606 THE STRUCTURE OF EVOLUTIONARY THEORY
nature, then all the aforementioned problems cannot be avoided and apply in force.
But suppose, as Eldredge and I have long argued in our theory of punctuated
equilibrium (see Chapter 9), that gradualistic anagenesis occurs only rarely in
nature, and that the great majority of species remain essentially stable throughout
their geological lifetimes. (Our concept of stasis recognizes that species fluctuate
mildly throughout time, to an extent no different from ordinary geographic
variation among demes of a species at any one moment, but we hold that mean
values of phenotypes generally do not change in a cumulative or directional
manner.) Suppose also that species, on geological scales, branch in unresolvable
"moments." (In nearly all-geological circumstances, single bedding planes
amalgamate the events and accumulated results of several thousand years.) If
species tend to originate in thousands to tens of thousands of years—that is, with
glacial slowness by the inappropriate criterion of a human lifetime in potential
observation—and then to persist in stasis for millions of years, their origin
becomes instantaneous in geological time, and species arise as discrete individuals
at this proper macroevolutionary scale. Of course, some fuzziness must attend the
origin of a species, for we acknowledge that macromutational beginnings in leaps
of a single generation rarely, if ever, occur. But when "fuzziness" occupies only a
thousand years in a million—that is one tenth of one percent of later existence in
stasis—then geological indefiniteness surely does not exceed even the relative
duration of the fuzziness (9 months in some 80 years) attending the embryo-logical
beginning of human personhood!
Under punctuated equilibrium, the remaining criterion of discrete death
achieves even clearer definition—for nearly all species disappear by extinction
("living on" only through their progeny of daughter species with new names and
individualities), and not by gradual bodily transformation into something else.
Species deaths, at geological scales, are surely more discrete and "momentary"
than human deaths scaled against the lengths of our lifetimes.
In summary, then, species that originate by branching can be individuated
even under the assumption that gradualistic anagenesis prevails during the history
of most species lifetimes (but only by violating our vernacular conception of
"personhood" or individuality). However, if punctuated equilibrium prevails as an
empirical proposition (see Chapter 9 for defense of this contention), then species
are individuals—in some cases much "better" individuals than conventional bodies
of organisms—by all vernacular criteria. Under punctuated equilibrium, species
originate at points of birth with initial fuzziness confined to an insignificant
(usually unmeasurable) moment properly scaled against later existence in stasis.
They experience even clearer moments of death, for nearly all species terminate by
true extinction and not by transformational passage into a descendant that
vernacular (non-cladistic) usage will wish to recognize with a different name (a
phenomenon called "pseudo-extinction" by paleontologists). And species surely
maintain "sufficient stability" during their geological lifetimes by all criteria
outlined on page 602. They remain discrete by reproductive isolation
(conventionally cited, ever