The purpose of this study is to explore community college students' reasoning patterns and argumentation within the context of natural selection. Written assessments and interviews were administered to 2-year college students. Participants were given the Lawson Classroom Test of Scientific Argumentation (LCTSR), a Test of Scientific Argumentation (TSA), and an Open Response Questionnaire (ORQ). The LCTSR and TSA were used to provide insight into student reasoning abilities and students' understanding of the logical structure of arguments. Significant correlations were found between categories of the LCTSR and TSA, indicating that students' reasoning and argumentation are connected. The ORQ was used to prove students' understanding of concepts in natural selection and how they reason through data and coordinate prior knowledge and evidence to develop claims. The interviews were used to analyze how students justify their claims. Results from the ORQ show that students in this sample struggled with identifying, understanding, and using warrants. Additionally, when considering a counterargument and justifying claims, students always set grounds of an argument, rather than critically analyzing the structure or content of counterarguments. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]