Development: Three Grades of Ontogenetic Involvement 193phenotypic plasticity is the immediate adaptive adjustment of pheno-
type to the production of a novel trait or trait combination...Phenotypic
accommodation reduces the amount of functional disruption occasioned
by developmental novelty.” [West-Eberhard, 2003, 147]“Adaptive phenotypic adjustment to potentially disruptive effects of
the novel input exaggerate and accommodate the phenotypic change
without genetic change.” [West-Eberhard, 2005a, 613].The accommodation of one part of an organism’s phenotype often requires, and
elicits, accommodation by others. In the process it occasionally produces novel,
stable, adaptively advantageous phenotypes. The generation, by development, of
novel adaptive phenotypes has further consequences.
Developmental recombination: “Developmental recombination occurs
in a population of individuals because of a new, or recurrent input. A
new input... causes a reorganization of the phenotype, or “develop-
mental recombination”. Given the variable developmental plasticity of
different individuals, this process produces a population of novel vari-
able phenotypes, providing material for selection”. [West-Eberhard,
2005b, 6544].For any novel phenotype, there may be within the population many alterna-
tive developmental systems capable of producing it; some combinations of them
will be better than others at reliably producing the new phenotype. Repeated
developmental recombination will have the effect of lowering the threshold for the
development of an adaptively advantageous novelty (Cf[Waddington, 1957]).
Genetic accommodation: “If the phenotypic variation is associated
with variation in reproductive success, natural selection results; and
to the degree that the variants acted upon by selection are genetically
variable, selection will produce genetic accommodation... ” [West-
Eberhard, 2005a, 612]. Genetic accommodation is “...adaptive evo-
lution that involves gene-frequency change”. [West-Eberhard, 2005b,
6544].On this model, adaptive plasticity, a feature of development, is both the cause
of the adaptedness of organisms and the diversity of organic form.
This is a radical proposal. It reverses the causal priority of genotype over phe-
notype in evolution that is the cornerstone of sub-organismal, replicator interpre-
tation of the modern synthesis. Phenotypic novelties are initiated in development
and not by mutation. Palmer [2004] calls this a “phenotype before genotype”
approach to novelty. As for novelties, so for changes; evolutionary changes in phe-
notype space drives changes in genotype space: “genes are followers in evolution,
not leaders” [West-Eberhard, 2003].