by Ursula Goodenough

In a recent 13.7 blog , Stuart Kauffman offers a large claim:

"The becoming of the universe and all in it, including the biosphere, and, as we'll see, our economy and culture, cannot be fully described by sufficient natural law."

To be sure, the claim is qualified with fully and sufficient, but several commentators share my uneasy sense that the posting gives an incomplete, and hence perhaps misleading, view of how novelty arises in nature. Since a number of these understandings derive from Stu's own work on complexity theory, their omission may simply reflect blog-imposed word limitations, so consider this post as a complement to his. If it turns out that we disagree on things, then we'll have at it!

Stu cites Murray Gell-Mann's definition of a natural law as "a compact description, available beforehand, of the regularities of a process." He gives Newton's laws as an example, and then asks "Can we have a sufficient natural law for the emergence of swim bladders in evolution? No."

My Webster states that sufficient implies satisfying a need exactly, with nothing wanting and nothing in excess. This is a pretty high bar for any natural law, and indeed scientists regard the fuzzy edge of an understanding as the place where they ply their trade. But I would say that Gell-Mann's definition in fact serves us well in understanding swim-bladder evolution and evolution in general.

When life originated ~ 3.5 billion years ago and then evolved into its myriad forms, it availed itself fully of the laws of physics and chemistry, notably electrodynamics and thermodynamics. Life's core trick is to run chemistry to its advantage and remember how to do it, passing on instructions (genomes) to the next generation. A key feature of the biochemistry is that atoms are constrained into shapes that in turn undergo interactions with one another, generating what are called emergent properties.

Emergent properties are not confined to life -- the surface tension of liquids, the buoyancy of ice, the hardness of a diamond all emerge as a consequence of interactions between the shapes of atoms or molecules. But life has taken this idea to splendid dimensions, with one emergent property (e.g. ion fluxes through membrane channels) serving as the foundation of a more complex emergent property (e.g. transmission of nerve impulses) serving as the foundation of a yet more complex emergent property (e.g. animal behavior). And critically, while ice doesn't remember its buoyancy, organisms reproduce their emergent properties (aka traits) with impressive regularity, again and again, because those that fail to do so fail to pull off the amazing feat of being alive. Traits have functions; they are for something; they have a purpose.

In some hands, emergent properties have been accorded a mysterium -- they are said to be irreducible and unpredictable -- but this is not formally the case. They're irreducible in the sense that they depend on relationship, but not in the sense that they're inherently immune to reductionist analysis, albeit such analyses become increasingly daunting with increasing complexity. They're unpredictable in the sense that they arise only when particular initial and boundary conditions are in place, information that is often not available beforehand. But ice, once it forms, floats on water every time, and genomes, given conducive environmental circumstances, set up internal initial and boundary conditions such that what worked the previous time around happens again.

There are, of course, two variables in the system: the anticipated environment may fail to materialize, and the instructions may change via mutation -- i.e. the Darwinian paradigm. Mutations are usually either lethal or neutral, but when they arise in the context of novel environmental circumstances, they can yield modified protein shapes, and hence modified protein relationships, and hence modified traits that, if better suited to that environment than their forerunners, may spread in a population -- earning them the name adaptations.

A protein with a new shape will usually retain its prior function, performing it in some more adaptive manner, but on occasion it may interact with a new set of proteins and participate in the instantiation of a novel function -- a novel emergent property -- such as switching on a new pattern of jaw-bone development. I've never understand why it's helpful to single out such events as exaptations; they're part-and-parcel of the evolutionary process, indeed one of its natural laws.

Stu also writes of the adjacent possible, a wonderful term that he coined . An apt illustration of the adjacent possible is given by the newly-shaped protein that finds new partners: the partner proteins are fully adjacent -- right there in the same cell -- and their novel interactions are thermodynamically permissible. This is true as well for feathers co-opted for flight: already there, already a promising aerodynamic shape. Same for lung to air bladder: not that big a move. We have sufficient natural laws -- variation and natural selection -- to describe such incremental moves. When the environment changes rapidly and drastically in ways that the cumbersome process of mutation can't address, then the adjacent possible becomes an impossibility, and the result is death or, writ large, extinction.

So if a natural law is a compact description, available beforehand, of the regularities of a process, then I think there's such a description of biological evolution on offer. Biological evolution is based on the generation of instructed emergent properties, operating within the laws of physics and chemistry, that collectively function to constitute a living being; it is driven by mutations that alter protein shapes or regulatory elements and hence either modify existing functions or generate new ones, outcomes that are then subject to natural selection. That we humans are unable to pre-state or predict such events and outcomes in advance may be of philosophical or futuristic interest, but life's been doing just fine without being predictable (as has, for completely different reasons, its quantum underbelly).

Human cultural and economic evolution march to very different drummers than biological evolution -- the adjacent possible, for example, is not necessarily local and proximate, and change operates on very different time scales -- and I look forward to reading Stu's forthcoming blogs on their manifestations within the biological context.

categories: Science and Culture

11:38 - January 2, 2010