This lesson was created by Dr. Jaimi Gray and the Non-Clinical Tomography Users Research Network (NoCTURN) Education and Outreach Community. It uses 3D models of vertebrate limb bones produced as part of the open Vertebrate (oVert) project to address the Natural Selection section of the middle school Next Generation Science Standards. 3D models are made from computed tomography (CT) scans of vertebrate forelimbs to enhance and illustrate the concept of homologous structures, and the evolution of anatomical structures as a function of their use (i.e. locomotion, food consumption). Activity should take approximately 100 minutes to complete (two 50 minute lessons). Includes a range of options to download or view 3D models for different classroom situations.