This video guide prompts students thinking on the fabulous PBS documentary "Great Transformations". This documentary explores the way in which life has changed over time due to natural selection. This particular video explores the defining features of mammals, how a group of land mammals evolved into whales, and how a group of lobe-finned fish evolved into tetrapods. The "Great Transformations" video is available via public link online. The video guide includes a link to the accompanying video.