ance altered from initial stress upon stochastic alternatives to selection to an
auxiliary role for drift (as an impetus for the exploration of new, and potentially
higher, adaptive peaks) as one aspect of a more inclusive and basically
adaptationist process. The complex reasons for this hardening include some
empirical documentations of selection, but also involve a set of basically social and
institutional factors not based on increasing factual adequacy.
- If this hardening on the second Darwinian branch of selection's efficacy
reflects a general trend within evolutionary theory, then we should find a similar
Darwinian strengthening (and narrowing) on the other two branches of selection's
agency (organismal vs. higher levels) and scope (adequacy to explain the entire
geological record by extrapolated microevolution). The triumph (for good reasons
at the time) of Williams over Wynne-Edwards affirms this trend for agency,
although Williams's important clarification then unfortunately hardened (among
epigones) into a dogmatic and a priori rejection of any hint of group selection.
Similarly, the Synthesis's increasing confidence in the exclusivity of gradualistic
microevolution deprived paleontology of any independent theoretical space, and
relegated the field to documentation of an admittedly underdetermined pageant,
built by the exclusive agency of microevolutionary principles. Several synthesists
even denied the efficacy of differential speciation as an input to macroevolutionary
pattern (branding the speciosity of some clades as a "luxury" rather than a crucial
input to survival and flourishing), and attributed all higher-level change to
extensions of gradualistic and adaptive anagenesis within unbranched lineages. - The trends to development, initial pluralism and later hardening of the
Modern Synthesis win clearest expression in two sources of data: comparison of
statements by leading scientists at the two contrasting centennial celebrations of
1909 and 1959 (for Darwin's birth and for the publication of the Origin); and by
documentation of hardening in the summary statements (and increasingly dogmatic
dismissal of alternatives) in leading textbooks for secondary and undergraduate
courses in biology.
Chapter 8: Species as individuals in the hierarchical theory of selection- Selectionist mechanics, in the most abstract and general formulation, work
by interaction of individuals and environments (broadly construed to include all
biotic and abiotic elements), such that some individuals secure differential
reproductive success as a consequence of higher fitness conferred by some of their
distinctive features, leading to differential plurifaction of individuals with these
features (relative to other individuals with contrasting features), thus gradually
transforming the population in adaptive ways. But the logic of this statement
implies that organisms cannot be the only biological entities that manifest the
requisite properties of Darwinian individuality—properties that include both
vernacular criteria (definite birth and death points, sufficient stability during a
lifetime, to distinguish true entities from unboundable segments of continua), and
more specifically Darwinian criteria (production of daughters, and inheritance of
parental traits by daughters). In
72 THE STRUCTURE OF EVOLUTIONARY THEORY