Stephen Stearns, teaching Yale's Evolution and Medicine course, examines why natural selection leaves the human body full of compromises rather than perfect design. Drawing on the textbook Evolutionary Medicine, he explains the concept of tradeoffs: traits that improve one function often worsen another, so selection settles on a balance rather than an optimum. Stearns works through examples of how reproduction, immune defense, and growth compete for finite resources, and how these competing demands shape vulnerability to disease. The lecture builds toward a definition of what a patient actually is from an evolutionary standpoint, framing illness not as a design flaw but as the byproduct of ancestral tradeoffs that once maximized reproductive success under different conditions. Delivered as a short, focused segment within a longer course, it gives a clear, plainly narrated account of one of evolutionary medicine's core explanatory tools.