Species as Individuals in the Hierarchical Theory of Selection 703
the shunning of Goldschmidt's macroevolutionary ideas as dangerous to the
Darwinian consensus; and the dismissal of group selection as addlepated nonsense
(see pp. 553-556). Nothing in my intellectual life has made me feel more
uncomfortable.
I take great pleasure in the comeuppance of the smug ridiculers in all three
cases. Plate tectonics have validated continental drift to become a new paradigm
for geology. Goldschmidt's particular genetics win no general plaudits, but his
views on a conceptual break between micro- and macroevolution now enjoy
substantial support. The vindication of group selection has been slower, but now
moves on apace (see Sober and Wilson, 1998)—with a vigorous professional
discussion finally occurring, and with general attention now accorded, both in the
popular press (Lewin, 1996), and in the commentary sections of general
professional journals (Morrell, 1996). Sic semper tyrannis.
THE SPECIES-INDIVIDUAL I propose, as the central proposition of
macroevolution, that species play the same role of fundamental individual that
organisms assume in microevolution. Species represent the basic units in theories
and mechanisms of macroevolutionary change. In this formulation, the origins and
extinctions of species become strictly analogous to the births and deaths of
organisms—and just as natural selection works through differential proliferation
based on schedules of organismal births and deaths, so too does species selection
operate upon the frequencies and timetables of origins and extinctions. The next
section of this chapter—entitled "the grand analogy"— shall complete this
argument by attempting to cash out this comparison in detail, with all the
intriguing differences that arise when disparate individuals at two such different
levels work by the same abstract mechanism.
I will therefore confine this preliminary discussion to the three major
objections that have been raised against the foundational idea that species can act
as important evolutionary individuals. These objections treat, in reverse order, the
three words in the key phrase, "important evolutionary individuals." The first
objection holds that species cannot be construed as proper individuals; the second
admits that species are individuals, but argues that they cannot operate as
interactors (as required for units of selection); while the third allows that species
may be recognized as both individuals and interactors, but insists that they must
remain effectively impotent in both roles.
SPECIES AS INDIVIDUALS. The classic argument of evolutionary gradualism
denies real existence to species because they can only be defined as arbitrarily
delineated segments of a lineage in continual anagenesis. Both Lamarck and
Darwin, despite their maximally different views about proposed evolutionary
mechanisms, strongly supported the nominalistic claim that only organisms exist as
natural units, and that species must therefore represent abstractions, formally
designated only for human convenience. (As many historians have remarked,
Darwin chose an odd title for his revolutionary book—for he focusses upon the
explanation of substantial change by anagenesis, and says little about speciation by
branching of lineages.)