Chapter 12
Systems and Networks
Just as we are often interested in events that are composed of many elementary (sim-
ple) events, in biology the objects under scrutiny are vastly complex objects composed
of many individual molecules (the molecule is probably the most appropriate level
of coarse graining for the systems we are dealing with). Since these components are
connected together, they constitute a system. The essence of a system is that it cannot
be usefully decomposed into its constituent parts; it is an integrated whole made up
of interconnected parts. Slightly more formally, following R. L. Ackoff we can assert
that two or more objects (which may be entities, or activities, etc.) constitute a system
if the following four conditions are satisfied:
1. One can talk meaningfully of the behaviour of the whole of which they are the
only parts;
2. The behaviour of each part can affect the behaviour of the whole;
3. The way each part behaves and the way its behaviour affects the whole depends
on the behaviour of at least one other part;
4. No matter how one subgroups the parts, the behaviour of each subgroup will affect
the whole and depends on the behaviour of at least one other subgroup.
There are various corollaries, one of the most important and practical of which
is that a system cannot be investigated by looking at its components individually, or
by varying one parameter at a time, as R. A. Fisher seems to have been the first to
realize. Thus, a modus operandi of the experimental scientist inculcated at an early
age and reinforced by the laboratory investigation of “simple systems” 1 turns out
to be inappropriate and misleading when applied to most phenomena involving the
living world.
1 Here, we plead against the use of the terms “simple system” and “complex system”: the criteria
given above imply that no system is simple, and that every system is complex.
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J. Ramsden, Bioinformatics, Computational Biology,
https://doi.org/10.1007/978-3-030-45607-8_12
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