Why can’t biology or economics be more like physics?

February 12 was the 200th anniversay of Charles Darwin and Abraham Lincoln. I’m not going to comment on either of the two directly in this post (given the large amount of press devoted to them recently) even though their impact on our lives cannot be overstated.  What I do want to talk about is whether or not biology and economics can be more like physics.  I will do this in two parts, with this post focusing on  biology. By “not like physics”, I mean that there is not a more quantitative and unifying approach to biology.  I think many physicists feel that biologists miss the big picture and that much more could be gleaned if they only started to think like physicists.    This attitude is perfectly represented in biophysicist Bob Austin’s letter to Physics Today a decade ago, which can be found here.  I think this view has evolved recently as more physicists work on biology but I still see it.

Although I am a former physicist,  I’m going to take the side of the biologists.  I’m not saying that biology couldn’t be more quantitative and better understood.  I’m also not saying that ideas from physics couldn’t be useful.  These are all probably true.  What I am saying is that the reason biology is not more like physics isn’t because biologists are misguided (or as Bob Austin puts it “can’t reason their way out of a paper bag”) but because biology is different from physics.

Traditional physics (not counting complex systems, which I will get to later) could be thought of as the study of phenomena that obey well defined laws. It is a discipline where theory and experiment have always been tightly bound.   Unlike biology, the uncertainty in a physics experiment is measurement error.  There is rarely a need for statistics to interpret the data.  Progress in physics is cumulative.  New knowledge augments or refines old knowledge.  Although quantum mechanics and relativity revolutionized twentieth century physics, classical mechanics is still useful and valid in well defined regimes.  To use a Darwinian metaphor: Physics is the way it is because what survives as physics is just the phenomena that is that way.

Biology, on the other hand, selects phenomena based on a different criterion, namely relevance to living things.  It is led and constrained by what it can measure, manipulate, and what is interesting or important biologically.  Other than natural selection there are no laws in biology.   And in a delicious twist of irony, it is that very law that makes biology different from physics because exponentially unlikely events are amplified by evolution. Biology is the study of phenomena that intrinsically embody statistical flukes, accidents, trade offs, and transients.

There are certainly fields of biology that are amenable to physics.  Certainly,  molecular and protein interactions do obey the laws of physics and this is where biophysicists have made much progress.  However, once you get to the level of physiology, where I work, the connection to physical law is minimal.  In this regime biology is more like the study of algorithms and devices rather than physics.  Now it is true that most biologists are more concerned with finding all the pieces that comprise the device rather than trying to put them together to see how it all works, which is what I personally try to do. It is also true that many believe that finding more pieces is all that is necessary.  On this point, I vehemently disagree.  I do believe that mathematical theory is crucial for biology but  although I use many of the quantitative tools that are used in physics, what I do is not theoretical physics.  In particular, I never get the satisfaction of knowing if any of my theories or ideas are correct and I think this is the biggest difference between biology and physics (except perhaps string theory, which may or may not be considered to be physics).

The advantage of being guided by laws is that when a model explains the data, it pretty much is correct, or at least in the right ball park because the laws put severe constraints on the form of the model.  When a model in biology explains the data all it has done is explained the data and there are countless other models that can also explain the data.  It is also not clear what needs to be explained because it is not known what part of the data is signal and what part is noise.  All systems are integrated and there may not be obvious ways to separate them in time or space.  So while there could be some undiscovered laws in biology, they are very hard to detect and even harder to prove.  The study of complex systems has similar problems.  Although physicists have been working on this for several decades it’s hard to point to any paradigm shifting insights.  I would argue that chaos theory and critical phenomena have thus far just provided inspiration.

Thus, theories and models are a dime a dozen in biology and get overturned constantly.  We still have no consensus theories about how the brain works, if eating fat is good or bad for you, what causes autism, why bees are disappearing, why you live as long as you do, what most of the genome does, or the origin of life and that is not for a lack of trying.  I think there will be more quantitative and mathematical progress in biology but it will be slow and incremental with problems being solved one at a time.  There may be some general rules of thumb and even laws about some aspects of biological systems but I doubt there will be something firm like Newton’s laws.  However, there is one trait of physics that could be incorporated more into biology and that is optimism.  Physicists are more upbeat and confident about the prospects of finding quantitative theories in biology and that is what is needed for the long slog ahead.