   Developmental processes may limit the spectrum of evolutionary trajectories available to a lineage.  Maynard Smith et al. (1985, page 266) defined a developmental constraint as “a bias on the production of variant phenotypes or a limitation on phenotypic variability caused by the structure, character, composition, or dynamics of the developmental system.” More recently, the definition of constraint has become more nuanced (see, e.g., Wagner and Altenberg 1996, Winther 2001).