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altered and refined.' Similarly, he also concludes, 'Early cellular organization
was necessarily modular and malleable.' (2002, p. 8746).
Only with the sealing off of these composite structures and the maintenance of
their identity through growth and replication - i.e., after a few hundred million
years of extremely rapid evolution - did individual lineages become possible.
And with individual lineages (and the predominance of vertical gene transfer),
the operation of the entirely new, albeit far slower,
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kind of selection that we call
Natural Selection. [As Freeman Dyson puts it, 'one evil day, a cell resembling
a primitive bacterium happened to find itself one jump ahead of its neighbors in
efficiency. That cell separated itself from the community and refused to share.
Its offspring became the first species. With its superior efficiency, it continued
to prosper and to evolve separately'. (2005).] Woese calls this the Darwinian
threshold. Much of the variety we see around us is a product of natural selection,
but most of the enzymatic reactions on which these forms are based depend
on proteins and protein machinery that were already in place with the arrival
of single-cell organisms. Furthermore, many of the molecules and machinery
responsible for more recent innovations have been formed by cutting and pasting
earlier structures. In other words, even with the advent of natural selection,
composition (or, to use a currently more popular term, tinkering) seems to have
continued to play a critical role in the creation of novelty.
Probably the most important of such an innovation was the invention of
development, the process by which higher, multicellular organisms are produced.
Development stands in sharp contrast to evolution in a number of ways, but the
contrast between Simon's model of evolution of complex structures by assembly
or composition and the development of multicellular organisms by differentiation
and morphogenesis is particularly sharp. Nevertheless, Simon claimed that the
end result is the same - that multicellular organisms have the same hierarchical
(or modular) structure as that of systems which had formed by composition. It
is the structure, and not its method of production, he argued, 'that provides the
potential for rapid evolution'. (p. 193)
For many people, hierarchy and self-organization constitute opposing
explanatory schemas, with opposing political valences. Despite Simon's demur-
ral, hierarchical construction is often associated with social hierarchy, while
self-organization is understood as organization from below. In fact, however,
self-assembly by composition is itself a form of self-organization, and the
hierarchy that Simon envisioned is simply the consequence of the iteration
of self-organization over time. Where a difference really does need to be
marked is between the iterative processes of self-organization that occur in
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I have not discussed the rates of evolution here, but one of Simon's most important arguments was that the
time required for the evolution of a complex system by assembly is a minute fraction of that required for
evolution by sequential accumulation of novelty (see, esp., pp. 1188-189).
