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This chapter focuses on assessing canalization and cryptic genetic variation. Regardless of the concerns with the mechanistic explanation of genetic assimilation, the plausibility of the phenomena of genetic assimilation as well as the existence of cryptic genetic variation were established via some empirical experiments. Waddington demonstrated that traits that were invariant under most (normal) environmental circumstances could be sensitized so as to express phenotypic variation for these traits. The classic example of Waddington's was the use of a high-temperature “heat-shock” in Drosophila, which resulted in some flies having lost their wing cross-veins. Waddington demonstrated that the cross-veinless phenotype could be selected upon, suggesting considerable hidden (cryptic) genetic variation for this trait. In considering the origin of developmental variation, one must consider the …