This exercise serves as the transition from guided work to more independent experimental reasoning.

Learning goals​

• synthesize ideas from the earlier exercises
• justify claims with patterns in collected evidence
• prepare for student-directed investigation

Step-by-step flow​

1. Start with the workspace saved from Exercise 3 or the provided workspace download so everyone begins from the same batch of organisms.
2. Reduce the selection pressure (penalty/reward) while keeping mutation constant.
3. Watch how the population drifts or stabilizes over the same number of steps.
4. Ask: which observed patterns can you attribute to drift versus selection? Support your answer with histogram snapshots or data exports.

Suggested use​

Use this near the end of the guided sequence, especially if students will move into an open-ended project afterward.

What students do​

• examine a contrast case where selection is reduced or absent
• refine claims about what selection does and does not explain
• prepare to design their own follow-up questions

Legacy lab-book framing​

The legacy lab book used this exercise to explore Population Change without Selection, providing a contrast case that helps students refine what selection does and does not explain.

Supporting materials​

• Exercise 4 PDF
• Exercise 4 workspace file
• Legacy explainer videos are part of the archived tutorial playlist; add them to docs/videos with transcript-first pages so students can still revisit the contrast cases without requiring the old flash interface.

Estimated time​

One class period for the activity, plus additional time if students are expected to develop project ideas immediately afterward.