964 THE STRUCTURE OF EVOLUTIONARY THEORY
design illustrates an important reason, more "environmental" than structural, for
the existence of stasis in natural systems: the advantages of incumbency. "The
extinction of clay tablets," Kilgour writes (pp. 4-5) "was ensured by the difficulty
of inscribing curvilinear alphabet-like symbols on clay"; while "the need to find
information more rapidly than is possible in a papyrus-roll-form book initiated the
development of the Greco-Roman codex in the second century A.D." Of this
predominant stasis, Kilgour writes (p. 4): "Extremely long periods of stability
characterize the first three shapes of the book; clay tablets and papyrus-roll books
existed for twenty-five hundred years, and the codex for nearly two thousand
years. An Egyptian of the twentieth century B.C. would immediately have
recognized, could he have seen it, a Greek or Roman papyrus-roll book of the time
of Christ; similarly, a Greek or Roman living in the second century A.D. who had
become familiar with the then new handwritten codex would have no trouble
recognizing our machine-printed book of the twentieth century."
Secondly, the successive stages do not specify segments of an anagenetic flow
(whatever the punctuational character of each introduction), but rather arise as
discrete forms in particular areas—thus following the pattern of branching
speciation so vital to the validation of punctuated equilibrium, and also meeting the
chief operational criterion for distinguishing punctuated equilibrium from
punctuated anagenesis: the survival of ancestral forms after the origin of new
species. Kilgour notes (p. 158) "clay tablets and papyrus-roll books coexisted for
two thousand years, much as two biological species may live together in the same
environment." He also notes, both wryly and a bit ruefully, "that books on paper
and books on electronic screens, will, like clay tablets and papyrus books, coexist
for some time, but for decades rather than centuries" (p. 159).
Third, each form—at least before improved communication of the past two
centuries made such localization virtually inconceivable—originated in a particular
time and place, and in consonance with features of the immediately surrounding
environment, a meaningful analog to the locally adaptive origin of biological
species. Kilgour writes (p. 4): "the Sumerians invented writing toward the end of
the fourth millennium B.C. and from their ubiquitous clay developed the tablet on
which to inscribe it. The Egyptians soon afterward learned of writing from the
Mesopotamians and used the papyrus plant, which existed only in Egypt, to
develop the papyrus roll on which to write."
I know Lester C. Thurow as a colleague from another institution in
Cambridge, MA, but I had never discussed punctuated equilibrium with him, and
was surprised when he used our theory as one of two defining metaphors in his
book, The Future of Capitalism. In distinction to most examples in this chapter,
Thurow does invoke punctuated equilibrium in a frankly metaphorical and
imagistic manner, but he also shows a keen appreciation for the con-joints of
punctuated equilibrium applied to his subject of macroeconomics. Thurow writes
in the context of the collapse of communism in the Soviet Union, and in the
survival of capitalism as a distinctive, effectively universal, and perhaps uniquely
workable system of human economic organization