Control Systems in the Living World - Building the Most Complex Structure on Earth - page 18

which implies maintenance of a constant ratio of the components of the system,
despite variations in nutrition, as well as the ability of the system to restore its nor-
mal state after disturbances caused by external agents. Von Bertalanffy called such
states equifinal (from the Latin aequus , “equal,” and finalis ,“pertaining to the end”)
and he invented the term equifinality to refer to the biological phenomenon ( von
Bertalanffy, 1950 ).
In order to sustain their vital functions, living systems need to create steady states
(within certain limits) of their chemical and physical parameters, and they must
maintain that state even under hostile environmental conditions. As shown in the
preceding section, even without the influence of harmful environmental agents, the
unavoidable degradation of structure determined by the thermodynamic forces of
degradation will occur. In addition, the exceptional complexity of cells and multicel-
lular organisms and the high improbability of their structure require an organism's
internal environment be within ranges that allow normal functioning of the cell or
organismic machinery in multicellulars.
The French biologist, philosopher, and author (dramatist) Claude Bernard (1813-
1878) coined the term “ la fixité du milieu intérieur ” to describe the property of liv-
ing systems to maintain a constant internal environment, which he considered to be
“the condition for a free and independent life.” Later, Walter Cannon (1871-1945),
a Harvard physiologist, expanded the concept in his topic The Wisdom of the Body
(1932) and used the term homeostasis (from ancient Greek όμος ( hómos ), “similar,”
and στάσις ( stasis ), “stable”) to describe the relatively constant state of the internal
environment of living organisms ( Cannon, 1963 ).
Homeostasis is loosely defined in different ways, but its classical meaning
describes both the constancy of the internal environment (i.e., of the body fluids
in animals or plants) and the biochemical and physiological processes that deter-
mine the constancy. In this broad meaning, it implies the constancy of the proto-
plasm in prokaryotic and eukaryotic unicellulars, including cells of multicellulars.
Conventionally, in multicellular organisms, homeostasis is used to describe the
chemical constancy of extracellular and body fluids (blood, lymph, etc.), which is
necessary for the normal functioning of all the organism's cells. But each cell must
also maintain a constantly normal internal environment. In line with my epigenetic
theory of heredity and evolution, I use the term homeostasis in an even broader way,
to include the maintenance of the integrity of the structure of both unicellular and
multicellular organisms.
The control system (see the section “Control Systems” later in this chapter) is
tasked with homeostasis. In multicellular animals, the control system closely moni-
tors the homeostatic parameters and, based on various feedback loops, adjusts their
level within the normal range, according to species-specific set points.
Most homeostatic parameters in animals are determined by the brain. The ubiq-
uitous presence of the nervous system in the animal body allows the brain to receive
current data on every part of the organism via afferent nerves. It compares the actual
data with the set points to determine deviations from the norm, and, via efferent
pathways, it sends instructions for restoring the normal levels of homeostatic param-
eters. In a simplified, generalized form, the control system of living systems (from