Circular Logic

The word autopoiesis was coined by Francisco Varela and Humberto Maturana almost half a century ago. It essentially means “self-making”, a key characteristic associated with life. I’ve been working my way through The Systems View of Life by Fritjof Capra and Pier Luigi Luisi. Autopoiesis is introduced in Chapter 7; the authors summarize it like this: “… the cell’s main function is to maintain its own individuality despite the myriad of chemical transformations taking place in it.” While the basic unit is the cell, this concept can be extended to multicellular organisms as a hierarchy of autopoietic units.

 

Earlier in their book, Capra and Luisi tackle the problem of reductionism – the idea that the whole can be reduced into its parts, and nothing but its parts. Emergentism, in contrast, argues that the whole cannot be reduced as such. One way to acknowledge the usefulness of the former without dissolving the latter is to distinguish structure versus property (sometimes called function). While most chemists utilize the rule-of-thumb that structure leads to function, in reality this causal relationship is not so straightforward. Capra and Luisi aver that reductionism is kosher (and useful) when “it limits itself to structure”. On the other hand, “emergent properties cannot be reduced to the properties of the parts”. It then follows that “life as a property cannot be reduced to the properties of the single chemical components.”

 

The authors provide a diagram to illustrate the “cyclical logic of cellular life”. Above is a quick blurry snapshot I took in less than optimal conditions by holding the book up to my laptop camera. One might claim that such circular or cyclical systems are fundamental to the logic of biology – the “bio-logic”. No need to squint at the figure caption as I’ll provide it momentarily. Note that the larger whole includes both the cell (the “bounded system”) and the environment (yet another system?). The circle indicates that the bounded system is “operationally closed”. Note that energy and materials can still flow into and out of the bounded system. This is unlike closed equilibrium thermodynamics systems students learn about in chemistry class, where energy can flow between the system and environment, but not materials.

 

I’ve reproduced the diagram below using PowerPoint and its accompanying caption.

 

Figure 7.3. The cyclical logic of cellular life. The cell, an autopoietic unit, is an organized, bounded system that determines a network of reactions that produces molecular components that are assembled into the organized system that determines the reaction network that… and so on. The terms “input” and “output” – inobservance of the fact that the ell is an open system – represent respectively the incoming of nutrients and energy from the outside, and the outgoing of waste products. The circularity illustrated in the figure corresponds to the notion of operational closure, giving rise to the broader notion of biological autonomy.

 

A brief tangent: Did I reproduce the diagram and text or did I replicate it? I’d say reproduce if this was a physical copy because I didn’t use the same ink or the same tools. Even digitally, the 1’s and 0’s that make up my picture are quite different from the digital photo I took. But if the book and figure were themselves digital and I made a copy of it (with the same sequence of 1’s and 0’s), would this then be a replication? Hmmm… But back to living systems, I’d say DNA replicates but a cell reproduces.

 

In a living system maintaining itself, you’d expect the rate of input to be equal to the rate of output. Students should recognize that this indicates some sort of balance – we call this steady state. Don’t confuse this with the equilibrium state where the rates of all forward reactions and their corresponding reverse reactions are equal, and the free energy of the system is at a minimum. At steady state, energy and materials continue to flow through the system and the cycle likely has a non-zero change in free energy.

 

If the rate of input is larger than the rate of output, than growth can take place. Conversely, if the rate of output is larger than the rate of input, the organism is shrinking, possibly losing both materials and energy – perhaps death is taking place. That’s one way to think about life and death as a continuum of activity. Some organisms even have a period of stasis where all the rates slow down, a state between life and death that we might call suspended animation.

 

Concluding their chapter, Capra and Luisi show a Venn Diagram with three overlapping circles labeled environment, cognition, autopoietic unit. They call this the trilogy of life and claim that “it does not make sense to consider each of these three domains as independent of one another”. Interestingly, I have a similar Venn Diagram with the labels information, interaction, identity – which might substantially overlap with the respective domains described by the authors. Why do Venn Diagrams typically use overlapping circles, but not other shapes? I don’t know. But there are a lot of circles and cycles we see used to describe the logic of life.