40. Where does sleep fit in aging biology?

Sleep is still conceptually and mechanistically puzzling, but includes daily maintenance that supports brain and systemic homeostasis (metabolic reset, waste clearance, synaptic and immune recalibration). In the deleteriome framework, sleep limits exposure to some forms of damage-generating activity and supports restoration. An complementary model is that a sleep-like state is ancestral and sustained wakefulness is an evolved, functionally demanding state whose liabilities accumulate during activity.