 Although this tension obtains even if the focus is not on evolutionary questions, sometimes encouraging developmental biologists to interpret absence of evidence as evidence of the developmental insignificance of phenotypic plasticity, it is exacerbated for evolutionary researchers. The documentation of patterns of variation is precisely what is required to gauge the evolutionary significance of phenotypic plasticity. Practices of developmental staging in model organisms can retard our ability to make either a positive or negative assessment. Developmental staging, in conjunction with the properties of model organisms, tends to encourage a negative assessment of the evolutionary importance of phenotypic plasticity because the variation is not manifested and documented, and therefore is unlikely to be reckoned as substantive. Idealizations involving normal stages discourage a robust experimental probing of phenotypic plasticity, which is an obstacle to determining its evolutionary significance.