On average, the residents of Sun City, Arizona, occupy their domiciles for a dozen years. When they depart—almost always by dying—they often leave their brains behind. The stages of physical and mental decline take them from their dream house to a hospital off Del Webb Boulevard, then to a nursing home, and finally back to the medical complex, where researchers harvest their most important organ. Hoping to do good for science, they have enrolled in the Brain and Body Donation Program of the Banner Sun Health Research Institute—widely considered the world’s preeminent brain bank.