  The model organism approach faces challenges, however. As Schaffner recognizes, model organisms are also idealizations: organisms are selected for features not generalizable even to close relatives like rapid development, short generation time, small adult size, and insensitivity to environmental variation (Wimsatt 1998); strains are inbred to remove genetic diversity. Context-sensitivity diminishes expectations that similar mechanisms operate in simple and complex systems; multiple realizeability creates doubts that similar explanations will be found across taxa (Wimsatt 1998). Evolution is a branching process; as Richard Burian (1993) emphasizes: “At (virtually?) all levels of the biological world—including the biochemical—it is an open question how general the findings produced by the use of a particular organism are” (p. 365). Consequently, support for theoretical hypotheses requires the experimental findings to be placed within a comparative and evolutionary framework attentive to how widely the relevant nucleotide sequences and traits are distributed phylogenetically: “detailed knowledge of (historical) biological contingencies constrains—and ought to constrain—the evaluation of experimental work in biology and the knowledge claims based on that work” (Burian 1993, p.  366).[36]