Stephen Stearns, teaching Yale's Evolution and Medicine course, asks what aging looks like when you treat the patient as a product of natural selection rather than just a biological machine wearing out. Drawing on the textbook Evolutionary Medicine, he lays out why senescence exists at all from an evolutionary standpoint, why selection pressure weakens on traits that only matter after reproduction, and how tradeoffs between early reproduction and late-life decline get built into an organism's life history. The lecture is part of a numbered series, and this segment focuses specifically on aging as a case study for the evolutionary framework the course applies throughout. Stearns keeps the argument tight and concept-driven, aimed at students who already have the course's basic vocabulary of fitness, selection, and tradeoffs. Seventeen minutes, lecture-hall delivery, no slides described but content-dense.