Lab 17: Mechanisms of Evolution: Why Does a Specific Version of a Trait Become More Common in a Population Over Time? is one of a series of lab investigations for the middle school student from the book, “Argument-Driven Inquiry in Life Science: Lab Investigations for Grades 6-8”. Using the online NetLogo simulation, Bug Hunt Camouflage, students explore how the frequency of different versions of the body color of a bug causes a change in the population of bugs over time in two different environments. From this, they then develop a model that explains how the trait became more common in the population over several generations. Students then engage in argumentation with other groups in the classroom based on the data that they have collected from their investigation in the NetLogo simulation and their analysis of the data. “Checkout Questions” are provided to facilitate student reflection on what was learned. Students are assigned a short investigation report to finish processing their experience. Significant background information is provided for teachers and to a lesser degree in the student hand-out in the introduction. The standards addressed in the lesson are also included in the teacher’s notes.