Death

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Overview

Death is when signs of life in an organism cease. It refers both to a specific event and, particularly in humans, to a condition the true nature of which it has for millennia been a central concern of the world's religious traditions to penetrate.^[1] Numerous factors can cause death: predation, disease, habitat destruction, senescence, conflict, malnutrition, for example, or mere accidents resulting in terminal physical injury. Principal cause of death in people in developed countries is disease precipitated by aging.^[1] The chief concern of medicine has been to postpone and avert death. Precise medical definition of death, however, becomes more problematical, paradoxically, as scientific knowledge and technology advance.

Biology

Fate of dead organisms

In animals, small movements of the limbs (for example twitching legs or wings) known as a postmortem spasm can sometimes be observed following death. Pallor mortis is a postmortem paleness which accompanies death due to a lack of capillary circulation throughout the body. Algor mortis describes the predictable decline in body temperature until ambient temperature is reached. Within a few hours of death rigor mortis is observed with a chemical change in the muscles, causing the limbs of the corpse to become stiff (Latin rigor) and difficult to move or manipulate. Assuming mild temperatures, full rigor occurs at about 12 hours, eventually subsiding to relaxation at about 36 hours; however, decomposition is not always a slow process. Fire, for example, is the primary mode of decomposition in most grassland ecosystems.^[1]

Some organisms have hard parts such as shells or bones which may fossilize before decomposition can occur. Fossils are the mineralized or otherwise preserved remains or traces (such as footprints) of animals, plants, and other organisms. Fossils vary in size from microscopic, such as single cells, to gigantic, such as dinosaurs. A fossil normally preserves only a small portion of the deceased organism, usually that portion that was partially mineralized during life, such as the bones and teeth of vertebrates, or the chitinous exoskeletons of invertebrates. Preservation of soft tissues, such as in mummification, is extremely rare in the fossil record.

Competition, natural selection and extinction

Main articles: Competition (biology), natural selection, and extinction

Death is an important part of the process of natural selection. Organisms that are less adapted to their current environment than others are more likely to die having produced fewer offspring, reducing their contribution to the gene pool of succeeding generations. Weaker genes are thus eventually bred out of a population, leading to processes such as speciation and extinction. It should be noted however that reproduction plays an equally important role in determining survival, for example an organism that dies young but leaves many offspring will have a much greater Darwinian fitness than a long-lived organism which leaves only one.

Extinction

Extinction is the cessation of existence of a species or group of taxa, reducing biodiversity. The moment of extinction is generally considered to be the death of the last individual of that species (although the capacity to breed and recover may have been lost before this point). Because a species' potential range may be very large, determining this moment is difficult, and is usually done retrospectively. This difficulty leads to phenomena such as Lazarus taxa, where a species presumed extinct abruptly "reappears" (typically in the fossil record) after a period of apparent absence.

Through evolutional theory, new species arise through the process of speciation — where new varieties of organisms arise and thrive when they are able to find and exploit an ecological niche — and species become extinct when they are no longer able to survive in changing conditions or against superior competition. A typical species becomes extinct within 10 million years of its first appearance,^[1] although some species, called living fossils, survive virtually unchanged for hundreds of millions of years. Only one in a thousand species that have existed remain today.^[1][1]

After death an organism's remains become part of the biogeochemical cycle. Animals may be consumed by a predator or scavenger. Organic material may then be further decomposed by detritivores, organisms which recycle detritus, returning it to the environment for reuse in the food chain. Examples include earthworms, woodlice and dung beetles. Microorganisms also play a vital role, raising the temperature of the decomposing material as they break it down into simpler molecules. Not all material need be decomposed fully however; for example coal is a fossil fuel formed in swamp ecosystems.

Evolution of aging

Main article: Evolution of aging

Enquiry into the evolution of aging aims to explain why almost all living things weaken and die with age (a notable exception being hydra, which may be biologically immortal). The evolutionary origin of senescence remains one of the fundamental puzzles of biology.

