Evolutionary Biology Volume 31, 2000, pp 155-217

Evolutionarily Stable Configurations: Functional Integration and the Evolution of Phenotypic Stability

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Abstract

Phenotypic evolution has been studied since Darwin established the fact of evolution. In contrast, molecular evolution has been a subject of study since the mid-1960s. Nevertheless, our understanding of the mechanisms of phenotypic evolution is far less developed than our knowledge of molecular evolution. This fact is often attributed to the greater “complexity” of phenotypic characters, although it is not always clear what complexity means. More specifically, there are two features of phenotypic evolution that make molecular and phenotypic evolution quite distinct problems. First, molecular evolution is a continuing process, often occurring over long periods of time at a nearly constant rate, even if there are variations in rate among lineages. In contrast, phenotypic evolution is perceived as a highly irregular process with long periods of stasis interrupted by short bursts of change (Gould and Eldredge, 1977; Kimura, 1983). Second, most phenotypic characters comprise many levels of organization from the molecular to the behavioral and the population level, and the rate of change is nonuniform across these levels of organization. Some attributes of the phenotype, such as color and size, vary widely and evolve rapidly whereas other aspects of the phenotype, such as mode of food acquisition, are remarkably stable. Furthermore, even the conservative elements of the phenotype are not immutable because they have evolved in ancestral lineages and may become variable in a descendant lineage. Molecular evolution, on the other hand, pertains to evolutionary change on only one level of organization.

authorship equally shared