920 THE STRUCTURE OF EVOLUTIONARY THEORY
to "glue" component organisms into a higher individual. However, and in response
to my own doubt, the demic level of the genealogical hierarchy manifests a similar
intrinsic leakiness because no strong "glue" exists, in principle, to prevent the
passage of component parts (organisms) from one deme to another. Still, and after
much debate, the efficacy of interdemic selection now seems well established, at
least in certain important evolutionary settings (see pp. 648-652 and Sober and
Wilson, 1998).
Second—and more importantly in raising a theoretical issue at the heart of
evolutionary studies—if the pattern of coordinated stasis and turnover-pulse does
exist with sufficient clarity and frequency, then what forces hold faunas together at
such intensity and for such long intervals, especially in the light of intrinsic
capacity for "leakiness," as mentioned above? (Theoretical debate on this issue has
rightly centered upon the putative causes of coordination in faunal stability, not on
the rapidity of overturn. All formulations agree in ascribing quick transitions
between faunas to direct effects of environmental perturbation.) Roughly speaking,
two proposals of strikingly different import have dominated this debate. Some
authors—in what we may call the "conservative" view, not for any intrinsic
stodginess, but for envisioning no new or unconventional explanatory principles—
hold that faunal stasis requires no active coordinating force at all, but arises as a
side consequence of the environmentally triggered overturns themselves. (Vrba's
formulation, as noted above, tends to this interpretation.) All active control then
falls to the extrinsic causes of rapid overturn, with the coordination in between
merely recording the predicted behavior, under punctuated equilibrium, of species
acting as independent entities. In other words, we see temporal "packages" of
coordinated stasis because external forces impose coincident endings and
beginnings.
But other authors (see Morris, 1996; Morris et al., 1995) advocate active
causal mechanisms, at the level of interaction among species, for holding the
components of ecosystems together during periods of stasis—a notion generally
called "ecological locking," and envisaging an explicit and intrinsic "glue" to build
and then to hold the coordination of coordinated stasis. Morris, for example, cites
the work of O'Neill et al. (1986) on mathematical theories of ecological
hierarchies, in advancing a "claim that ecosystems in frequently disturbed settings
become hierarchically organized such that the effects of large, low-frequency
disturbances do not propagate through the system and cause disruption" (Ivany,
1996, p. 7). Other proposals for "intrinsic" mechanisms of coordination have
invoked the general concept of "incumbency," and tried to designate theoretical
reasons why established associations of species, even if non-optimal and only
contingently or adventitiously built, may resist displacement by active mechanisms
rooted in the behavior and construction of such aggregations.
These admittedly somewhat fuzzy and operationally ill-defined proposals
address, nonetheless, the core of a vitally important issue within the developing
hierarchical extension of Darwinian theory: how far "up" a hierarchy of