Pardon the loose way data are presented. Typepad is terrible for that sort of thing. Or at least, that's what I've found.
As I mentioned in a previous post, my lab ran down the 285 articles citing CBT 1997 and WG 1998 through 2009. Those articles were scored as follows: 0 - cites to CBT or WG as mere general historical context (or did not make a connection at all); 1 - the area of contention in the article is the exchange between CBT/WG; 2 - the article uses the controversy to contextualize the paper's problem and/or uses Fisher's or Wright's work directly to support the article's central claims. We used only articles scored as a 1 or a 2.
223 articles were scored either as a 1 or 2. The group then studied the papers to determine whether they engaged one of the following nine issues:
1. Fisher's Fundamental Theory of Natural Selection (FTNS)
2. Wright's adaptive landscape metaphor
3. Wright's shifting balance process/theory
4. Importance of epistasis in evolution
5. Population structure
6. Speciation (on the theories)
7. Evolution of dominance
8. evolution in Panaxia dominula
9. evolution in Cepaea nemoralis
These nine issues are either the focus of the original exchanges between Wright and Fisher, or Wade and Coyne, or both. The table shows which topics were discussed most often.
168 of 223 articles focused on one or more of the adaptive landscape, the shifting balance process (or its phases), the role of epistasis in evolution, and the nature/extent of population structure. And here, really, is where we thought things got interesting. Let's leave out the adaptive landscape for now and just consider the shifting balance process, epistasis, and population structure.
The pie chart below shows that of the 85 articles scored on the shifting balance process, most authors thought that the process at least sometimes occurs in nature. (It's hard to say what "sometimes" means, but that's not something the lab can say anything about.) Obviously, this contradicts CBT's claim that the SBT is evolutionarily unimportant, i.e., that, as they say, no case is explained better by the shifting balance process than by the mass selection. When I wrote about CBT/WG back in 2002, my view was that WG were right: there's plenty of room in the evolutionary domain for Wright, Fisher, and no doubt other evolutionary theories. It looks to us like WG are vindicated on this score. In fact, only a few authors thought the shifting balance process never occurred.
And, actually, I think things get more interesting turning to epistasis and population structure. Of the 71 articles taking up the issue of the role of epistasis in evolution, about half believe that epistasis is important in evolution, followed by close to half who believe that it's sometimes important --see the pie below. Now, CBT worked hard to claim that they understand the importance of epistasis in evolution and, in fact, that Fisher himself included it in his natural selection theory. I think the claim about Fisher is problematic: epistasis is relegated to the environmental component of fitness and is virtually ignored. Certainly, Fisher was not thinking about epistasis along the lines of the way that 51% of the biologists engaged in the CBT-WG disagreement were.
Lastly, consider population structure.
Of the 64 articles taking up this issue, most think population structure is more Wrightian than Fisherian. That is, populations are more likely to be smallish and semi-isolated within the global population than with sufficient gene flow to treat them as large and basically panmictic. It struck me as interesting that, in fact, only a few biologists held to the claim that population structure is more Fisherian.
With all that said, take the results together: the shifting balance process sometimes accounts for evolutionary phenomena, epistasis is mostly evolutionarily important, and populations are structured.
A small point can be drawn from this: Coyne and crew are just wrong. In fact, Wright seems to have had much more influence on evolutionary thought than Fisher, if we think of influence as teaching us the right kinds of lessons. After all, it was Wright who emphasized things like epistasis and population structure. (There are other small points, but let's leave them aside for the moment.)
A larger conclusion: It appears that epistasis and/or structured populations are more evolutionarily significant than the shifting balance process. This, I think, is unsurprising since the shifting balance process requires fairly restrictive parameters to work. But if that's true, then what can be said more generally about how evolution works? Is a strong adaptationist view compatible with epistasis singly or in combination? Or do these properties of biological systems require another somewhat general account of evolution, taking into account a shifting balance of evolutionary causes in a way different from Wright (and obviously Fisher)? Or, more difficult, are biologists in a "hunt and peck" situation, looking for whatever combinations of evolutionary processes apply in concert to any given population? That is, sometimes mass selection, sometimes selection and drift, sometimes selection and migration, and so on?
In the lab's view, we might want to go out on a limb and say that it's time to drop Fisher and Wright in our studies of evolution. That is, it's time to drop big frameworks for thinking about how evolution works and trying to apply such frameworks --theories-- to the evolution of populations. Perhaps a bottom-up approach in terms of discovering evolutionary causes of evolution in populations is a better strategy in evolutionary work. Wright said, in 1988, that himself, Fisher, Haldane, and Kimura each proposed evolutionary theories and that all are correct. I would say, now, that such a view is not strong enough --abandon "theories" of evolution altogether because there just aren't any to be had. Instead, search for the combination of evolutionary causes that underwrites particular evolutionary explanations of particular cases of evolution.
Let me try to be a little bit clearer. Some might say that evolutionary biologists are already doing what my lab is suggesting. But I'm not convinced. I think it's plausible to think that some biologists are pursuing a kind of Wrightian strategy: there are plurality of evolutionary theories that explain the evolutionary domain. (Wade and Goodnight said this in 1998. I said it in 2002. No doubt others have said it as well. But not Coyne, Barton, and Turelli. And not others.) We are not suggesting a plurality of theories. We're suggesting that the evolutionary domain requires a (massive) plurality of particular explanations comprised of combinations of evolutionary causal processes to account for the evolution of life. There is no viable general framework like adaptationism or shifting balance or neutralism, or anything else. In this way, evolutionary biology is like, say, molecular biology. There are only causes/mechanisms, not theories. I just don't think that's what evolutionary biologists are doing. Of course, that's an empirical question.
References:
Coyne, J., Barton, N., and Turelli, M. (1997), "Perspective: A Critique of Sewall Wright's Shifting Balance Theory of Evolution", Evolution 51: 643-671.
Skipper, R. (2002), "The Persistence of the R. A. Fisher-Sewall Wright Controversy", Biology and Philosophy 17: 341-367.
Wade, M. and Goodnight, C. (1998), "Perspective: The Theories of Fisher and Wright in the Context of Metapopulations: When Nature Does Many Small Experiments", Evolution 52: 1537-1548.
Wright, S. (1988), "Surfaces of Selective Value Revisited", American Naturalist 31: 115-123.
