536 THE STRUCTURE OF EVOLUTIONARY THEORY
gene flow, rendered any population ripe for speciation: "The big gaps which we
find between species are preceded by the little gaps which we find between
subspecies and by the still lesser gaps which we find between populations. Of
course, if these populations are distributed as a complete continuum, there are no
gaps. But with the least isolation, the first minor gaps will appear" (1942, p. 159).
But by 1963, Mayr had developed the full apparatus of the distinctive theory
that he later called "peripatric speciation" to emphasize a sharp separation from his
original, continuationist version of allopatry. For the peripatric model promotes the
role of small populations, isolated at the periphery of parental ranges, and subject
to a special maelstrom of influences including greatly enhanced selection and
random effects of the founder principle—all leading to potential achievement of
specific status with relative speed by a "genetic revolution." Mayr says (personal
communication) that he introduced this new apparatus in a paper (1954) that
achieved no impact, but nonetheless represents his most important idea and best
work. (Nihil sub sole novum. He published this paper in a symposium volume—the
greatest repository of unread literature, both then and now.)
- Mayr's 1942 book included little explicit material about adaptation, since
this volume emphasized the origin and development of discontinuity between
species, and said little about anagenetic change within populations. This context of
minimal consideration reflects Mayr's pluralism and lack of commitment to strict
adaptationism at this time. (This claim may sound paradoxical, but should not be
so read. Views expressed in passing—by their simple acknowledgment of an
unchallenged belief—tend to record a professional consensus more clearly than
material explicitly touted as central and distinctive.) But, in 1963, Mayr added a
full consideration of variation and change within populations—the main reason for
a much longer book. Here the hardened, panadaptationist position of the later
Synthesis reigns supreme, perhaps more strongly than in any other book of
comparable influence.
In the mid 1990's, Mayr himself (in lift, and personal communications— see
end of this section), while continuing to explicate and defend his favored themes of
1963, denies any substantial change between the volumes of 1942 and 1963 on
questions of adaptation. This difference between current memory and textual
record, previously discussed as a general principle (see p. 521), provides a
fascinating illustration of how scholars can slowly and unconsciously imbibe a
shifting professional consensus, thus imposing a subjective and personal
impression of stability upon a virtual transmogrification. I find this unconscious
alteration all the more ironic in Mayr's case because his first category of major
change in ideas about speciation—his intellectual move from the dumbbell to the
peripatric model—so strongly encourages a widened space for nonadaptationist
themes (for many evolutionists have interpreted his notions of genetic revolutions
and founder effects in small peripheral isolates as a powerful antidote to the
classical panadaptationist model of Fisherian panmixia in large populations). Yet
Mayr never translated the implications of these changes in his own ideas about
speciation into