title: Evolutionary constraints or opportunities?
abstract: Natural selection is traditionally viewed as a leading factor of evolution, whereas variation is assumed to be random and non-directional. Any order in variation is attributed to epigenetic or developmental constraints that can hinder the action of natural selection. In contrast I consider the positive role of epigenetic mechanisms in evolution because they provide organisms with opportunities for rapid adaptive change. Because the term "constraint" has negative connotations, I use the term "regulated variation" to emphasize the adaptive nature of phenotypic variation, which helps populations and species to survive and evolve in changing environments. The capacity to produce regulated variation is a phenotypic property, which is not described in the genome. Instead, the genome acts as a switchboard, where mostly random mutations switch "on" or "off" preexisting functional capacities of organism components. Thus, there are two channels of heredity: informational (genomic) and structure-functional (phenotypic). Functional capacities of organisms most likely emerged in a chain of modifications and combinations of more simple ancestral functions. The role of DNA has been to keep records of these changes (without describing the result) so that they can be reproduced in the following generations. Evolutionary opportunities include adjustments of individual functions, multitasking, connection between various components of an organism, and interaction between organisms. The adaptive nature of regulated variation can be explained by the differential success of lineages in macro-evolution. Lineages with more advantageous patterns of regulated variation are likely to produce more species and secure more resources (i.e., long-term lineage selection).
authors.affiliation: National Institute on Aging, Genetics Laboratory, 251 Bayview Blvd., Baltimore, MD 21224, USA. Electronic address: sharoval@mail.nih.gov.
authors.forename: Alexei A
authors.initials: AA
authors.lastname: Sharov
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics*; D000818:Animals; D017753:Ecosystem; D004777:Environment; D044127:Epigenesis, Genetic; D019143:Evolution, Molecular; D014644:Genetic Variation / Q000235:genetics*; D016678:Genome / Q000235:genetics; D006801:Humans; D008957:Models, Genetic; D010641:Phenotype; D012641:Selection, Genetic / Q000235:genetics*
keywords: Developmental correlation; Multitasking; Phenotypic plasticity; Regulated variation; Units of selection, macro-evolution