Species as Individuals in the Hierarchical Theory of Selection 617
If a search for ultimate reduction below the Darwinian body set the deeper
motivation for choosing genes as units of selection, what particular rationales did
proponents of this theory offer? Both Williams and Dawkins began by arguing that
the conventional unit of Darwinian theory—bodies of organisms—cannot properly
occupy this role because organisms lack a key feature that genes possess. The
bodies of sexual organisms disaggregate in reproduction, making only half an
appearance (so to speak) in the genetic constitution of offspring. How can
something so ephemeral be a unit of selection? But genes pass faithful copies of
themselves into future generations, and therefore maintain the integrity required of
an agent of natural selection in their definition.
Both Williams and Dawkins advance the same argument in three steps: (1) the
unit of selection must be a replicator; (2) replicators must transmit faithful, or
minimally altered, copies of themselves across generations; (3) sexual organisms
disaggregate across generations and therefore cannot be units of selection, but
genes qualify by faithful replication. Williams developed this argument in his first
book (1966), and continues his verbal defense to this day, despite remarkable
movement, as we shall see, towards the position advocated in this volume. But
Williams still employs the language of gene-selectionism, particularly in the
identification of genes as "units of selection" by virtue of faithful replication (so
different from Hull's pluralistic view that the definition of a unit must include both
replication and interaction): "These complications are best handled by regarding
individual [i.e. organismic] selection, not as a level of selection in addition to that
of the gene, but as the primary mechanism of selection at the genie level. Because
genotypes do not replicate themselves in sexual reproduction (cannot be modeled
by dendrograms), they cannot be units of selection" (Williams, 1992, p. 16).
Dawkins (1978) advances the same argument, with the same designation of
genes as units of selection: "However complex and intricate the organism may be,
however much we may agree that the organism is a unit of function, I still think it
misleading to call it a unit of selection. Genes may interact, even 'blend' in their
effects on embryonic development, as much as you please. But they do not blend
when it comes to being passed on to future generations."
In a later book (1982, p. 91), Dawkins affirms the terminology of genes as
units of selection, by making a strong link to his favorite subject of adaptation:
"The whole purpose of our search for a 'unit of selection' is to discover a suitable
actor to play the leading role in our metaphors of purpose. We look at an
adaptation and want to say, 'It is for the good of...' Our quest... is for the right way
to complete that sentence ... I am suggesting here that, since we must speak of
adaptations as being for the good of something, the correct something is the active,
germ-like (sic, but clearly a misprint for the intended 'germ-line') replicator."
Dawkins's extended defense of genes as the unit of selection invokes a set of
related criteria bearing unmistakable concordance with primal virtues of our
culture, another extrascientific reason for the argument's appeal—namely,
faithfulness, (near) immortality, and ancestral priority. Dawkins enlarges the