Universal Darwinism and the alleged reduction of biology to chemistry

genesgreenbook.com

by Massimo Pigliucci

A number of weeks ago cosmologist Sean Carroll posted a link on his Google+ stream to a recent paper published by Addy Pross in the Journal of Systems Chemistry. Since Sean’s comment about the paper was positive, I went and checked it out. Essentially, Pross argues that he has come up with a general theory of evolution that bridges biology and chemistry by reducing the former to the latter. The key conceptual element in the new theory is something called Dynamic Kinetic Stability (DKS), to which I will return in a minute. Sean briefly noted that he is generally sympathetic to attempts at extending the Darwinian framework to non-biological domains, as for instance Lee Smolin has done in physics with his idea of cosmological natural selection.

As a biologist I’m much less intrigued by, and indeed tend to be somewhat guarded against, this sort of thing. Moreover, as a philosopher I simply don’t buy Dan Dennett’s idea that “Darwinism” (which of course is not a scientific theory, but an ideological-philosophical position) is a “universal acid,” as expressed most famously in his eminently readable Darwin’s Dangerous Idea.

Perhaps the trouble started with Theodozius Dobzhansky, one of the fathers of modern evolutionary theory, who famously said that nothing makes sense in biology except in the light of evolution (the phrase is, in fact, approvingly quoted by Pross). Problem is, Dobzhansky was writing for an audience of science high school teachers, and his statement is patently wrong, as an even cursory examination of the history of biology makes clear. For instance, developmental biologists had done a lot of highly fruitful research throughout the 19th and 20th centuries even as they ignored Darwin. And molecular biologists made spectacular progress from the 1950’s though the onset of the 21st century, again pretty much completing ignoring evolution. This is not to say that evolutionary theory doesn’t help in understanding developmental and molecular systems, but it is a stretch of the record to make claims such as those of Dobzhansky. (It would be like saying, for instance, that nothing makes sense in physics except in the light of quantum mechanics. Plenty of things in physics make perfect sense even as one brackets quantum mechanics and considers it a background theory.)

Or perhaps the culprit is Richard Dawkins, who famously proposed the idea of memes in his 1976 popular work, The Selfish Gene. Indeed, Dawkins was looking for a way to universalize Darwinian principles, perennially dissatisfied with the emphasis put on contingency by some of his colleagues, most notably the late Stephen Jay Gould. As it turns out, memetics (warmly endorsed as a general theory of cultural evolution by Dennett) failed abysmally, as shown for instance by the premature closure of the Journal of Memetics, the only academic source of all things memetic.

Of course, Darwinian evolution is indeed applicable to some non biological systems, particularly to so-called genetic algorithms, a type of evolving computer program whose properties have been studied by computational scientists over the past few decades. Indeed, genetic algorithms mimic biological evolution so closely that a number of population geneticists I know have been annoyed by repeated claims of computer scientists to have discovered this or that principle describing such systems, apparently without realizing that many of those discoveries had already been made by theoretical population geneticists decades earlier.

But, back to Pross’s paper. His project is not exactly to extend Darwinian principles from biology to chemistry, thus accounting for the pre-biotic evolution of the chemical precursors of living organisms. Rather, he wishes to proceed the other way around and to subsume biological evolution as a particular instance of a chemically-based general theory. This makes sense within the always popular framework of theory reduction, though of course one would then immediately ask why not go all the way and attempt a quantum mechanical model of biological evolution (answer: because such an attempt would quickly begin to look ridiculous on epistemological grounds, if not on ontological ones).

As I mentioned above, Pross’s key idea is that of DKS. As the author puts it: “There is another kind of stability in nature that is actually achieved through change, rather than through lack of change. This stability kind is a dynamic stability,” and proceeds to give the example of a river, which maintains its general feature (stability) even though the actual water making up the river is always different (dynamic). The problem is, of course, that even if biological systems can be thought of as a type of DKS, this is surely not sufficient for an extended theory of evolution, as clearly some not evolving systems — like the above mentioned river — are also DKS.

Pross realizes that his proposal faces serious problems, not the least of which is that while DKS is supposed to be equivalent to fitness, it is exceedingly hard to actually measure DKS. Pross attempts to bypass the issue by asserting that biologists too have trouble measuring fitness, a statement that would surprise many biologists. (There are both conceptual and methodological issues with biological fitness, but nothing like what I gather being the case for DKS in chemistry.)

This is obviously not the place for an in-depth discussion of Pross’s paper (anyone out there interested in a PhD dissertation on various attempts to expand the domain of Darwinian evolution? Drop me a note...). The bottom line is that I am suspicious of theoretical approaches to biological evolution that don’t seem to take on board what the Darwinian theory actually says. As is well known, the best summary of what the latter consists of was given by Richard Lewontin, and it is still today an obligatory station for any serious discussion of “Darwinism.”

Lewontin was able to provide a highly formal and abstract rendition of the Darwinian theory, which boils down to the statement that a given system will evolve in Darwinian fashion if three conditions are met: 1) There is variation within populations of evolving entities; 2) The variants in question differ in their fitness (i.e., their ability to persist and spread); and 3) There is a system of inheritance that allows the next generation to increase the frequency of the successful (higher fitness) variants.

I suspect that Lewontin’s analysis simply doesn’t fit many of the proposed expansions of Darwinian theory. It works for computer algorithms, as I mentioned above, but not for memes (whatever they are), nor — likely — for DKS, and probably not for Smolin’s parallel universes. I guess I’m not bothered by this “failure” because I am happy with scientific theories having proper domains of application and because I’m somewhat suspicious of “theories of everything.” My pluralism about scientific theories is to be taken as epistemologically grounded, not as a deeper ontological statement. That is, I don’t know (nobody does, regardless of what they’ll tell you) whether the total reality of the universe can in principle be described by a single theory unifying all the special sciences. But I think it is pretty plain for everyone but the most dogged reductionist to see that in practice we will have to do with special theories for special purposes, probably forever. Where this leaves the question underlying Pross’s effort — how to bridge the gap between chemical and biological processes, thus explaining what life is — remains to be seen.