1176 THE STRUCTURE OF EVOLUTIONARY THEORY
the meaning of this diversity and the causes that bring it about. To many minds this
problem possesses an irresistible aesthetic appeal. Inasmuch as scientific inquiry is a
form of aesthetic endeavor, biology owes its existence in part to this appeal."
After stating the key issue, Dobzhansky then cites the discontinuities within this
diversity as the crucial phenomenon demanding explanation. But he begins this
second subsection, entitled "discontinuity," by unconsciously showing his Darwinian
commitments in citing organisms as the "prime reality" of biology (whereas, in a
hierarchical reformulation of Darwinian theory, several evolutionary levels feature
other biological individuals just as interesting, and just as well constituted—with
Dobzhansky's beloved species, the quanta of his concern for diversity, as a primary
example of individuality at a higher level). Dobzhansky writes (1951, p. 4):
"Although individuals [i.e., organisms] limited in existence to only a short interval of
time, are the prime reality with which a biologist is confronted, a more intimate
acquaintance with the living world discloses a fact almost as striking as the diversity
itself. This is the discontinuity of the variation among organisms."
Dobzhansky then commits his conceptual error in proposing a purely selectionist
explanation—externalist at an extreme in its appeal to environmental topography as
the sole mapping function for discontinuities in organic diversity—for the crucial fact
of dumpiness in the habitation of morphospace. I discussed this passage extensively
in Chapter 7 (pp. 526-528), and will only present a summary here. Dobzhansky
begins by changing the level of application for Sewall Wright's nonadaptationist
model, originally devised to explain why the varied demes of single species may
reside upon several discontinuous peaks of an adaptive genetic landscape. By
promoting this model to the species level (see Fig. 10-31), and regarding the
inhabitants of each peak as a species instead of a deme (and then reconfiguring the
peaks as adaptive optima in an ecological terrain, rather than sets of workable genetic
combinations among demes, with only the highest peak representing an optimum
position for the species), Dobzhansky converted the theoretical meaning of Wright's
model from an explanation for why so many demes have not obtained a best possible
configuration into a paean for the adaptive optimality of each element in a fauna.
In describing this promoted adaptive landscape, as presented in Figure 10-31,
Dobzhansky commits his panadaptationist fallacy by attempting to render the
inhomogeneous occupation of morphospace as a simple one-to-one "mapping" of
discontinuity upon the external "terrain" that set the selective pressures responsible
for crafting all aspects of organic diversity. *
The enormous diversity of organisms may be envisaged as correlated with the
immense variety of environments and of ecological niches, which exist on
earth. But the variety of ecological niches is not only immense,- I apologize for this second citation of a long quote in an overly ample book—see p.
527; but its uncanny appropriateness in these two different contexts leads me to beg your
indulgence for this redundancy.