922 THE STRUCTURE OF EVOLUTIONARY THEORY
conceptual prerequisite for Darwinian theories of causation at the level of
aggregations of species.
PUNCTUATION ALL THE WAY UP AND DOWN? THE
GENERALIZATION AND BROADER UTILITY OF PUNCTUATED
EQUILIBRIUM (IN MORE THAN A METAPHORICAL SENSE) AT
OTHER LEVELS OF EVOLUTION, AND FOR OTHER DISCIPLINES
IN AND OUTSIDE THE NATURAL SCIENCESGeneral models for punctuated equilibrium
If the distinctive style of change described by punctuated equilibrium at the level
of speciation—concentration in discrete periods of extremely short duration
relative to prolonged stasis as the normal and actively maintained state of
systems—can be identified in a meaningful way at other levels (that is, with
sufficient similarity in form to merit the same description, and with enough
common causality to warrant the application in more than a metaphorical manner),
then general mathematical models for change in systems with the same
fundamental properties as species might also be expected to generate a pattern of
punctuated equilibrium under assumptions and conditions broad enough to include
nature's own. In this case, we might learn something important about the general
status and range of application of such a pattern—thus proceeding beyond the
particular constraints and idiosyncrasies of any biological system known to
generate this result at high relative frequency.
Many scholarly sources in the humanities and social sciences, with Thomas
Kuhn's theory of scientific revolutions as the most overt and influential, have
combined with many realities of late 20th century life (from the juggernaut of the
internet's spread to the surprising, almost sudden collapse of communism in the
Soviet Union, largely from within) to raise the general critique of gradualism, and
the comprehensive acceptability of punctuational change, to a high level of
awareness, if not quite to orthodoxy. But the greatest spur to converting this former
heresy into a commonplace, at least within science, has surely arisen from a series
of mathematical approaches, some leading to little utility despite an initial flurry of
interest, but others of apparently enduring worth and broad applicability. These
efforts share a common intent to formalize the pattern of small and continuous
inputs, long resisted or accommodated by minimal alteration, but eventually
engendering rapid breaks, flips, splits or excursions in systems under study: in
other words, a punctuational style of change. These proposals have included Rene
Thorn's catastrophe theory, Ilya Prigogine's bifurcations, several aspects of Benoit
Mandelbrot's fractal geometry, and the chief themes behind a suite of fruitful ideas
united under such notions as chaos theory, non-linear dynamics, and complexity
theory.
Empirical science has also contributed to this developing general movement
by providing models and factual confirmations at several levels of analysis and for
several kinds of systems, with catastrophic mass extinction