Death is the end of an organism's life. It is the irreversible cessation of biological functions that sustain a living organism. Entropy, nature's tendency toward disorder, can contribute to the breakdown of living systems over time. Upon death, organisms stop exhibiting behavior and generally begin to decompose through various physical and chemical processes. Death can occur at any stage of development, including in infancy. A person may experience clinical death that is reversible, resulting in some cases in a near-death experience. In humans, establishing death of the brain determines that an individual has irreversibly died.
Natural selection of organisms which successfully pass on their genes to the next generation drives life to engage in a struggle for existence against death. Because of this, living things, including humans, normally fear death and have strong instincts to avoid it. Some organisms may kill other organisms, causing them to die through herbivory, predation, or parasitism in order to take resources from the bodies of other organisms into their own. Organisms can also kill others through competition, in which they struggle with each other for control of external resources. Sometimes, organisms will take resources from organisms which have already died, either through scavenging or decomposition. However, despite the widespread instinct to survive, sometimes animals may commit suicide, being intentionally self-caused death, which in humans may be attributed to a variety of risk factors including mental illness. Besides intentional killing, organisms can die due to failure to secure necessary resources such as starvation or dehydration, or through harmful physical factors such as natural disasters or diseases. Organisms that do not die for these reasons usually succumb to death from old age; however, some organisms, such as the immortal jellyfish, are biologically immortal while still being able to die from other causes. Organisms have varying life histories, with differing life spans between species. Death affects populations of organisms, with selective pressures resulting in organisms with traits that are unfavorable in a given environment to die off; changes to an environment such as climate change or invasive species can cause entire ecosystems to die at higher rates than usual. As opposed to intentional suicide, sometimes species will commit evolutionary suicide in which existing adaptations lead to the deaths of all of their members. When all individuals of a clade have died, that clade is said to be extinct. Extinction events are periods of time when rates of extinction on Earth result in global loss of biodiversity due to mass death within many species worldwide.
As human beings have evolved the mental faculties to be aware of death, knowledge of death is a central part of the human condition and therefore is universal to human culture. Knowledge of death has motivated the development of a variety of religious, spiritual, ethical, and legal methods for understanding and responding to it. Many cultures have a concept of the survival of individuals after death, whether in an afterlife, as spirits, or through reincarnation. While such dualistic notions of survival past death are common to the world's major religions, other monist forms of thought such as materialism and physicalism generally maintain that death is the irreversible end of personal identity. Some societies have taboos on the dead, whereby information about a person who has died is censored. To avoid death, people have sometimes sought to achieve immortality, or eternal life, such as through cryogenics. Once a person has died, their community will generally perform funerary rituals to process the cadaver and honor the decedent according to practices specific to their culture. If a person is understood to have most likely died without direct evidence, they can be legally declared dead in absentia in many countries. Surviving people close to a decedent normally experience grief, a set of powerful mental and emotional processes associated with the loss of the person. For a human being to kill another is called homicide, an act that has profound legal implications in most societies. Homicide considered unjustified is known as murder, and is generally considered one of the most serious crimes in any society. However, states claim a monopoly on violence by which they may legally kill people, whether as punishment for crimes, through police violence, or through war. The study of death is known as thanatology.
Background
As of the early 21st century, 56 million people die per year. As of 2022, an estimated total of almost 110 billion humans have died, or roughly 94% of all humans to have ever lived. The cause of death is usually considered important, and an autopsy can be done to determine it. There are many causes, from accidents to diseases or crime and war. The most common reason is aging; the most common cause is cardiovascular disease (CVD), which is a disease that affects the heart or blood vessels. A substudy of gerontology known as biogerontology seeks to eliminate death by natural aging in humans, often through the application of natural processes found in certain organisms. However, as humans do not have the means to apply this to themselves, they have to use other ways to reach the maximum lifespan for a human, often through lifestyle changes, such as calorie reduction, dieting, and exercise. The idea of lifespan extension is considered and studied as a way for people to live longer.
Determining when a person has definitively died has proven difficult. Initially, death was defined as occurring when breathing and the heartbeat ceased, a status still known as clinical death. However, the development of cardiopulmonary resuscitation (CPR) meant that such a state was no longer strictly irreversible. For all organisms with a brain, death can instead be focused on this organ. Brain death was then considered a more fitting option, but several definitions exist for this: some people believe that all brain functions must cease; others believe that even if the brainstem is still alive, the personality and identity are irretrievably lost, so therefore the person should be considered entirely dead. Brain death is sometimes used as a legal definition of death.