In medicine

Definition

Historically, attempts to define the exact moment of death have been problematic. Death was once defined as the cessation of heartbeat (cardiac arrest) and of breathing, but the development of CPR and prompt defibrillation have rendered that definition inadequate because breathing and heartbeat can sometimes be restarted. This is now called "clinical death". Events which were 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.

Today, where a definition of the moment of death is required, doctors and coroners usually turn to "brain death" or "biological death": People are considered dead when the electrical activity in their brain ceases (cf. persistent vegetative state). It is presumed that a stoppage of electrical activity indicates the end of consciousness. However, suspension of consciousness must be permanent, and not transient, as occurs during certain sleep stages, and especially a coma. In the case of sleep, EEGs can easily tell the difference. Identifying the moment of death is important in cases of transplantation, as an organ for transplant must be harvested as quickly as possible after the death of the body.

The possession of brain activities, or ability to resume brain activity, is a necessary condition to legal personhood in the United States. "It appears that once brain death has been determined … no criminal or civil liability will result from disconnecting the life-support devices." (Dority v. Superior Court of San Bernardino County, 193 Cal.Rptr. 288, 291 (1983))

Those people maintaining that only the neo-cortex of the brain is necessary for consciousness sometimes argue that only electrical activity there should be considered when defining death. Eventually it is possible that the criterion for death will be the permanent and irreversible loss of cognitive function, as evidenced by the death of the cerebral cortex. All hope of recovering human thought and personality is then gone given current and foreseeable medical technology. However, at present, in most places the more conservative definition of death — irreversible cessation of electrical activity in the whole brain, as opposed to just in the neo-cortex — has been adopted (for example the Uniform Determination Of Death Act in the United States). In 2005, the case of Terri Schiavo brought the question of brain death and artificial sustenance to the front of American politics.

Even by whole-brain criteria, the determination of brain death can be complicated. EEGs can detect spurious electrical impulses, while certain drugs, hypoglycemia, hypoxia, or hypothermia can suppress or even stop brain activity on a temporary basis. Because of this, hospitals have protocols for determining brain death involving EEGs at widely separated intervals under defined conditions.

Misdiagnosed death

There are many anecdotal references to people being declared dead by physicians and then 'coming back to life', sometimes days later in their own coffin, or when embalming procedures are just about to begin. Owing to significant scientific advancements in the Victorian era, some people in Britain became obsessively worried about living after being declared dead.^[1]

A first responder is not authorized to pronounce a patient dead. Some EMT training manuals specifically state that a person is not to be assumed dead unless there are clear and obvious indications that death has occurred.^[1] These indications include mortal decapitation, rigor mortis (rigidity of the body), livor mortis (blood pooling in the part of the body at lowest elevation), decomposition, incineration, or other bodily damage that is clearly inconsistent with life. If there is any possibility of life and in the absence of a do not resuscitate (DNR) order, emergency workers are instructed to begin resuscitation and not end it until a patient has been brought to a hospital to be examined by a physician. This frequently leads to situation of a patient being pronounced dead on arrival (DOA). However, some states allow paramedics to pronounce death. This is usually based on specific criteria. Aside from the above mentioned, conditions include advanced measures including CPR, intubation, IV access, and administering medicines without regaining a pulse for at least 20 minutes.

In cases of electric shock, CPR for an hour or longer can allow stunned nerves to recover, allowing an apparently dead person to survive. People found unconscious under icy water may survive if their faces are kept continuously cold until they arrive at an emergency room.^[1] This "diving response", in which metabolic activity and oxygen requirements are minimal, is something humans share with cetaceans called the mammalian diving reflex.^[1]

As medical technologies advance, ideas about when death occurs may have to be re-evaluated in light of the ability to restore a person to vitality after longer periods of apparent death (as happened when CPR and defibrillation showed that cessation of heartbeat is inadequate as a decisive indicator of death). The lack of electrical brain activity may not be enough to consider someone scientifically dead. Therefore, the concept of information theoretical death has been suggested as a better means of defining when true death actually occurs, though the concept has few practical applications outside of the field of cryonics.

There have been some scientific attempts to bring dead organisms back to life, but with limited success.^[1] In science fiction scenarios where such technology is readily available, real death is distinguished from reversible death.

The Legalities of Death

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