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Figure 12.11 Adaptation of the environment in telesymbiosis. Hb can tune its loop more closely to that of P by modifying the transfer functions for flow of matter through the environment separating them. Hb can now compete against Ha.

Figure 12.10 A competition between two telesymbioses. Hb competes poorly against HA because its loop is out of tune.

Figure 12.11 Adaptation of the environment in telesymbiosis. Hb can tune its loop more closely to that of P by modifying the transfer functions for flow of matter through the environment separating them. Hb can now compete against Ha.

haps quicker to implement, involves altering the transfer function of the environment separating it from P (Fig. 12.11). If Hb can improve the match by tuning the environment to it, it is now in a position to compete with HA for the carbon put into play by the photoautotroph.

Gaia and the Extended Phenotype

It seems a natural step from the extended pheno-type to the global physiology posited by Gaia. As a rule, evolutionary biologists have been unwilling to take the step, though. This is why I said in Chapter 1 that there would come a point where the evolutionary and physiological perspectives on the extended phenotype might part company. We are now at that point.

The bone of contention seems to be the belief that the evolution of Gaia requires natural selection to operate in a manner that nearly all evolutionary biologists have ruled out of bounds. Group selection is the name given to any kind of selective process that operates at levels above the organism or gene. Classically, group selection has been invoked to explain altruism of some sort: an example would be a gene that prompts certain members of a herd to sacrifice themselves to predators "for the good of the species." Such genes would not last very long, of course, and this is why most Darwinian models for altruism posit genetic subterfuges, like kin selection, that actually promote the interests of the "altruist's" genes. With respect to Gaia and group selection, the point is well made by Richard Dawkins:

... if plants are supposed to make oxygen for the good of the biosphere, imagine a mutant plant which saved itself the cost of oxygen manufacture. Obviously, it would outreproduce its more public-spirited colleagues and genes for public-spiritedness would disappear. It is no use protesting that oxygen manufacture need not have costs: if it did not have costs, the most parsimonious explanation . . . would be the one the scientific world accepts anyway, that oxygen is a by-product of something the plants do for their own good. (Dawkins 1982, p. 236)

I have no disagreement with this statement, except that it is incomplete—it fails to ask why producing oxygen should be good for plants. After all, oxygen holds its electrons very avidly—remember its high oxidation potential—and it takes a lot of energy to strip electrons away from water and force them to take up residence in glucose. Why should the plant work so hard to get electrons when it could get them more easily elsewhere?

The real benefit of oxygen manufacture for plants does not derive from how hard it is to produce oxygen, but from how powerfully oxygen attracts its electrons back. Oxygen's large oxidation potential increases the voltage difference that draws electrons away from glucose, and these "liberated" electrons can be made to do more work. In short, oxygen as an electron donor is sensible only if it can also be an electron acceptor. What confers fitness in this case is that rates of electron donation and acceptance are matched: the genetic identity of the donors or acceptors is of secondary importance. A self-contained loop, such as one which retains oxygen within a plant, may actually generate less power than one which cycles the oxygen to a heterotroph. The plant's fitness could indeed be increased by increasing the fitness of its predators.

Here, then, is the crux of the argument. The evolutionary biologist looks at Gaia and is stopped short by the apparently insurmountable barrier of group selection. The physiologist looks at Gaia and is drawn to it as perfectly reasonable physiology, even if it does require us to define physiology a bit broadly. Who is right, if either? I confess that I am not enough of an evolutionary biologist to say that Gaia is indeed fatally incompatible with current thinking on evolution. But I am a physiologist, and to me, Gaia is where a physiological analysis of the extended phenotype leads.

Animal-built structures come into the picture because these are the agents whereby organisms adap-tively modify flows of matter and energy through the environment. I have offered several examples of this kind of adaptation through this book—the expansion of fractal dimensions of coastlines by coral reefs, the control of energy flow through tidal flats by tube-dwelling worms, the transformation of wind energy by termite mounds, and so forth. In such structures, organisms co-opt the environment into a physiology that extends well beyond their conventionally defined boundaries. And that, in summary, is the point of this book.

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