by Andre on 3 September 2006
Mohammed AlQuraishi, a graduate student studying genetics at Stanford, just wrote a guest post at Lubos Motl’s Reference Frame “On a Theory of Biology”. He discusses, but doesn’t entirely distinguish, two related ideas: the role of theory in biology and the possibility of a Theory of Biology. I would argue that the first is an important and vibrant field while the second either has existed for a long time or is impossible, depending on your perspective.
Regarding theory in biology, I think it’s important to emphasize that there has already been a variety of significant work: single molecule mechanics, protein folding, membrane biophysics, cell mechanics, cell motility, regulatory networks, and neuronal networks just to name a few! When the topic of theoretical biology is raised it is frequently thought of as something that will happen in the future, once we have that elusive “next generation” of quantitatively trained biologists, but it is happening now and those new to the field (like me) ignore that fact at their own peril.
So what about a Theory of Biology with a capital T? As is often the case in these discussions, physics is held up as a model to be emulated and it’s certainly true that there is a close interplay between theory and experiment in physics, but is it really as unified as is often claimed? I’m not thinking now about quantum gravity, where unification seems like a matter of time (!), but about condensed matter where the situation is more complicated. In one sense, low energy physics, including all of condensed matter, has been unified since Schroedinger, but as Bob Laughlin likes to make painfully clear to his graduate students [pdf], you can’t derive superfluidity from Schroedinger’s equation. Although consistent with quantum mechanics, huge areas of condensed matter, especially soft condensed matter, have essentially nothing to do with it. The situation is similar in biology but even more extreme. Schroedinger’s equation is also, some ideas about homochirality and consciousness notwithstanding, a unified theory of biology, but what is it good for? Well, small scales. But it doesn’t really provide much insight into the larger scale workings even of a bacterium.
Which brings me to my last point. A single meaningful Theory of Biology is not possible. I don’t discount the possibility of more powerful theories of many aspects of biology such as increasingly broad and quantitative “laws of evolution”, or the eventual quantitative understanding of a cell, but a single theory, expressed as a usefully small number of equations or a usefully short algorithm, that accounts for biology from the level of molecules to populations will never be. This isn’t a bad thing, the same way it’s not a bad thing that some equations can’t be solved explicitly. We just need to find other ways that we find satisfying to account for what we observe. Also, this doesn’t mean we won’t have a series of overlapping effective theories that apply at different scales that will ultimately cover the territory from molecules to populations. In fact, I think we’re well on our way down that road.
Instead of a single theory, what we should keep our eyes open for, although not exactly look for—science doesn’t seem to work that way—are new principles that cut across boundaries and can inform theories at every scale like evolution does. Some equally profound principle would be hugely exciting and might still be discoverable, but it won’t be a Theory of Biology.