Species as Individuals in the Hierarchical Theory of Selection 723
mode. Whatever we invent in one generation, we pass directly to the next by
emulation and instruction.)
The proper species-level analog for ontogenetic drive, or Lamarckian
evolution, sounds a bit bizarre at first—but probably only for the irrelevant
psychological reason that we have so firmly rejected the organismic example,
while promoting the species-level version as a standard mode of change. With
species as individuals and organisms as parts, the gradual transformation (without
branching) of an entire species by organismal selection—the standard, canonical
description of "evolution" itself—becomes the legitimate analog, at the species
level, of heritable ontogenetic alteration, or Lamarckian change, at the organismal
level! If, as tradition used to hold, such ontogenetic drive dominates
macroevolution, then we must record this striking difference in pattern between
levels.
I would argue, however (and under my admittedly partisan commitment to
punctuated equilibrium), that this standard impression is fictional, and that
ontogenetic drive occurs only rarely at the species level. Differences in frequency
will, of course, persist—for mechanisms of inheritance preclude ontogenetic drive
in theory at the organismic level, while the analogous process remains possible in
principle, though rare in fact, given the nature of populations and their modes of
change, at the species level. Thus, small importance remains a common theme at
both levels. Most species originate in a geological moment, and persist in stasis
thereafter (with, at most, mild fluctuation about an unvarying mean, but no
directional change, as the concept of drive requires—see Chapter 9).
I would also venture an analogy to the organismal level in support of inherent
reasonableness for the rarity of anagenesis (ontogenetic drive) at the species level.
As argued above, the Lamarckian mode works with extraordinary rapidity and
efficiency: if organisms changed in this way, we could not fail to notice, because
evolution would then operate so differently. I would suggest that we approach
macroevolution at the species level in the same way. If species changed gradually
most of the time, the pageant of life's history, as shown by the fossil record, would
present an entirely different appearance. The most extensive transformations would
occur in a few million years at most. (Many hypothetical calculations have been
made to illustrate this point—for example, that a small, four-footed, terrestrial
mammal can evolve into the largest whale in a fraction of Tertiary time, so long as
a single population in transformation maintains the smallest effectively measurable
selection coefficient, unabated and without change in direction.)* Stable
*In my favorite more specific example, Williams (1992, p. 129)—who is, to say the
least, no general champion of punctuated equilibrium or detractor of anagenesis—points
out that mean morphological changes in some North American populations of English
sparrows during their century of residence on our side of the Atlantic reach a maximum
of about 5% increase for the lengths of long bones of the wings and legs. This anagenetic
increment, so small that "no birdwatchers will notice in their old age that the bird looks
any different from what they remember from childhood" (Williams, 1992, p. 129), would,
nonetheless, if maintained only for the geologically trivial interval of one million years,
be