Historical Constraints and the Evolution of Development 1137
For example, in commercial areas of Manhattan, we can be pretty sure that a set of
Corinthian columns will be fronting a bank, a government building or a church—so
the generator constrains the function. In residential areas, we can be confident that a
similar set of columns will mark the domicile of wealthy folks, not the entrance to a
public housing project—so the generator also constrains the location and social
setting.
In short, and emphasizing the evolutionary analogy, two similar buildings made
of identical bricks in the cities of Pithom or Raamses are not constrained to be alike
by the structural properties of their admittedly homologous building blocks. The
bricks represent a lowest level, non-specific, non-constraining homologous generator,
and the similarity between the two buildings is convergent, a result of architectural
decisions about good form for an intended purpose—that is, a product of external
selection based on required function, not of internal channeling imposed by
component parts. But the similar form of a town hall in modern America and a
market hall in ancient Rome, as highlighted by their nearly identical facades of
Corinthian columns, must be attributed, in large part, to the complex, highly specific,
phyletically stable design of these chosen architectural modules, which therefore do
constrain the form and function of the buildings in important ways. We may therefore
ascribe much of the similarity to parallelism, based on the common choice of a
homologous building element that establishes a channel of expectation, and has done
so for millennia (and also includes too much complexity and too little flexibility to be
used in many ways beyond the traditional employment). *
Thus, examples of homologous underlying generators form a continuum from
Pharaonic bricks, which are too simple, general, and multipurpose to constrain a final
result in important ways, to Corinthian columns, which are sufficiently complex,
structurally limited in potential utility, and restricted by a long and stable history of
traditional employment, to channel any building into just a few recognized forms and
functions. When underlying homologous generators operate like Corinthian columns,
they entail interpretations of parallelism, rather than pure convergence, for structural
and functional similarities in resulting adult anatomies. But when homologous
generators operate like Pharaonic bricks, they usually do not strongly constrain
similarities between two independent structures built with their aid, and we would
- Such metaphors from distant professions always pay the price of their utility in
suggestive analogy by their occasional capacity to be confusing in their invocation of
different systems with different causal bases. At this point, an architect who loves the strict
Darwinian model would say: "but why is he calling a Corinthian column an internal
constraint rather than an adaptation? After all, I was commissioned to build a bank so I
chose this element as a good fit with my project. The column is therefore an optimal
adaptation based on my skilled selection." But I then reply, "Yes, for you and your building
in a non-Darwinian system. But if an organism carries the genes for Corinthian columns as a
deeply intrinsic aspect of its developmental system, enmeshed in both upstream and
downstream cascades of regulation as both result and promoter, then the organism is stuck
with this eminently serviceable device, and can only construct itself in certain ways under
the constraints imposed by this inherited, internal element."