Species as Individuals in the Hierarchical Theory of Selection 635
Crow explained why our traditions have favored the genetic level of analysis
(1994, p. 616):
The reason, I think, is that these pioneers [Fisher and other founders of the
Synthesis] and their intellectual heirs have been concerned, not with
selection as an end in itself, but with selection as a way of changing gene
frequencies. Selection acts in many ways: it can be stabilizing; it can be
diversifying; it can be directional; it can be between organelles; it can be
between individuals; it can be between groups ... But the bottom line has
always been how much selection changes allele frequencies and through
these, how much it changes phenotypes. This suggests that we should judge
the effectiveness of selection at different levels by its effects on gene
frequencies.
I could not ask for a better statement of (unconscious) support for the position
here maintained. Again, as I noted in several other quotations from gene
selectionists, Crow allows that selection, as a causal force ("selection as an end in
itself," in his words), operates on interactors at several hierarchical levels of
individuality, including groups. He also admits that changes in gene frequencies
arise as a result of such selection. He then states—and again I don't object—that
these alterations in allelic frequencies should be read as a "bottom line" in
judgments about selection's effect. Nicely said, but a bottom line for what? Crow
then gives his crucial answer—for keeping the books of evolutionary change: "we
should judge the effectiveness of selection at different levels by its effects on gene
frequencies." Altered gene frequencies are therefore results (for bookkeeping),
while selection (the cause of the changes) operates upon interactors "at different
levels" of individuality.
This notion of a "bottom line" also provides our best entree into the third and
most important reason for choosing genes as units of bookkeeping: the intrinsically
asymmetrical nature of causal flow in hierarchies of inclusion. I particularly
appreciate the doubly amplified utility of hierarchy theory in this example—for the
hierarchical view, as I shall show, both serves as a replacement for gene
selectionism, but also (in a situation not devoid of irony)* provides the rationale
for why many biologists chose, albeit for fallacious reasons, to focus on genes in
the first place!
We do need to keep the books of evolutionary change, and bookkeeping does
require a basic unit of accounting. Candidates for this status must obey the primary
criterion always stressed by gene selectionists: faithful replication. But genes do
not exhaust the range of faithful replicators. Asexual organisms and species also
rank as sufficiently faithful. Reductionistic preferences in general, and claims for
relatively greater faithfulness of genie vs. higher-level replication, might set a
preference for genes—but another crucial argument, usually unrecognized or
unmentioned, sea ls the case.
*The logic of this case recalls the celebrated example (see pp. 492-502) of
Rutherford's use of radioactivity both to impugn the theoretical basis for Kelvin's young
age for the earth and then to provide the empirical basis for measuring a revised and
much older age.