Reductionism and Darwinian evolution: what do they have to do with each other? A lot, as I will shortly explain.
But first a couple upcoming events. The Institute for the Study of Nature (ISN) has announced its plans for its annual Summer Seminar and Conference, June 15-20, 2009 at MIT. This year's theme is "Reduction, Emergence, and Essence." In other words, it's about the limits of the scientific strategy of explaining wholes by breaking them down into parts, about the rising tide of emergentism, which tries to recover the wholeness of things, and about the need to go back to the classical (philosophical) language of essence in order to return science to the world we actually live in. This year, ISN is offering scholarships to the Seminar and has even made printable publicity materials available to be downloaded from the website. The deadline for applying is fast approaching: check out the website.
But if you're in no way constrained to the Western hemisphere, you may want to check out a prior and unrelated event, the conference on evolution in Rome next month: Biological Evolution: Facts and Theories: A critical appraisal 150 years after "The origin of species", 3-7 March 2009 at the Pontifical Gregorian University.
Of course this year is the 200th anniversary of Darwin's birth, as well as the 150th anniversary of his book On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. The New York Times has a special spread celebrating that work (and, knowing the Times, by implication the license they think it gives them to disregard any moral constraint they find inconvenient).
Darwin's The Origin of Species says much less than people think it does. I have recently been doing some reading on reductionism and, in an insightful paper by Thomas Nagel (NYU professor of philosophy and law), I ran across a paragraph that, without being directly about Darwin's theory, has strong implications for understanding it:
How could the following two propositions both be true?
- Every event that happens in the world has a fundamental physical description and a fundamental physical explanation.
- Some facts about the world do not have a fundamental physical explanation, but do have a higher-level explanation.
The answer is that they could both be true if the higher-level explanations depended on principles governing the relations between general types of phenomena or properties that were not subject to correspondingly general characterization in ultimate physical terms, even though each instance of such a phenomenon had a distinct ultimate physical characterization. Perhaps not all naturally important kinds correspond to kinds definable in basic physics. If that were so, the laws operating at the higher level could not be derived from corresponding laws couched at the fundamental level, even though each event falling under the higher-level laws could be given a separate ultimate explanation. (7)
The most important sentence here is "Perhaps not all naturally important kinds correspond to kinds definable in basic physics." As an illustration of this, take what he says earlier:
Even though new levels of [reductionistic] explanation become available over time, they do not necessarily result in the elimination of the old [less reductionistic explanations]. For example, I gather that explanations of heredity in terms of classical genetics, descended from the Mendelian theory, are not about to be simply replaced by explanations in the language of molecular biology (Kitcher 1984). (5)
(Yes, I've snatched this out of context, but it's still a good example here.)
Of course, Darwin's triumph was to break down the last barrier to Newton's blind, mechanical universe. Darwin extended mechanism to living things. The fundamental problem is that organismic species are not "definable in basic physics." If one looks at the universe exclusively in a mechanical (Darwinian) way, there are no species, but only individuals1 who may or may not have enough genetic heritage in common to allow their interbreeding. But even given that they can interbreed, there's no guarantee that their offspring will be of the same "kind" (i.e., or whether elephants might give birth to the occasional giraffe, so to speak). Indeed by Darwin's lights, there are no "kinds."
So the great irony is that the consequence of Darwin's The Origin of Species is that there are no species, but only a vast continuum of various individuals.2
Of course, this is only a problem if one takes Darwin to be a complete worldview. Nonsense, such as the claiming the non-existence of species, makes it very clear that, while the Darwinian theory has real virtues and provides insights into the origin of life-forms, it is not a complete worldview.
What's really real in reductionistic theories are the particles3 of which things are composed; everything else is just a modification of the particles' configuration and motion. Darwin's theory suffers from the same weakness as all reductionistic theories: it cannot account for the reality, the meaningfulness, of the high-level concepts that we use in our everyday lives.
1. Actually if we want to take the reductionistic point of view seriously, there aren't even individuals, but only temporary clouds of matter that for convenience we call individuals.
2. Of course, there are always two sides to an issue. The Times highlights the selection from the Origin in which Darwin claims that "species come to be tolerably well-defined objects," since individuals representing intermediate forms would be rare. But rare is not impossible (hence the hedge "tolerably"). Darwin's philosophically consistent 20th-century interpreter Ernst Mayr saw the weakness of this claim. Of course, expecting philosophical rigor from Darwin (or the Times) is as realistic as expecting doctrinal rigor from Anglicans (no coincidence: Darwin was trained as an Anglican clergyman).
3. One wonders why we need to stop reduction at these particles.
Thomas Nagel 1998 "Reductionism and antireductionism," The limits of reductionism in biology. Wiley, Chichester (Novartis Foundation Symposium 213), 3-14.