Chapter 12: Aging and Death

Sapolsky demonstrates that while older adults maintain relatively normal function under stable conditions, they experience disproportionate decline when exposed to stressors—struggling to regulate body temperature, recover from illness, sustain cardiovascular output during exertion, and maintain cognitive performance under time pressure. Aging is fundamentally characterized as a progressive erosion of physiological resilience. A central mechanism involves dysregulation of the hypothalamic-pituitary-adrenal axis: with advancing age, organisms fail to suppress stress hormone secretion efficiently, maintaining elevated baseline levels of glucocorticoids that remain chronically elevated after stressful events. This hormonal dysregulation drives accelerated tumor development, hypertension progression, and immunological decline. Extreme examples from salmon and marsupial mice exhibit programmed senescence triggered by runaway glucocorticoid secretion, demonstrating that stress hormones can directly drive rapid aging and death—a phenomenon operating more gradually but profoundly in mammals and humans. The hippocampus emerges as a critical nexus in this system: this brain region governs learning and memory while simultaneously providing negative feedback regulation of stress hormones. With age, cumulative lifetime glucocorticoid exposure damages hippocampal neurons, weakening their inhibitory control over the stress axis and creating a self-perpetuating cascade of elevated hormones and accelerated neurodegeneration. Although glucocorticoids do not directly kill neurons, they compromise metabolic resilience and increase vulnerability to secondary insults like hypoglycemia, ischemia, and seizures—a mechanism with profound implications for understanding age-related cognitive decline, dementia, and Alzheimer's disease. The chapter also addresses cultural dimensions of aging, contrasting Western medicalization and fear of mortality with traditional societies where elders are respected and death accepted with equanimity, illustrated through Sapolsky's ethnographic observations among the Masai. Ultimately, aging emerges not as inevitable passage of time but as cumulative biological, psychological, and social stress effects that determine aging trajectories and mortality.