Designed to address the major conceptual problems associated with evolution and variation and survival in populations, this module can be used with high school students or college nonscience majors including those in elementary education. It is one in a series developed by the project "Overcoming Critical Barriers to Learning in Nonmajors' Science Courses." The materials offer guidance to teachers in diagnosing student deficiencies, in creating dissatisfaction with misconceptions, and in providing opportunities for application and practice. This module contains: (1) an introduction (specifying the critical barriers to understanding natural selection and explaining how to use the module to overcome these barriers); (2) diagnostic test and commentary (designed to be used as a pretest and/or posttest); (3) materials for lecture or discussion with commentary (consisting of a series of copy-ready masters for use as overhead transparencies and student handouts on evolution by natural selection); (4) laboratory activities and commentary (including a lesson on the evolution of "bead bugs"); and (5) problem sets (addressing the value of variation of traits to the process of natural selection and the nature of adaptive traits). All instructional materials for the students are juxtaposed with instructor commentaries. (ML)