e.g., hypersea (McMenamin and McMenamin 1994)]. This is an example ofthe history ofthe whole reflected back into and recorded in its parts. It also creates the potentiality of rapid reemergence and speciation following catastrophe (e.g., big impacts). Of course, the phenotypic activity of the biota is a component of the biosphere's phenotype (Vernadsky's "life as a geological force").
5. The Gaian character of biospheric evolution includes the tight coupling of the abiotic and biotic components, its self-regulation. Its Vernadskian character consists of the progressive changes in biospheric history (cooling, increase in productivity ofbiota, invasion ofthe crust, hypersea, the cumulative increase in diversity of ecological niches over time, etc.).
6. The evolution of the biosphere self-selects a pattern of biotic evolution that is quasi-deterministic in its main contours given similar initial conditions and external perturbations (e.g., impact history). Hence, in the future, with the exploration of space, the theory of comparative biospheres. This view is very Vernadskian: "The non-accidental character of structure and function of the biosphere is a constant theme in Vernadsky's work. . . . The ideas of stochastic variation, undirectedness, and unpredictability were alien views" (Ghilarov 1995).
A heuristic approach to developing a theory of the biosphere was described by Yates (1987b):
At its largest scale, that of the terrestrial biosphere, biological processes will yield to statistical thermodynamic modeling of the overall biosphere-lithosphere-hydrosphere-atmosphere ecological system in which each component shapes the others and is in turn shaped by them [geophysiology]. The global, structural stability of the whole system will again be seen to express six main processes: activation or inhibita-tion, cooperation or competition, chemical complementarities and broken symmetries—all features that can be broadly formulated mathematically. The specifics are, as always, the hard part and progress will be, for along time to come, case-by-case (p. 639).
These concepts of stability are taken from physics and chemistry (e.g., enzymatic inhibition, the broken symmetry of phase transition, self-organization of far from equilibrium systems).
Kauffman (1995) suggested that, as characteristics of their self-organization, local ecosystems evolve to the subcritical-supracritical boundary, whereas the biosphere as a whole is supracritical, evolving inexorably to greater molecular diversity and complexity. In general, supracriticality refers to the state of everexpanding complexity, the self-organization of new ordered systems, whereas subcriticality refers to a state of relatively stable subsystem diversity (e.g., molecular and genomic). However, on a geologic time scale the biosphere, ignoring the possibility of global anthropogenic engineering that may postpone its demise, has a finite lifetime constrained by the sun's inexorable increase of luminosity (see earlier discussion). Thus, future evolution will return the biosphere to the subcritical regime, the "garden of thermophiles," before its extinction, assuming that Kauffman's description is correct.
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