196 D. M. Walsh
adaptive evolution too.
The ontogeny-first conception of evolution does not deny the existence of Dar-
win’s process. Selection, as it were, occurs spontaneously. One doesn’t need to add
a distinct population-level process to the mix to get adaptive evolution to occur.
We have all the ingredients we need in the development and reproduction of indi-
vidual organisms. Nor does one need to posit an independent, supra-organismal
causes of the adaptiveness of evolutionary change. Selection is a genuine process,
of course, perhaps even a causal process, but it doesn’t contribute any causes to
adaptive evolution that aren’t already fully accounted for by the development and
reproduction of individual organisms. The population-level Darwinian process —
even the increased in average adaptedness of organisms in a population — is just
the resultant of the suite of individual-level processes of development and repro-
duction. The sum of these processes isadaptiveevolution, because of the adaptive
capacities of organismal development.
On Grade III ontological commitment, the plasticity of development (plus some
reproduction) causes: (i) the reliable recurrence of traits from generation to gen-
eration (inheritance) (ii) the origin of adaptive novelties and (iii) the increase
in the adaptedness of organisms in a population to their conditions of existence
(adaptation). Ontogeny is the central unifying process in all of evolution.
5 CONCLUSION: GOING THROUGH THE GRADESI have attempted to outline a space of alternative views on the significance of
organismal development for the explanation of adaptive evolution. For the most
part biologists, philosophers of biology, and most certainly non-specialists in biol-
ogy labour under a conception evolution forged in the early days of the modern
synthesis, and then tempered by generations of selectionism. On this account,
development is of minor, sometimes negligible significance. There may be good
sociological, historical, even technological explanations of the marginalization of
development; perhaps it is harder to study development in detail than much of
paleontology, or ethology, or ecology, or systematics, or population genetics, or
any of the disciplines that coalesced into the synthesis. Certainly the current re-
naissance of developmental biology had to await a raft of technological advances
in molecular biology. Nevertheless, it is important to acknowledge that there are
conceptual reasons too. The fact that ontogeny plays only a peripheral role in evo-
lutionary biology is due to a commitment embodied in the predominant version
of modern synthesis biology to the fragmentation of evolution into three discrete,
largely autonomous processes: development, inheritance, and adaptation. This
fragmentation has consequences for the place of development in evolutionary biol-
ogy; it leads to the marginalization of development. But the fragmentation isn’t
obligatory.
I have outlined three grades of commitment to the significance of ontogeny to
the explanation of adaptive evolution. As we progress through the grades (from
Grade I to Grade III) we see two related trends (i) an increase in the significance