NATURAL SELECTION, GAIA, AND INADVERTENT BY-PRODUCTS A Reply to Lenton and Wilkinson’s Response
نویسنده
چکیده
Lenton and Wilkinson (2003), in response to me (Volk, 2002), have offered a number of important ideas for a Gaia theory of ‘regulatory feedbacks’ between life and the global environment. After what are generally positive comments on a selection of their concepts, I focus my reply on one specific point of disagreement. Contrary to the claim of Lenton and Wilkinson, nitrogen fixation is merely another example of how a by-product affects the shared environment among organisms. For Gaia theory to properly incorporate evolution by natural selection, we must distinguish between life’s products and by-products. Because organisms evolve in environments altered by these by-products, I continue to support the idea that feedback loops in the biosphere contain segments based solely upon by-products of organisms’ metabolisms. 1. Agreements with Lenton and Wilkinson To help establish areas of convergence, I first discuss several areas in which I agree with Lenton and Wilkinson’s development of Gaia theory. When I said that Gaia theory ‘involves the search for general principles of the biosphere’ (Volk, 2002), Lenton and Wilkinson have taken it to mean that I require ‘universally true generalities about Gaia’ (Lenton and Wilkinson, 2003, hereafter LW). Let me be clear: I am in accord with LW that we should not expect universal truths, and, furthermore, what matters is to find tendencies in the dynamical organization of the biosphere (I use ‘Gaia’ and ‘biosphere’ as equivalent terms). So we are in agreement over what the search is about. For instance, LW are themselves searching for generalities with regard to what they call ‘regulatory feedbacks’ (more on that later). I think we all agree that the Gaia system is complex, that the Earth’s surface system is more complex with life than it would be without, that the system has dynamics with both positive and negative feedbacks, and that there are a large number of external and internal variables that exert forcings on the system, for example: the sun, extraterrestrial impacts, Earth’s geodynamics, and population fluctuations as well as biological evolution. I also agree that the tendency of the Gaia system to return to a stable state following a perturbation is by itself not particularly interesting, and I am glad that LW concur; such behavior is not one of the general principles that we would trumpet forth as a keystone of Gaia theory. This is because abiotic systems with chemical Climatic Change 58: 13–19, 2003. © 2003 Kluwer Academic Publishers. Printed in the Netherlands.
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