When reductionism is not enough

Allon Klein pointed me to this fascinating opinion piece from 1972 by Philip Anderson, the Nobel prize winning condensed matter physicist.  (Anderson, PW. 1972.  More is Different. Science 177 393-396).

Anderson argues that it is not possible even in physics, much less in biology, to understand the behavior of complex systems simply by building up from the principles learned by studying the behavior of the component parts. In other words, while reductionism is important and powerful, the fact that you can be a successful reductionist does not imply that you can be a successful constructionist: “The ability to reduce everything to simple fundamental laws does not imply the ability to start from those laws and reconstruct the universe”.

Perhaps this anecdote gives a sense of what drove him to write the article:

“a leader in the field of materials science… urged the participants at a meeting dedicated to “fundamental problems in condensed matter physics” to accept that there were few or no such problems, and that nothing was left but extensive* science, which he seemed to equate with device engineering”.

[* “Extensive” science is here used to describe the process of extending fundamental principles (learned by “intensive” scientists) to explain phenomena.  Anderson was essentially being told that condensed matter physics was a mere practical extension of elementary particle physics, and that his job was to tidy up the leftover phenomena by applying principles discovered by someone else.  You can see how this would have annoyed him.]

I don’t know whether Anderson’s point of view has carried the day in physics — perhaps someone who reads this could enlighten me — but the argument certainly has lessons for how we view biology today. The whole article is worth a read; I include snippets below to whet your appetite.

“The essential idea is that in the so-called N –>∞ limit of large systems (on our own, macroscopic scale), it is not only convenient but essential to realize that matter will undergo mathematically sharp, singular “phase transitions” to states in which the microscopic symmetries, and even the microscopic equations of motion, are in a sense violated….. At some point we have to stop talking about decreasing symmetry and start calling it increasing complication. Thus, with increasing complication at each stage, we go up the hierarchy of the sciences. We expect to encounter fascinating and, I believe, very fundamental questions in fitting together less complicated pieces into the more complicated system and understanding the basically new types of behavior that result.”

“[I]t is not true… “that we each should cultivate our own valley and not attempt to build roads over the mountain ranges… between the sciences.”  Rather, we should recognize that such roads, while often the quickest shortcut to another part of our own science, are not visible from the viewpoint of one science alone.”

“The arrogance of the particle physicist may be behind us… but we have yet to recover from that of some molecular biologists, who seem to be determined to try to reduce everything about the human organism to “only” chemistry.”

Seriously recommended.  Happy reading.