Darwin's Dangerous Idea - Evolution and the Meaning of Life

218 BIOLOGY IS ENGINEERING
walls in; if you build the vault first, it will spread the walls before the
buttresses can be installed; if you try to build them both at once, it seems
likely that the staging for one would get in the way of the staging for the
other. It is surely a problem that has a solution—probably many different
ones—but thinking them up and then looking for the evidence to confirm or
disconfirm them is a challenging exercise. One strategy that recurs is one we
have already seen in action in Cairns-Smith's clay-crystal hypothesis: there
must have been scaffolding members that have disappeared, that functioned
only during the building process. Such structures often leave clues of their
former presence. Plugged "putlog holes" are the most obvious. Heavy timbers
called "putlogs" were temporarily fixed in the walls to bear the scaffolding
above them.
Many of the decorative elements of Gothic architecture, such as the
elaborate patterns of ribs in the vaults, are really structurally functional
members—but only during the construction phase. They had to be erected
before the "web courses" of the vaults could be filled in between them. They
stiffened the relatively delicate wooden "centering" scaffolding, which would
otherwise have tended to buckle and deform under the temporarily uneven
weight of partially built vaults. There were severe limits on the strength of
scaffolding that could be constructed and held securely in place at great
heights using medieval materials and methods. These limits dictated many of
the "ornamental" details of the finished church. Another way of making the
same point: many readily conceivable finished products were simply
impossible to erect, given the constraints on the building process, and many
of the apparently non-functional features of existing buildings are in fact
enabling design features without which the finished product could not exist.
The invention of cranes (real cranes) and their kin opened up regions of the
space of architectural possibility that were previously inaccessible. 19
The point is simple, but casts a long shadow: When you ask functional
questions about anything—organism or artifact—you must remember that it
has to come into its current or final form by a process that has its own
requirements, and these are exactly as amenable to functional analysis as any
features of the end state. No bell rings to mark the end of building and the
beginning of functioning (cf. Fodor 1987, p. 103). The requirement that an
organism be a going concern at every stage of its life places iron constraints
on its later features.
19. Foui classic explorations of these issues are John Fitchen's The Construction of
Gothic Cathedrals, which reads like a detective story, Fitchen's Building Construction
Before Mechanization ( 1986), William Barclay Parsons' Engineers and Engineering in
the Renaissance ( 1939, republished by MIT Press, 1967) and Bertrand Gille's Engineers
of the Renaissance ( 1966 ).
FIGURE 8.1. Early rotating cranes and other
devices for raising or moving loads. (From Diderot and d'Alembert, Encyclopedic
[1751-1772], reproduced in Fitchen 1986.)