722 THE STRUCTURE OF EVOLUTIONARY THEORY
perspective, but a blessing in richness rather than a nuisance in confusion—drives
at one level can result from selection at a lower level. In the obvious case,
anagenesis within a species—a drive at the species level—traditionally arises from
selection among organisms within the species.)
SORTING (SELECTION AND DRIFT). This descriptive term generalizes our usual
notion of evolutionary change in a collectivity by differential proliferation of some
kinds of individuals vs. others. Sorting, as previously defined (p. 659), is a causally
neutral and purely descriptive term for any evolution by differential proliferation,
whatever the mechanism involved (see original formulation in Vrba and Gould,
1986). Of the two major modes of sorting, selection, based on causal interaction of
traits with environments, ranks as the canonical style of evolution, the essence of
Darwin's insight, and the foundation of modern theorizing. But sorting can also
proceed randomly, a process termed drift. In the hierarchical model, both selection
and drift can occur at all levels, under appropriate conditions. I discussed
previously, for example, how selectively-based sorting of species can occur either
by upward causation from selection at the organismic level ("the effect hypothesis"
of Vrba, 1980, also called "effect macroevolution"), or by selection based on
irreducible fitness of species-level traits in their interaction with environments
(true species selection)—see pp. 652-670.
Ontogenetic drive: the analogy of Lamarckism and anagenesis
The two categories of drive present some of the most consequential and
counterintuitive pairings in the entire table (at least they stimulated my own
thoughts substantially). In a first category, line IIIA, we must acknowledge as an
instance of "drive" any consistently directional change that occurs during the
ontogeny of an individual, and then passes by inheritance to offspring.
We do not usually include such a process in our standard account of evolution
for an interesting reason based on the history of evolutionary thought and the
nature of Mendelian genetics: We generally focus our causal accounts exclusively
on organisms in the Darwinian tradition; at the organismic level, a drive of this
character would validate the most anathematized and fallacious of alternatives to
Darwinism—namely Lamarckism, with "soft" inheritance of acquired characters
(see Chapter 3 on Weismann's use of hierarchical thinking to counteract
Lamarckism). Thus, ontogenetic drives based on phenotypic changes that are
generated by organic activity and then passed to offspring, probably don't exist at
the organismal level due to the nature of DNA and the mechanics of heredity. The
defeat of Lamarckism—ontogenetic drive in this context—marks one of the great
episodes in the history of evolutionary thought. If evolution did proceed in the
Lamarckian mode, the geological history of life would assume an entirely different
appearance, primarily by enormously accelerated rates of change, and suppleness
of adaptive modification. I doubt, for example, that we would find any stable
higher-level entities like species in a Lamarckian world. (Human cultural change
compares so poorly with Darwinian evolution primarily because our customs and
technologies do evolve in this vastly more rapid and flexible Lamarckian