New perspectives on the role of constraints in evolution

The course and outcome of biological evolution is strongly influenced by constraints. They, flanking the work of natural selection, operate not only by limiting but also by changing the evolutionary processes. The following constraint categories are discussed and analyzed: structural developmental, phylogenetic, genetic, epigenetic, behavioural, ecological (as ecosystemic) and selective. Epigenetic, behavioural and ecosystemic constraints may be important ways through which an environmental information, supplementary to that conveyed by natural selection, can flow in the evolutionary process influencing the phenotype construction. The different constraint categories depend on three basic evolutionary forces: structure, environment and history or contingency. They form a network of reciprocal dependences and interact with natural selection. In the newly proposed two-step evolutionary model (Sara [1993]), in which two phases alternate at each generation, the constructive, organismic phase is represented by constraints (except the selective ones) while the selective, populational phase is represented by natural selection and selective constraints as drift.