Introduction

In the last decade, the introduction of a developmental framework into the core of evolutionary theory has brought about a radical change in perspective. In the emerging synthesis, known as “evolutionary developmental biology” (or “evo devo”), the development of the phenotype, rather than the genetic variant, assumes a primary theoretical position, and is the point of departure for evolutionary analysis. Changes in development which lead to changed phenotypes are primary and the organism exhibiting an altered phenotype is the target of selection. Genes, as West-Eberhardt (2003) succinctly has put it, “are followers in evolution”: changes in gene frequencies follow, rather then precede, phenotypic changes that mainly arise as reactions to environmental changes. The focus of developmentally informed studies of evolution is therefore on processes of development that can generate evolutionary innovation, on the constraints and generic properties of developmental systems, on the architecture of developmental networks, and on the evolution of the ability to develop and learn (Gilbert 2003). It is clear today that in order to explain the evolution of a new trait – be it morphological, physiological, or behavioral – it is necessary to explain the evolution of the developmental processes that contribute to its construction during ontogeny. Therefore, processes leading to developmental flexibility and sensitivity to environmental variations on the one hand, and to the buffering of environmental and genetic “noise” on the other hand, are important subjects of empirical and theoretical research.