192 D. M. Walsh
defining property of whole organisms, a property that is most clearly manifested
in development. This brings us to our third grade of ontogenetic involvement.
4.3 Grade III: Development as Adaptive
The distinguishing feature of Third Grade ontogenetic involvement is its rejection
of sub-organismal biology. In Grades I and II the distinctive capacities of organisms
play no significant role in explaining inheritance, development and adaptation. In
Grade III the capacities of organisms explain and unify all three processes. Evelyn
Fox Keller characterizes an organism in the following way:
It is a bounded physico-chemical body capable not only of self-regulation
— self-steering — but also, and perhaps most important, of self-forming.
An organism is a material entity that is transformed into a self-generating
“self” by virtue of its peculiar and particular organization. [Fox Keller,
2000, 108]Organisms are adaptive entities, capable of attaining their developmental end
states, and maintaining their viability in the face of all manner of vagaries of their
environment, genome and developmental systems [Gibson, 2002]. They are the
very paradigm of a robust self-organizing system ([Kitano, 2004]; [Goodwinet al.,
1993]).
The definitive feature of organisms is phenotypic plasticity, ‘a universal prop-
erty of living things’ [West-Eberhard, 2003]. Plasticity is ‘...the ability of an
organism to react to an internal or external environmental input with a change
in form, state, movement, or rate of activity’ [West-Eberhard, 2003, 33]. Recent
work in development suggests that phenotypic plasticity confers on organisms both
stability and mutability. The stability of organisms is achieved through their ca-
pacity to make compensatory changes in their physiology and development to
perturbations. Plasticity also endows organisms with the capacity to respond to
unpredictable circumstances through the initiation of entirely novel, yet stable
phenotypes. Plasticity, then, fulfilsbothconditions for evolvability.
Mary Jane West-Eberhard has proposed that adaptive evolution, and diversi-
fication, are driven primarily by the control that the plasticity of the phenotype
exerts over the constituent processes of an organism’s development. Adaptive
evolution proceeds in three stages stages (i) phenotypic accommodation, (ii) de-
velopmental recombination and (iii) genetic accommodation, all of which depend
upon the plasticity of organisms.^14
Phenotypic accommodation: Plasticity allows organisms to accommo-
date to the features of their environment (and their genomes) in ways
that preserve their well functioning, by making subtle compensatory
adjustments to their phenotypes. “Phenotypic accommodation due to(^14) In her 2003 West-Eberhard explicitly sites two stages; in her 2005b paper there appear to
be three.