1252 THE STRUCTURE OF EVOLUTIONARY THEORY
In any case, although spandrels must originate as necessary side-consequences
of an architectural decision, and not as forms explicitly chosen to serve a purpose,
they still exist in undeniable abundance, and can therefore be secondarily used in
important and interesting ways by clever architects, artists and patrons of buildings. (I
grew up in New York City, and have always admired the lovely ornamentations on
the spandrel courses of many of our finest art-deco skyscrapers, particularly the
zoological motifs on the Chanin Building just opposite Grand Central Station.) In my
"holotype" of the central dome of San Marco's cathedral in Venice, where the entire
interior space has been covered in glorious mosaics, the four pendentives of the
central dome have been ornamented in a complex way, stunningly well "fit" both for
the space occupied, and for the symbolic meanings portrayed by the mosaic designs.
The four evangelists (including St. Mark, the cathedral's patron and most celebrated
resident interred therein) occupy the widest top sections of the spandrels, under a
motto in Latin doggerel: Sic actus Christi, describuunt quatuor isti—thus did these
four describe the acts of Christ. Beneath the evangelists, in the narrowing triangular
spaces, personifications of Eden's four rivers (see Genesis 2) hold amphoras (Greek
pitchers) over their shoulders, each pouring water onto a single flower wedged into
the narrow and elongated space at the base of each pendentive.
The design—beautiful, complex, and particularly appropriate both to Christian
symbolic representation and to the surrounding space—exudes utility. But no one
would make the mistake of arguing that the spandrels exist to house the evangelists.
The spandrels originated as a nonadaptive side-consequence of a prior architectural
decision. These originally nonadaptive spaces were then coopted (several centuries
later, in this case) as "canvasses" for wonderfully appropriate designs. In biological
terms, the mosaic designs are secondary adaptations, and the spandrels themselves
then become exaptations