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In the Light of Evolution, Volume I: Adaptation and Complex Design
of conserved components and processes to give phenotypic variations and selected traits. Regulatory change acts on the repertoire of unchanging core processes to select subsets, which are then externally selected upon. The burden of creativity in evolution, down to minute details, does not rest on selection alone. Through its ancient repertoire of core processes, the current phenotype of the animal determines the kind, amount, and viability of phenotypic variation the animal can produce in response to regulatory change. Thanks to the nature of the processes, the range of possible anatomical and physiological variations is enormous, and many are likely nonlethal, in part simply because the processes have been providing “useful” function since pre-Cambrian times. Phenotypic plasticities, both those evokable by environmental change and those developmental adaptabilities not evocable, are rich sources and favored paths of variation requiring little regulatory change.
These views are not at all Lamarckian, nor does facilitated phenotypic variation require selection for future good. Such facilitation arose, we think, as a by-product of the evolution of the special properties of the core processes, namely, of their robustness, adaptability, modularity, exploratory behavior, and capacity for weak regulatory linkage. These properties were probably selected at the level of the individual, simply for their capacity to make core processes work effectively under fluctuating external and internal conditions (Gerhart and Kirschner, 1997; Kirschner and Gerhart, 2005). In this way, the same molecular features that facilitate physiological and developmental change in an organism’s lifetime also facilitate evolutionary change in the long run, as regulatory changes become genetically fixed.