Downward Causation

What is Life? As a chemist studying the origin of life, I’ve posed the question multiple times in this blog. There’s a temptation to describe the chemicals that make up life – if only we could put them together in an appropriate container in the optimum proportions, we would observe life-like characteristics. Needless to say this experiment doesn’t quite work, at least not in the simple naïve picture I have painted.

What is Living? This might be a more useful question, shifting the focus away from solely concentrating on what molecules are present, to how the molecules are interactively functioning within a system. That last phrase, functioning within a system, significantly complicates the matter. Function is context-dependent. You can only define function within a particular environmental milieu, and this makes homing in on a simple universal definition of life very challenging.

This week I’ve been reading and thinking about Downward Causation. What is Downward Causation? It is easier to think about this by first considering its opposite, bottom-up causation: elementary particles in physics explain molecules in chemistry, which explain molecular and cell biology, which explain living organisms. This approach is known as reductionism. It has served very well in advancing progress in the natural sciences. Downward causation is top-down causation: A ‘higher’ level of organization influences the direction taken by its ‘lower’ level components in a hierarchy. This is emergence, the counterpart to reductionism.

How does such emergence, um… emerge? “By informational selection and control.” At least, that’s the answer provided in the book chapter titled “Living through Downward Causation” by Farnsworth, Ellis, and Jaeger, in From Matter to Life. The authors bring together a number of concepts I have previously mentioned: coarse-graining, robust behavior, digital versus analog in biology. They provide several examples ranging from cybernetic systems to ecology as to how all this works out.

You’ll note, wise reader, that I haven’t explained the phrase “informational selection and control”. That’s because I’m still wrapping my mind around the idea – I don’t have a pithy description to trot out as a clear example. (Writing about it, I hope, will help bring some clarity to my muddled ideas.) For a clear exposition of the issues regarding how to think about information in biology and life’s origin, I recommend “The Algorithmic Origins of Life” by Walker and Davies. As to how such information is controlled, I’m up to my eyeballs in a mash-up of cybernetics-meets-statistical-mechanics, which I still don’t quite fathom. Defining macrostates and counting microstates seems to be important. And somehow a situation emerges whereby top-down and bottom-up causation are simultaneously in play.

Some take-away bullet points I’ve come up with:

·      Systems can be both dynamic and persistent.

·      The environment matters, and must be coupled with the system.

·      Different levels in an organizational hierarchy are partly insulated from each other, but pass information and influence back-and-forth.

·      The functional arrangement of the molecules is important, perhaps more important, than which molecules are particularly involved.

·      Modularity, complexity, and energy transduction are tied together in some crucial way.

That’s all I’ve got for now. Enlightenment Later.