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Different Types of Complexity
McShea identifies a number of methodological problems with many
previous studies of complexity increase, and remarks that ``specifying
an operational metric remains a difficult problem''
[McShea 91] (p.318). In a later paper, he
provides a useful analysis of the concept of complexity, and suggests
that it can be broken down into a number of independent measures
[McShea 96]. McShea's hope is that these measures
are both operational (they can unambiguously be measured in real
systems) and universal (they can be applied to all systems).
The definitions that McShea proposes are based upon two dichotomies:
object versus process, and hierarchical versus nonhierarchical
structure. These dichotomies yield four different types of complexity:
(1) Nonhierarchical object complexity; (2) nonhierarchical process
complexity; (3) hierarchical object complexity; and (4) hierarchical
process complexity.^{2.22}
These different types are illustrated in Figure 2.1.
In the context of his work on metazoan complexity, object complexity
refers to morphological complexity, and process complexity to
developmental complexity. McShea discusses various measures and proxies for
obtaining these data from fossils. By taking this narrower, more
specific view of complexity, a much needed degree of objectivity can
be introduced. As a final remark on the notion of overall
complexity, McShea says ``Is a human more complex than a trilobite
overall? The question seems unanswerable in principle because
the types of complexity are conceptually independent ... Thus, it is
hard to imagine how a useful notion of overall complexity could be
devised'' [McShea 96] (p.480).
Figure 2.1:
Different Types of
Complexity. (A, B) Nonhierarchical
complexity: A has greater nonhierarchical object complexity than B (it has more
different parts); B has greater nonhierarchical process complexity than A. (C, D)
Hierarchical complexity: C has a degree of hierarchical object complexity, D has
a degree of hierarchical process complexity. Adapted from
[McShea 96].

Next: Driven and Passive Trends
Up: The Pattern of Life
Previous: Evolutionary Progress
Tim Taylor
19990529