There are different customs for honoring the lifeless body, such as a funeral, cremation, or sky burial. After a death, an obituary may be posted in a newspaper, and the family and friends of the dead person usually go through the grieving process.
Definition
There are many scientific approaches and various interpretations of the concept. Additionally, the advent of life-sustaining therapy and the numerous criteria for defining death from both a medical and legal standpoint have made it difficult to create a single unifying definition.
Defining life to define death One of the challenges in defining death is in distinguishing it from life. As a point in time, death seems to refer to the moment when life ends. Determining when death has occurred is difficult, as cessation of life functions is often not simultaneous across organ systems. Such determination, therefore, requires drawing precise conceptual boundaries between life and death. This is difficult due to there being little consensus on how to define life.
It is possible to define life in terms of consciousness. When consciousness ceases, an organism can be said to have died. One of the flaws in this approach is that there are many organisms that are alive but probably not conscious. Another problem is in defining consciousness, which has many different definitions given by modern scientists, psychologists and philosophers. Additionally, many religious traditions, including Abrahamic and Dharmic traditions, hold that death does not (or may not) entail the end of consciousness. In certain cultures, death is more of a process than a single event. It implies a slow shift from one spiritual state to another.
Other definitions for death focus on the character of cessation of organismic functioning and human death, which refers to irreversible loss of personhood. More specifically, death occurs when a living entity experiences irreversible cessation of all functioning. As it pertains to human life, death is an irreversible process where someone loses their existence as a person.
Definition of death by heartbeat and breath Historically, attempts to define the exact moment of a human's death have been subjective or imprecise. Death was defined as the cessation of heartbeat (cardiac arrest) and breathing, but the development of CPR and prompt defibrillation have rendered that definition inadequate because breathing and heartbeat can sometimes be restarted. This type of death where circulatory and respiratory arrest happens is known as the circulatory definition of death (CDD). Proponents of the CDD believe this definition is reasonable because a person with permanent loss of circulatory and respiratory function should be considered dead. Critics of this definition state that while cessation of these functions may be permanent, it does not mean the situation is irreversible because if CPR is applied fast enough, the person could be revived. Thus, the arguments for and against the CDD boil down to defining the actual words "permanent" and "irreversible," which further complicates the challenge of defining death. Furthermore, events causally linked to death in the past no longer kill in all circumstances; without a functioning heart or lungs, life can sometimes be sustained with a combination of life support devices, organ transplants, and artificial pacemakers.
Brain death
Today, where a definition of the moment of death is required, doctors and coroners usually turn to "brain death" or "biological death" to define a person as being dead; people are considered dead when the electrical activity in their brain ceases. It is presumed that an end of electrical activity indicates the end of consciousness. Suspension of consciousness must be permanent and not transient, as occurs during certain sleep stages, and especially a coma. In the case of sleep, electroencephalograms (EEGs) are used to tell the difference.
The category of "brain death" is seen as problematic by some scholars. For instance, Dr. Franklin Miller, a senior faculty member at the Department of Bioethics, National Institutes of Health, notes: "By the late 1990s... the equation of brain death with death of the human being was increasingly challenged by scholars, based on evidence regarding the array of biological functioning displayed by patients correctly diagnosed as having this condition who were maintained on mechanical ventilation for substantial periods of time. These patients maintained the ability to sustain circulation and respiration, control temperature, excrete wastes, heal wounds, fight infections and, most dramatically, to gestate fetuses (in the case of pregnant "brain-dead" women)."
While "brain death" is viewed as problematic by some scholars, there are proponents of it that believe this definition of death is the most reasonable for distinguishing life from death. The reasoning behind the support for this definition is that brain death has a set of criteria that is reliable and reproducible. Also, the brain is crucial in determining our identity or who we are as human beings. The distinction should be made that "brain death" cannot be equated with one in a vegetative state or coma, in that the former situation describes a state that is beyond recovery.
EEGs can detect spurious electrical impulses, while certain drugs, hypoglycemia, hypoxia, or hypothermia can suppress or even stop brain activity temporarily; because of this, hospitals have protocols for determining brain death involving EEGs at widely separated intervals under defined conditions.
Neocortical brain death