The teacher first introduces the new model. Students then design and perform computational experiments to explore how selective advantage because of different behaviors (due to a physical trait – flagella number) affect the outcomes of natural selection in population of virtual bacteria. Students present their initial results to the class and the class discusses possible explanations for why these different conditions yield different shifts in the distribution of trait variations from natural selection. Groups return to their experimentation and develop their explanations further, and report these out at the end of their experimentation. At the end of class, the teacher develops class consensus on the big ideas regarding the conditions necessary for natural selection and revises the scientific principle from the last lesson.

This lesson uses the same model as the previous lesson of a population of bacteria with different types. However, there are some important differences. In this model, there is an advantage of having higher number of flagella and there is cost associated to having flagella. 

[Note: Computational scientists use variations of a model to study different but related phenomena. Though the model in this lesson looks similar to the one in previous lesson, it has important differences.]