The most special of specialities

As a follow up to my post below, here is a comment over at Uncertain Principles:

Being a lowly biologist myself, I will just note that there is a long tradition of physicists making important contributions in biology (Schroedinger, Pauling), but I can't think of any reverse cases -- that is, biologists who made important discoveries in physics. (That doesn't, of course, mean that there aren't any, and I'd love to hear about some.)

As a point of fact, Linus Pauling was originally a physical chemist. If physical chemists are classed with the physicists I think many biochemistry majors will wonder why we had to take two years of physics instead of the one advertised (ie., we took physical chemistry in addition to physics). Nevertheless, the larger point which I want to allude to is that I can't name a biologist who has gone on to become a physicist, though as I noted in a response comment individuals like Francis Crick have made the move from physics to biology. It seems plausible that the problem is that physics is not just a field of study, it is a set of techniques, methods and modes of thought which requires a lot of hard work and mental training, as well as innate aptitude. In contrast, biology, ranging from ecology to biophysics, mathematical genetics to molecular genetics, is more a domain of knowledge contingent upon the nature of the content. An extremely mathematically gifted child who has an interest in biology will pursue that interest using mathematical techniques. R.A. Fisher was exactly such an individual. Though unlike physics biology is not fundamentally mathematical, it can be. On the other hand, biology is fundamentally about the living world and the patterns emergent from it, while physics is about...the physical world...that is, everything? By saying that physics is about everything I mean to imply that cosmology and particle physics are not symmetric categories in the way life and non-life are. Physics is about applying scientific methods, both theoretical and empirical, to the physical world, and the biological world happens to be a subset of the physical world. Physicists who later develop an interest in biology can transfer many of their habits of mind and techniques (eg., diffusion equations that govern heat flow are applicable to population genetical models). In contrast, biologists who develop an interest in physics later in life will have to climb a rather large mountain of technique which their mind might not be plastic enough to accommodate.

But here is a crucial point: just because most physicists do have a non-trivial potential in applying their skills in the biological sciences, that does not mean that they can pass judgement with any level of credibility from a position outside of that system science. There are many details specific to each domain of knowledge which are implicitly assumed, and so there are many technical issues and nuances which must be internalized in the biological sciences. Biologists often respond to physical scientists passing judgement on evolution by threatening to get involved in the study of partical physics and declaring it ludicruous without due diligence. This analogy is false in that I doubt most biologists could make the transition to being a particle physicist, while I do think many physicists could become biologists later in their careers if they so chose. But, a physicist has to immerse himself in the literature and internalize some of the implicit assumptions of biology, and so, become a biologist, to make credible comment. From the outside the implications of particular equations, like Fisher's Fundamental Theorem, are "clear", but from the inside the difficulties and nuances are understood as background variables which remain "hidden" to an outsider. Just because you are intelligent in the details does not mean you are wise about the big picture.

Addendum: I point to Fundamental Theorem of Natural Selection not because I necessarily think it is particularly relevant to evolutionary biology (though Jim Crow thinks it is, so I'm not going to sneeze at it), but, because I have had a recent experience with seemingly educated individual who used it to disprove the possibility of evolution. Here is Fisher's pupil A.W.F. Edwards, and his verbal characterization of the principle:

"The rate of increase in the mean fitness of any organism at any time ascribable to natural selection acting through changes in gene frequencies is exactly equal to its genic variance in fitness at that time"

The implication here is that selection operates upon variation, and so should exhaust that variation! In other words, selection should eliminate the variation which evolution needs to proceed! This was a nice little nugget of a priori logic which a Creationist put forward to me. As it is, there are problems with this. First, there are serious questions whether the theorem applies beyond one locus, so it isn't so "fundamental" within the discipline of evolutionary biology as my antagonist would have one think. Second, mutation should replenish variation, so at some point one assumes that there would be mutation-selection balance. Third, there is a lot of latent variation within a population, studies over the past century show that selection upon quantitative traits can shift the mean over many standard deviations from generation one. These are just a few of the "implicit" background assumptions one makes when one considers that evolution occurs beause of selection upon heritable variation, they are "understood." My Creationist antagonist was clearly ignorant of this, or assumed I would not be aware of this. I doubt that physicists would be this stupid, nevertheless, I believe many of their errors are of this kind.