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Table 1 Outline of the sections of the Darwinian Snails modules in both versions

From: Iterative design of a simulation-based module for teaching evolution by natural selection

Exercise name in workbook version Section name in tutorial version Description (tutorial version)
Prelude 1. Snail shells Introduces students to the study system and to histograms as a way of graphing data to visualize the distribution of trait variation in a population
1. A model of evolution by natural selection 2. Evolution by natural selection Students play the role of a crab preying on snails. They discover that thinner-shelled snails are easier to eat and go through several rounds of selection and reproduction to see a shift in the trait distribution in the population, thus visualizing natural selection in action
2. The requirements for evolution by natural selection
3. Darwin’s theory of evolution by natural selection
3. Requirements for natural selection Students turn off three conditions for evolution by natural selection in turn to see the effect of each: variability; heritability; and differential survival. In turning off differential survival, students also see genetic drift in the small population. Mutations are disabled in this section
4. The source of variation among individuals
5. What makes populations evolve?
4. The source of variation The students can now see the effect of mutations in the population. Starting with a snail population with reduced trait variation, students “turn on” mutations and examine parent/offspring combinations and histograms to see whether mutations are directional in the presences and absence of crab predation
6. Challenge: evolution by natural selection in flat periwinkles 5. Testing for natural selection
6. Extension: experimenting with snails
Data from Seeley (1986) are shown and students are asked to interpret the data
Students are asked to devise their own experiments to determine whether the conditions for evolution by natural selection are met in a snail population
  1. Rows correspond to sections in the tutorial; descriptions are of tutorial sections. The overall flow of the module is the same in both versions, but the way the material is divided into sections differs, so that some sections in the tutorial include material from more than one section of the workbook, and vice versa. In the final dataset discussed in this study (study 2), the tutorial version no longer included the Extension Sect. (6)—that material was moved to a separate module that was not part of this study