928 THE STRUCTURE OF EVOLUTIONARY THEORY
a causal and genealogical hierarchy (leg one) can also generate punctuations from
within.
Punctuational change at other levels and scales of evolution
A PRELIMINARY NOTE ON HOMOLOGY AND ANALOGY IN THE
CONCEPTUAL REALM. The simple documentation of punctuational patterns at
scales other than the speciational status of punctuated equilibrium (and, therefore,
presumably attributable to different causes as well) gives us little insight into the
key question of whether or not punctuated equilibrium, in either its observed
phenomenology or its proposed mechanics, can lay claim to meaningful generality
in evolutionary studies. Rather, the overt similarity in pattern must be promoted to
importance through an additional claim, akin in the world of ideas to the weight
that an assertion of homology would carry in assessing the value of taxonomic
characters. What, then, would make an example of punctuational change from
another scale (where the immediate speciational cause of punctuated equilibrium
could not apply) effectively "homologous" to punctuated equilibrium—that is,
sufficiently similar by reason of phenomenological "kinship" that the similar
pattern across disparate scales may be read as revealing the shared components of a
common explanation?
We rank some similarities across scales as capricious enough to be deemed
accidental, and therefore devoid of causal meaning. The appearance of a "face" on
a large mesa on the surface of Mars—an actual case by the way, often invoked by
fringe enthusiasts of extraterrestrial intelligence—bears no such conceptual
homology to faces of animals on earth. We label the similarity in pattern as
accidentally analogous—even though the perceived likeness can teach us
something about innate preferences in our neural wiring for reading all simple
patterns in this configuration (a line below two adjacent circles) as faces. (An
actual face and the accidental set of holes on the mesa top may stimulate the same
pathway in our brain, but the two patterns cannot be deemed causally similar in
their own generation—that is, as faces.)
Identity of specific cause will rarely be available to provide a basis for
asserting meaningful homology, rather than misleading analogy, between common
patterns at disparate scales. Punctuated equilibrium, for example, gains power and
testability in proposing a particular scale-bound reason for an observed
phenomenon—the expression of ordinary speciation in geological time, in this
case. Since most theories win strength by such specificity, conceptual homologies
across scales must seek other definitions and rationales. A punctuational pattern
below the scale of punctuated equilibrium (change within a single deme for
example), or above (temporal clumping in the origin or extinction of many species
within a fauna), could not, in principle, be explained by the specific causes of
punctuated equilibrium itself.
Therefore, meaningful "homology" in this conceptual sense must generally be
sought in properties that are genuinely held in common across systems and scales,
and that operate to channel the different causes of these various scales into the
same recognizable and distinctive pattern. Moreover, such