I realized when I posted my last essay that it was way too long for a blog. This is my attempt to reduce it down to a few paragraphs.
Reductionism in biology is the idea that all levels of enquiry, from cells to physiology to ecology, could in theory be explained by molecular biology, and ultimately by particle physics. Physicalism is the idea that there is only one kind of stuff in the universe, matter (or energy—pick your stuff). I find it strange that the majority of biologists and philosophers of science are both physicalists and anti-reductionists. It seems to me that not only does physicalism require a bedrock theory of reductionism, but that reductionism has proven to be the best strategy we have for understanding nature. I suspect that most anti-reductionists are fearful of determinism, and the debunking of free will that it entails, and this is the motivation behind the inconsistency.
One thing I didn’t explain in my first essay was the distinction between theoretical and ontological reductionism. To be fair, most scientists and philosophers are specifically opposed to theoretical reductionism, which is the belief that all higher level scientific theories will one day be explained in terms of particle physics. The classic example of theoretical reductionism is the reduction of Kepler’s laws of planetary motion to Newton’s laws of mechanics. There are fewer opponents to ontological reductionism, which is the belief that the physical world is ultimately made of one basic unit of physical stuff (this is also known as monism).
The view that anti-reductionists posit is called emergence. This is the idea that there are different levels of biological enquiry that require different kinds of explanation. Certain characteristics of the biological world emerge only when matter interacts in large quantities, creating complex systems with fascinating properties all of their own. The whole is more than the sum of its parts. A classic example of an emergent property in physics is color—an elementary particle doesn’t have a color, but a large collection of particles emit a certain spectrum of light and can then be said to have color.
[Stuart Kauffman (Reinventing the Sacred: A New View of Science, Reason, and Religion) is an example of someone who is a physicalist and at the same time rejects both theoretical and ontological reductionism. Not only does he think that certain properties of biology emerge at higher levels of complexity, he thinks those properties represent real fundamental units of reality (what he calls the “furniture of the universe”).]
Emergence and complex systems theory are fascinating to me, and I think they have a lot to contribute in the near future. Ultimately, though, the core of natural science is reductionistic, and I see no reason to doubt that complexity theories will one day be replaced with fundamental physical theories. This prospect is even more likely if it turns out to be true that the principle of natural selection is actually a law of chemistry, as Alexander Rosenberg has suggested (Darwinian Reductionism or How to Stop Worrying and Love Molecular Biology).