630 THE STRUCTURE OF EVOLUTIONARY THEORY
about the question of whether learning, experience, or environmental
influences enter into the development of the behavior. All you have to
concede is that it is possible for a single gene, other things being equal and
lots of other essential genes and environmental factors being present, to
make a body more likely to save somebody from drowning than its allele
would (1976, p. 66).In another passage (1976, p. 39), Dawkins unwittingly surrenders this necessary
tactic by admitting that we dare not discuss the interactive web of embryonic
development, lest we be unable to speak of genes "for" particular aspects of
organismal phenotypes:
Everybody knows that wheat plants grow bigger in the presence of nitrate
than in its absence. But nobody would be so foolish as to claim that, on its
own, nitrate can make a wheat plant. Seed, soil, sun, water, and various
minerals are obviously all necessary as well. But if all these other factors
are held constant, and even if they are allowed to vary within limits,
addition of nitrate will make the wheat plants grow bigger. So it is with
single genes in the development of an embryo. An interlocking web of
relationships controls embryonic development so complex that we had best
not contemplate it.As a striking demonstration that ceteris paribus cannot rescue gene
selectionism from logical paradoxes and violations of ordinary linguistic usage,
Dawkins (1982, p. 164) addresses the problem of how to treat a genetic deletion
favored by natural selection at the organismic level, if genes represent the
fundamental units of selection, and if we must be able to treat each genetic item as
a Darwinian individual with a distinct and independent history. If "gene language"
must prevail, and if we need to specify the selective value of such a deletion, what
can we call the loss but "a replicating absence"! Should we not, at this point, admit
instead that organisms are the relevant causal agents in this case, and that
organisms have achieved a selective benefit by the alternate but orthodox genetic
route of deletion rather than substitution? Some humans have done well with
"plenty of nothing," but I don't think we should root our ontology in taxonomies
for various kinds and forms of faithfully propagating absences.
Any organism that happened to experience a random deletion of part of its
selfish DNA would, by definition, be a mutant organism. The deletion itself
would be a mutation, and it would be favored by natural selection to the
extent that organisms possessing it benefited from it, presumably because
they did not suffer the economic wastage of space, materials, and time that
selfish DNA brings. Mutant organisms would, other things being equal
[ceteris paribus again!], reproduce at a higher rate than the loaded down
"wild type" individuals, and the deletion would consequently become more
common in the gene pool. Here we are recognizing that the deletion itself,
the absence of the selfish DNA, is itself a replicating entity (a replicating
absence!), which can be favored by selection.