916 THE STRUCTURE OF EVOLUTIONARY THEORY
punctuated equilibrium describes the history of most species, the absurdity of the
conventional claim becomes immediately apparent.
The change from Homo erectus to Homo sapiens did not occur in a gradual
and global flux throughout the range of Homo erectus, but as an event of
speciation, geologically rapid under punctuated equilibrium and local in geography
(probably in Africa). By Williams's argument above, the incorporation of the entire
increase into the geological moment of speciation represents no surprise
whatsoever. Why, then, do we misconstrue the rate as maximal over a much longer
anagenetic transformation? We fall into this trap as a simple artifact of the
happenstance that this particular event of speciation occurred very recently—
100,000 to 250,000 years ago by most current estimates. The full transition
probably occurred during the geological moment of speciation, but we erroneously
interpret the change as progressing in gradualist fashion, and at constant rate, from
this time of origin until the present day. Since the moment of origin happened to
occur only a short time ago, the false anagenetic rate becomes very high (for we
integrate the full change over a small interval). But if the identical punctuational
event had occurred, say, 2 million years ago—an entirely plausible, but actually
unrealized, situation— then the same episode of speciation would be read as
anagenetically slow because the identical amount of change would now be falsely
spread over a much longer interval. In other words, the claim for a maximal
anagenetic rate in a trait marking the apotheosis of human success only records a
false interpretation of global anagenesis for the recent cladogenetic origin of this
trait in a punctuational event of speciation.
ECOLOGICAL AND HIGHER-LEVEL EXTENSIONS. The basic logic and
formulation of punctuated equilibrium does not proceed beyond the level of
species treated as independent individuals, or "atoms" of macroevolution. All
biologists recognize, of course, that extensive ecological interactions bind each
"atom" to others in complex ways. The "bare bones" structure of punctuated
equilibrium does not include specific claims about ecological aggregations made of
species as component parts. In this sense, punctuated equilibrium operates as a
"null hypothesis" of sorts, by regarding each species as making its own way
through geological time, with interactions treated as important components within
the set of background conditions needed to explain the particulars of any history.
In this sense, punctuated equilibrium treats time homogeneously, and species as
independent agents; the theory therefore includes no inherent, or logically
enjoined, predictions about the nature of temporal clumping in the ecological
interactions among species.
But we know, as a basic fact and preeminent source of perennial controversy
about the fossil record, that clumping occurs as a major pattern in the history of
life—from minimal (and obvious) expression in joint disappearances during mass
extinctions, to various theories that stress more pervasive and tighter clumping at
several lower levels, all coordinated by the broad notion that ecosystems (or
"communities," or other terminological alternatives, each with different theoretical
implications) operate coherently during normal