On 2 October 2014, the group met for the third time this semester. This time, we talked about the concept of homeostasis in biology and how the end of homeostasis marks “death.”
Woods, H. Arthur and J Keaton Wilson (2013) “An information hypothesis for the evolution of homeostasis.” Trends in Ecology and Evolution 28(5): 283-289.
Cooper, Steven J. (2008) “From Claude Bernard to Walter Cannon. Emergence of the concept of homeostasis.” Appetite 51: 419-427.
WOODS and WILSON (2013)
Homeostasis: maintaining stability of internal conditions while external conditions fluctuate, especially used of cells and organisms. The concept dates to the physiologist, Claude Bernard as milieu intérieur in his Introduction to the Study of Experimental Medicine, 1865. The term dates to Walter Bradford Cannon, in “Organization of physiological homeostasis”, 1932. Both are closely associated with negative feedback.
Cannon identified 5 key conditions in humans: core temperature and blood concentrations of water (“osmolality”), acid (“pH”), glucose, and calcium.
Homeostasis reflects a series of traits that produce stability. Commonly, they have been considered adaptive because stability protects internal functions from potentially disruptive variations in the environment. Woods and Wilson suggest stability is also adaptive because it minimizes noise in the transmission of biological information.
In discussion, we agreed that this change in focus shifted our viewpoint away from thinking of homeostasis as primary and necessary for life toward thinking of homeostasis as a secondary and continual series of improvements within an evolving system.
Information theory, founded by Claude Shannon, investigates signal processing. Accurate signaling can be improved in four ways: redundancy, distance reduction, clear channels, noise reduction
Woods and Wilson use this as a lens to investigate homeostais. It would explain why even tiny improvements in stability can result in dramatic non-linear improvements in fitness. Conversely, disruptions can result in runaway cascades of failing signals, explaining the relative suddenness of death in higher vertebrates.
“death can be thought of as runaway noise, an emergent set of self-reinforcing dysregulations in multiple homeostatic systems simultaneously.” 286b
We thought that anaphylactic shock provided a good example of runaway noise. Allergen and other triggers can cause the body to release a flood of histamine and other immune signals. The flood causes a number of false signals resulting in a mal-adaptive response to the environment. An epinephrine injection sends opposing signals, reversing many of the symptoms and “resetting” the signaling environment.
The article highlights the concept of homeostasis as a property of the whole body, of which brain function is a vital component. It also highlights the possibility of homeostasis at multiple levels. It also provokes a number of questions:
What is most significant about the individual? (Metabolic and reproductive coordination of cells and organs?)
Within what bounds are conditions regulated? (Skin, fertilization/birth, brain death?)
To what extent do the externalization of systems and regulation relate to death? Consider the placenta and dialysis.
We returned to a common theme in biological concepts of death: context dependent criteria. The biologists felt that their goal was usually utility, rather than rigor. In experimental systems, it’s possible and often easy to set standards that work for the subject in question, even if they don’t apply generally. Thus, neither single instances nor universal categories were important, only operational criteria. One biologist even suggested that one-time instances could not be meaningfully approached with biological epistemology.
Another interesting reflection dealt with our tendency to reason outward from humans to other organisms. Death may seem clearer in humans where we attribute personality and reason to individuals.
Cooper’s article covers the history of homeostasis with an emphasis on the experiments involved and concepts invoked.
Bernard believed that homeostasis required and orchestrator to regulate the body and maintain harmonious function. Only the nervous system could fulfill this function. [Contrast cellular homeostasis.] Along with many contemporaries, he compared the body to the “body politic” reversing the Renaissance (1520) analogy.
‘Paraphrasing Bernard, [JS] Haldane claims, ‘‘Biology must take as its fundamental working hypothesis the assumption that the organic identity of a living organism actively maintains itself in the midst of changing external appearances’’ (Haldane, 1922, p. 391).”’ 423a
The paper also explores historical relationships between homeostasis and negative-feedback (cybernetics) with regard to both signaling and concepts of “organism.”
We spent some time talking about the “body” in English and “corpus” in Latin, when these terms meant the core of a living thing, the remnant of a living thing, and the physical instantiation of a living thing. The history appears complicated and will likely appear in later discussions.
On a religious note: Cannon’s 1932 book The Wisdom of the Body draws it’s title from Job.
“Who has put wisdom in the inward parts,
or given understanding to the mind?” Job 38:36