Species as Individuals in the Hierarchical Theory of Selection 605
than by wholesale transformation, no matter how gradual the tempo of
branching—the individuality of species may be maintained in some technical
sense, though only by violation of our vernacular intuitions. After all (see Fig. 8-2),
so long as branching points (or fuzzy intervals) can be temporally located at all,
then species do have definable intervals of existence, and can be individuated on
this basis, even if their life courses violate our usual notions about sufficient
morphological stability.
Many evolutionary biologists have failed to recognize that the so-called
cladistic revolution in systematics rests largely upon this insistence that species
(and all taxa) be defined as discrete historical individuals by branching (leading to
the rule of strict monophyly)—and not as classes with "essential" properties by
appearance (leading to the acceptance of paraphyletic groups). Many biologists
reject (and regard as nonsense) the cladistic principle that no species name can
survive the branching off of a descendant—and that both branches must receive
new names after such an event, even if the ancestral line remains phenotypically
unchanged. But this counterintuitive rule makes sense within cladistic logic—for
cladists define new entities only as products of branching (the word clade derives
from a Greek term for branch). A transforming species that does not branch cannot
receive a new name even if the final form bears no phenotypic resemblance or
functional similarity to the original ancestor. Thus, if such extensive
transformation occurs in un-branched lineages, a cladist, by failing to designate a
truly different anatomy with a distinctive name, retains the technical individuality
of species at the price of a severe assault against legitimate intuition.
Can we find any solution to this dilemma? Must we either deny that species
can be viewed as individuals, or else accept a logically "pure" definition based on
branching, but strongly in violation of vernacular usage? I suggest that this issue
can be resolved empirically, and need not persist as a definitional or philosophical
conundrum. If gradualism and anagenesis prevail in