Developmental bias in evolution: evolutionary accessibility of phenotypes in a model evo-devo system.

The success of the modern synthesis has resulted in forces of evolutionary change other than natural selection being marginalized. However, recent work has attempted to show the importance of non-selective influences in shaping organic form. One such force is developmental bias, in which phenotypes are differentially produced. We use a simulation model of neural development to explore questions of general interest about developmental systems. From this analysis, we find that the pattern of developmental bias varies strongly with the genotype even among phenotypically-neutral genotypes. In addition to this genotype-dependent developmental bias (local bias), an intrinsic bias exists in the developmental system (global bias). We also show that developmental bias varies among related genotypes that produce the same phenotype. Finally, we illustrate how a pattern of bias emerges from the manner in which mutations affect the regulatory structure of the wild-type genotype. These results suggest that developmental bias could have a strong influence on the direction of evolutionary modification.