ripheral superiorities. Hominid evolution must also be rethought as reduction of
diversity to a single species of admittedly spectacular (but perhaps quite transient)
current success. In addition, the last 50,000 years or more of human phenotypic
stability becomes a theoretical expectation under punctuated equilibrium, and not
the anomaly so often envisaged (and attributed to the suppression of natural
selection by cultural evolution) both by the lay public and by many professionals
as well.
- Further extensions of punctuated equilibrium include the controversial
phenomenon of "coordinated stasis," or the proposition that entire faunas, and not
merely their component species, tend to remain surprisingly stable in composition
over durations far longer than any model based on independent behavior of species
(even under punctuated equilibrium) would allow, although other researchers
attribute the same results to extended consequences of sudden external pulses and
resulting faunal turnovers, while still others deny the empirics of coordination and
continue to view species as more independent, one from the other, even in the
classical faunas (like the Devonian Hamilton Group) that serve as "types" for
coordinated stasis. - Punctuated equilibrium has inspired several attempts, of varying success
in my limited judgment, to construct mathematical models (or to simulate its
central phenomena in simple computer systems of evolving "artificial life") that
may help us to identify the degree of generality in modes of change that this
particular biological system, at this particular level of speciation, exemplifies and
records. Punctuated equilibrium has also proved its utility in extension by
meaningful analogy (based on common underlying principles of change) to the
generation of punctuational hypotheses at other levels, and for other kinds of
phenomena, where similar gradualistic biases had prevailed and had stymied new
approaches to research. These extensions range from phyletic and ecological
examples below the species level to interesting analogs of both stasis and
punctuation above the species level. Non-trending, the analog of stasis in large
clades, for example, had been previously disregarded—following the same fate as
stasis in species—as a boring manifestation of non-evolution, but has now been
recognized and documented as a real and fascinating phenomenon in itself.
Punctuational analogs have proven their utility for understanding the differential
pace of morphological innovation within large clades, and for resolving a variety
of punctuational phenomena in ecological systems, including such issues of the
immediate moment as rates of change in benthic faunas (previously the province of
hypotheses about glacially slow and steady change in constantly depauperate
environments), and such questions of broadest geological scale as the newly
recognized stepped and punctuational "morphology" (correcting the hypothetical
growth through substantial time of all previous gradualistic accounts) of mutual
biomechanical improvement in competing clades involved in "arms шее," and
generating a pattern known as "escalation." - Punctuational models have also been useful, even innovative in breaking
conceptual logjams, in nonbiological fields ranging from closely cognate studies of
the history of human tools (including extended stasis in the Homo
80 THE STRUCTURE OF EVOLUTIONARY THEORY