Evolutionary constraints and genotype spaces
Evolutionary constraints and genotype spaces
An evolutionary constraint is a bias or limitation in genotypic or phenotypic variation that a biological system produces. Striking phenotypic examples include the absence of photosynthesis in higher animals, and the general lack of teeth in the lower jaw of frogs. Constraints can influence the spectrum of evolutionary adaptations and innovations that are accessible to living things. Based on the cause of constrained phenotypic variation, one can distinguish physicochemical, selective, genetic, and developmental constraints. The latter class of constraints emerges from the processes that produce phenotypes from genotypes. This chapter examines these four causes for molecules, regulatory circuits, and metabolic networks in the genotype space framework. This framework shows that processes of phenotype formation cause the three other classes of constraints. It can help us appreciate why causes of constrained variation are often entangled and not clearly separable. The chapter also shows that the kind of evolutionary stasis that occurs during punctuated and episodic evolution is a consequence of genetic constraints, whose origins the genotype space framework can readily explain.
Keywords: photosynthesis, evolutionary constraint, constrained variation, selective constraint, genetic constraint, developmental constraint, genotype space
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