Fig. 5

In the Speciation module, students investigate two populations of Rhagoletis flies that are potentially diverging into two species. The “Hawthorns to Apples” video (left) introduces the example. In the paper-based “New Host, New Species?” activity, groups of students analyze data about life cycles, host fruit preference, and allele frequencies. The Speciation Organizer (right) helps students organize their evidence and evaluate it according to four criteria for speciation: reproductive isolation, differential selection, hybrid viability, and allele mixing. Students then argue whether the populations are one species or two, or somewhere in between