930 THE STRUCTURE OF EVOLUTIONARY THEORY
conventional evolutionary jargon in this wider context—meaningful similarity of
genesis (homology) from misleading superficiality of appearance (analogy). As a
first rule and guideline, we might look to the same basic precept of probability that
regulates our general procedures in the study of overt similarity among separate
phenomena: co-occurrence of substantial numbers of potentially independent parts
as a sign of meaningful genetic (and conceptual) connection vs. resemblance based
upon single or simple features, however visually striking, as far more likely to be
unconnected, separately built, and perhaps not even meaningfully alike in any
causal or functional sense (the complex and identical topology of arm bones in a
bat's wing and a horse's foreleg as meaningfully homological vs. my face and the
same disposition of holes on the Martian mesa as meaninglessly analogical). Thus,
and in a practical sense, I focus much of the following discussion upon a search for
what I will call "conjoints," or sets of independent features whose joint occurrence
predisposes us to consider meaningful conceptual homology in punctuational
patterns of change produced by different immediate causes at disparate scales of
size and time. (I have used the same form of argument frequently throughout this
book—as in emphasizing the usual conjunction of openness to saltational change,
belief in the importance of internal channeling, and suspicion about adaptationist
explanation in defining the biological worldview of structuralist thinkers—see
Chapters 4 and 5).
When such broad "homologies" of common structural constraint have been
established across several realms of size and time, then we can most fruitfully ask
some second-order questions about systematic, or "allometric," differences (see
Gould and Lloyd, 1999) in the expression of common patterns along continua
ordered by increasing magnitude among scales under consideration. For example,
do internal forces of cohesion among subparts set the primary basis for active
stasis, or does the "fit" of a structure into a balanced and well-buffered
environment, made of numerous interacting entities, prevent change in a system
otherwise fully capable of continuous alteration in the absence of such
externalities? Does the balance between these internalist and externalist
explanations change as we mount through scales of magnitude? Is the change
systematic (and therefore "allometric" in the usual sense), or capricious with
respect to scale itself, having no correlation with magnitude?
The important principle that meaningful similarity may reside in homology of
structural constraint across scales, while particular causes that "push" phenomena
through these constrained channels may vary greatly, has rarely been stated or
exemplified with proper care, and has therefore usually been ignored by
commentators on the role of events at one scale in the interpretation of others.
Most regretfully, a frequent misunderstanding has then led to dismissal of
meaningful commonality in pattern because a critic notes a strong difference in
immediate causes for a pattern at two scales and then rejects, on this erroneous
basis, any notion of an informative or integrative status for the similarity. Or, even
worse, the critic may become intrigued by a cause just elucidated at one scale and
then assume that the significance of