Death is the termination of the biological functions that define a living organism. It refers both to a particular event and to the condition that results thereby. The true nature of the latter has, for millennia, been a central concern of the world's religious traditions and of philosophical inquiry. Belief in some kind of afterlife or rebirth is a central aspect of many religious traditions.Humans and the vast majority of other animals die in due course from senescence. Remarkable exceptions include the hydra, and the jellyfish turritopsis nutricula, which is thought to possess in effect biological immortality.
Intervening phenomena which commonly bring about death earlier include malnutrition, disease, or accidents resulting in terminal physical injury. Predation is a cause of death for many species. Intentional human activity causing death includes suicide, homicide, and war. Roughly 150,000 people die each day across the globe. Death in the natural world can also occur as an indirect result of human activity: an increasing cause of species depletion in recent times has been destruction of ecosystems as a consequence of the widening spread of industrial technology.
Physiological death is now seen as less an event than a process: conditions once considered indicative of death are now reversible. Where in the process a dividing line is drawn between life and death depends on factors beyond the presence or absence of vital signs. In general, clinical death is neither necessary nor sufficient for a determination of legal death. A patient with working heart and lungs determined to be brain dead can be pronounced legally dead without clinical death occurring. Precise medical definition of death, in other words, becomes more problematic, paradoxically, as scientific knowledge and technology advance.
