Species as Individuals in the Hierarchical Theory of Selection 637
exclusive units of selection, or causal agents. Bookkeepers must, above all, be
objectivists, not sleuths or storytellers. A good bookkeeper wants an
unimpeachable record, not a causal hypothesis (that can always be wrong). Books
kept in terms of gene frequencies become the best objective records of "descent
with modification" because they do not make causal attributions, but only count
changes ("just the facts, ma'am," to cite a famous detective from the early days of
television). The hierarchical nature of evolutionary mechanics, and the
simultaneous action of selection on individuals at several levels, implies our
inability to know the causal basis of change from records of altered gene
frequencies alone.
Genetic change cannot, of itself, specify the causal level of sorting because
selection at any higher level sorts individuals at all included lower levels as an
automatic effect, and not necessarily for direct causal reasons at all. Two basic
considerations bar inferences of cause from the genetic account books alone. First,
an observation of genetic sorting doesn't specify the relevant causal level. A gene
associated with strong jaws may increase in frequency within the class Polychaeta
because polychaete organisms with strong jaws out compete weaker-jawed
conspecifics in organismic selection; because polychaete species with strong jaws
also develop emergent populational characters that defeat weak-jawed species in
species selection; or because strong-jawed polychaetes do especially well in
driving out jawless priapulids by clade selection.
Second, even when we can identify the level of causality for an incident of
genetic sorting, we cannot know (from the increase in frequency alone) whether
the gene sorted positively has prevailed by a selected effect upon the phenotype, or
for a set of possibly nonadaptive reasons. Does the gene associated with strong
jaws actually promote the construction of this phenotypic basis for organismic
selection, or has this gene hitchhiked to greater frequency by close linkage with
another gene that does build the selected phenotype? Nonadaptive possibilities
only increase for selection at higher levels. If polychaetes have increased by clade
selection over priapulids, does the plurified polychaete gene big-A build part of the
relevant priapulid-beating phenotype, or does big-A just count as one of the myriad
polychaete genes that happen to specify, by homology and a few hundred million
years of evolutionary separation, the historical uniqueness of the clade?
The nature of hierarchies dictates a choice of genes as optimal units of
bookkeeping. The nature of hierarchies also creates a possibility—then realized in
nature for fascinating reasons largely unknown, and mostly beyond the scope of
this book (but see Buss, 1987)—for structuring the world of biology as a hierarchy
of individuals, each encompassing the ones below as new levels accrete in
evolution, and each capable of acting as a unit of selection, a causal agent of
Darwin's expanded theory.
Gambits of reform and retreat by gene selectionists
As I have emphasized throughout this section, gene selectionism can't be made to
work as a general philosophy. The logic of the theory does not cohere, and the
system cannot attain consistent completion. Yet the allure of the