Facilitated variation

The theory of facilitated variation demonstrates how seemingly complex biological systems can arise through a limited number of regulatory genetic changes, through the differential re use of pre existing developmental components. The theory was presented in 2005 by Marc W. Kirschner (a professor and chair at the Department of Systems Biology, Harvard Medical School) and John C. Gerhart (a professor at the Graduate School, University of California, Berkeley). The theory of facilitated variation addresses the nature and function of phenotypic variation in evolution. Recent advances in cellular and evolutionary developmental biology shed light on a number of mechanisms for generating novelty. Most anatomical and physiological traits that have evolved since the Cambrian are, according to Kirschner and Gerhart, the result of regulatory changes in the usage of various conserved core components that function in development and physiology. Parter et al. (the Baldwin effect), Ivan Schmalhausen, Conrad Waddington (genetic assimilation and accommodation), and Mary Jane West Eberhard (‘genes are followers not leaders’). More recently, the theory of facilitated variation has been embraced by advocates of an extended evolutionary synthesis, and emphasized for its role in generating non random phenotypic variation (‘developmental bias’). However, some evolutionary biologists remain skeptical as to whether facilitated variation adds a great deal to evolutionary theory.

Creationists and advocates of Intelligent Design have argued that complex traits cannot evolve through successive small modifications to pre existing functional systems. The theory of facilitated variation challenges this idea of irreducible complexity by explaining how random mutation can cause substantial and adaptive changes within a species. It explains how the individual organism can change from a passive target of natural selection, to an active player in the 3 billion year history of evolution. Kirschner and Gerhart's theory thereby provides a scientific rebuttal to modern critics of evolution who champion Intelligent Design.