Biology Reference
In-Depth Information
critics (discussed in Section 3) who claim that mechanisms and mechanistic
science are inadequate to the phenomena of life.
Part of the challenge of developing an adequate account of mechanism stems
from the fact that when thinking about how mechanisms are organized, humans
tend to think in terms of linear pathways: the product of the operation of one
part of a mechanism is passed to another part of a mechanism, which then per-
forms its operation.
3
But natural systems (and increasingly engineered systems)
rely on far more complex, nonlinear modes of organization. Understanding the
significance of nonlinear modes of organization is daunting, as the history of the
development of the concept of negative feedback exemplifies. Many centuries
passed between its first known application by Ktesibios in approximately 270
BCE to ensure a constant flow of water into a water clock, and its recognition as
a principle of organization that enabled controlled behavior by complex systems.
In the subsequent two millennia it had to be repeatedly rediscovered in different
contexts in which control was needed (Mayr, 1970). For example, windmills
need to be pointed to the wind, and a British blacksmith E. Lee developed the
fantail as a feedback system to keep the windmill properly oriented. When fur-
naces were developed, temperature regulation became important and Cornelis
Drebbel designed such a regulator around 1624. A major turning point in the
recognition of negative feedback as a common design principle followed James
Watt's introduction in 1788 of a governor for his steam engine (Fig. 1). This
became the focus of mathematical analysis by James Clerk Maxwell (1868).
The idea of feedback control was further developed and utilized in a variety of
fields in the late nineteenth and early twentieth centuries. For example, it was
employed for automated ship and airplane navigation; Elmer Ambrose Sperry
developed a version of the gyroscope adequate for such functions in 1908 and in
1910 founded the Sperry Gyroscope Company. During World War I he became
involved in the design of devices to guide anti-aircraft fire and continued to
provide guidance to the US military in the interwar period.
Although the system Sperry developed, the T-6 antiaircraft gun director, used
negative feedback in its internal analog computations, it did not use feedback
from the target (Mindell, 1995). In the 1930s, Norbert Wiener and Julian Bigelow
at MIT tried to apply feedback from the target to control anti-aircraft fire. They
soon encountered an obstacle: if the feedback signal was at all noisy and the
system responded too quickly, the feedback caused it to go into uncontrollable
3
This linear focus is highlighted in Machamer, Darden, and Craver's characterization of mechanisms as
providing continuous accounts from start up to termination conditions. This emphasizes the role of mechanisms
in producing things, but at the cost of downplaying the often cyclic nature of their internal operation. This
tendency is exhibited in the biochemists' portrayal of chemical pathways such as fermentation as linear streams
from starting substances (glucose) to products (alcohol). Various reactions such as the reduction of NAD
+
are shown to the side of the main linear pathway, but following these reactions often reveals cyclic relations
which link different reactions in the main pathway (see Bechtel & Richardson, 1993, Chapter 7).
