Biological Mechanisms: Towards a Taxonomy

of Modes of Organization

William Bechtel

The framework of mechanism has proven far more powerful than that of laws for understanding biological systems. Three factors are critical for accounting for the functioning of a mechanism-its decomposition into component parts and operations, the organization of these parts so as to orchestrate their operations, and the embedding of the mechanism in a context which alters and sometimes regulates its functioning. The reductionistic feature of mechanistic explanation emphasizes the decomposition—the determination of what the parts are and the operations they perform. Finding the right parts and discovering productive ways of characterizing what they do are enormous challenges in developing mechanistic explanations. The challenges of discovering how mechanisms are organized and how particular modes of organization foster the orchestration of operations are, however, often even greater. The significance of organization is easily recognized by considering the tasks facing engineers—they begin knowing what component parts and operations are available for designing a mechanism and must figure out how to organize these to achieve a novel outcome. The challenge is sufficiently demanding that success can yield a patent. In the case of biological mechanisms the demands on organization are even greater—biological systems must be able to maintain themselves as organized systems. This entails, minimally, that they be able to recruit energy and selective admit materials from their environment, excrete waste materials back into their environment, and synthesize their own structure from the materials they recruit. I will use Moreno’s term autonomy to characterize the critical feature of biological mechanisms that unlike most human made machines they must maintain themselves.

My focus will be on understanding the ramifications of different modes of organization, especially those that subserve autonomy. Human thinking about mechanisms (even that of scientists) tends to proceed linearly from one operation to the next. Understanding non-linear modes of organization proves extremely challenging. Negative feedback is by now a well understood mode of organization but it had to be repeatedly rediscovered in specific contexts until it was popularized in the cybernetic movement in mid-20^th century. Within biochemistry the concept of cyclic organization is now ubiquitous, but it acquired this status only after many attempts to fit reactions into linear pathways encountered practical limitations such the inability to further oxidize the product of a proposed sequence of reactions (e.g., acetic acid for Thunberg). This resulted in the initially ad hoc proposal that the substance combined with another to produce an intermediate earlier in the pathway. In a step towards a more adequate taxonomy of modes of organization and their implications for the operation of mechanisms, I will focus on two ideas—Tibor Gánti's conception of a chemoton and Albert László Barabási's notion of scale-free networks.