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A framework is presented in which the role of developmental rules in phenotypic evolution can be studied for some simple situations. Using two different implicit models of development, characterized by different developmental maps from genotypes to phenotypes, it is shown by simulation that developmental rules and drift can result in directional phenotypic evolution without selection. For both models the simulations show that the critical parameter that drives the final phenotypic distribution is the cardinality of the set of genotypes that map to each phenotype. Details of the developmental map do not matter. If phenotypes are randomly assigned to genotypes, the last result can also be proved analytically.