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Novelty in Evolution: Restructuring the Concept (Muller, Wagner, 1991)

Gerd B. Muller, Gunter P. Wagner

"According to this hypothesis, the first rudiments of morphological novelties appear as neutral by-products of evolutionary alterations to developmental processes. The causality for their appearance is thus proposed to lie in the system properties of development, which can transform gradual and quantitative evolution into qualitative phenotypic effects."

"the available data strongly suggest that side effects of developmental organization represent the kernel of morphological novelty."

"A preliminary overview of the developmental modes associated with the origination of novelties point to the central role of heterochrony as the primary initiating factor. Heterochrony alone, however, can only modify processes that are already established."

JLJ - What a novel idea... if you have a process which produces a living organism, all you have to do to produce a novelty is to tinker with that development process, over time. Delay a certain step here, enhance another particular step there, the existing developmental process itself carries the "tinkered result" to a completion, producing a "maybe better, maybe not" creature. "Selection" will determine whether the novelty keeps contributing to the gene pool.

Clearly, for game theory the concept of heterochrony is critical. From Wikipedia, in biology, heterochrony is defined as a developmental change in the timing or rate of events, leading to changes in size and shape. There are two main components, namely (i) the onset and offset of a particular process, and (ii) the rate at which the process operates.

By delaying the investigation of certain non-critical paths or paths intelligently determined to be without reasonable potential to "turn around" to favor the opposing side, in favor of investigating those other paths with possible impact on the adaptive capacity of the position to remain coercive, we effectively use time wisely in estimating how "preadapted" potential game moves/positions are to the conflicted unfolding of the interaction network that presently exists. We "choose" a move, yes, but we do that by intelligently and strategically estimating/assessing/guessing the potential to coerce - an intelligent investigation and assessment of that potential lies behind our "decision" of one move over the other. Lindblom (1979) completes the concept by suggesting that we can "decide" without understanding (!): "social problems can often be attacked... by 'resultants' of interaction rather than 'decisions' arising out of anyone's understanding of the problem at hand.... Understanding a social problem is not always necessary for its amelioration - a simple fact still wisely overlooked."

p.229 the difficulty of how new characters could arise from a process of gradual variation and selection was at the center of the early critique of Darwin's theory

p.230 the primary objective of this chapter is to liberate the novelty issue from its historical burden and to provide a new conceptual foundation for its analysis... We restrict our analysis here to the origin of new structures in morphological evolution.

p.231 We concentrate on the generative aspect of morphological innovations in the process of evolution.

p.234 heterochrony - phylogenetic changes in the timing and rates of ontogenetic processes.

p.235 Wake & Roth (106) suggest that novelties are generated through ontogenetic repatterning. Ontogenetic repatterning refers to the establishment of new sets of morphogenetic processes through disassociation and recombination of compartmentalized subsets of the developmental system.

p.235 Another approach is based on the system properties of development (64). According to this concept, heterochronic and nonheterochronic mechanisms of evolution have a quantitatively modifying effect on developmental parameters, but the magnitude of these modifications is limited by system-specific thresholds... The threshold origin and the embryonic preexistence of novel structures is thought to underlie their often rapid phenotypic appearance in a phylogenetic lineage. According to this hypothesis, the first rudiments of morphological novelties appear as neutral by-products of evolutionary alterations to developmental processes. The causality for their appearance is thus proposed to lie in the system properties of development, which can transform gradual and quantitative evolution into qualitative phenotypic effects.

p.236 Buss... considered the origin of novelties as resulting from conflicts between levels of selection.

p.236 We intend here to set the stage for a reformulation of the problem of novelties.

p.245 Here we identify particular properties of developmental systems that could promote the origination of novelty. Our approach, however, resides in a strictly neo-Darwinian frame, assuming that morphological evolution proceeds through gene substitutions that primarily affect cell behavior in developmental processes, leading primarily to changes in relative proportions and positions of embryonic characters. If these classic processes can produce novelties in the anatomical structure of organisms, one is led to hypothesize that the causality for their appearance lies in very basic and general properties of developmental systems that are affected by gene substitutions.

p.248 a change of context, initiated by temporal or spatial shifts, can lead to the formation of novel morphologies on the basis of preexisting interactive capacities. The historically established networks of developmental interactivity... thus not merely constrain morphological evolution, they also represent an important generative source for the origination of new structures.

p.249 Only recently, however, has it been proposed that threshold effects may represent a generative factor in the origination of morphological novelties (64, 66).

Developmental thresholds can lie in molecular and physical parameters of pattern formation, in critical cell number or blastema size, in inductive or spatial relationships, in physiological or biomechanical factors, etc.

p.251 The origin of new body plans requires the origin of morphological novelties, but it also requires the integration of this new character with the other parts of the organism. In this context it is irrelevant whether integration is due to functional necessities or due to epigenetic interdependencies. What counts is that some characters acquire an indispensable biological role that causes their conservation in spite of changing adaptive pressures.

p.252 It is unlikely that explanations for the origin of morphological novelties can be successful without the inclusion of the generative properties of developmental systems.

p.252 A preliminary overview of the developmental modes associated with the origination of novelties point to the central role of heterochrony as the primary initiating factor. Heterochrony alone, however, can only modify processes that are already established. The specific morphological composition of novelties that arise as a consequence of heterochronic alterations of a developmental process will depend in the particular organization of the developmental network of which the process is a part.

p.252 In general, however, the available data strongly suggest that side effects of developmental organization represent the kernel of morphological novelty.