Death is one of the most mysterious and inexorable problems in biology. How does life end? What is the true nature of death? Is it absolute—a fundamental state? Or is it relative and a matter of degree? Can it be defined as part of some basic reality, a detail of an unknown whole rather than merely an illusion? Although any living creature anytime can lose its life, no creature can lose its death. This is why death is safe and secure in all living things. As bioethicist Ronald Dworkin (1993) noted, death, as it were, is part of life’s dominion.
Despite the fundamental nature and importance of both the process of dying and of death itself, the concepts have received almost no attention in the basic biological sciences—textbooks seldom contain any reference to death or dying. As deaths from heart attacks decline and life expectancy rises, death has become a protracted process for more and more people (Lynn & Adamson 2003; Kass 2005). Studies on the biology of death are important because the literature that results from these studies would provide new insights into end-of-life events and processes and thus provide bioethicists, physicians and family members with a more secure biological foundation for considering ethical, legal and medical issues at the end-of-life. Understanding the biology of death will also shed light on questions concerned with time-to-death, and cause-of-death dependent patterns of death, and complex interactions among competing causes.
Death as finitude
One of the most creative thinkers in aging science was the late gerontologist George Sacher who, in a seminal but rarely cited paper (Sacher 1978), asserted that biological research on aging is the scientific response to three primitive questions. Why do we grow old? Why do we live as long as we do? Why do we die? The first question serves as the biology-of-aging field’s raison d’etre and the second question challenges life history theorists and anthropologists to explain life spans as adaptations to different environments or social situations. However, the third question that situates death in the broader context of aging science has been completely ignored. He notes that questions about death are important because, among other reasons it is the problem of transition probabilities from the stochastic changes of state from health to disease or from living to death. He believed that the problem of death must be investigated in its own right since there was no necessary relationship between aging and dying. Although he expressed concern that studying the biology of death might be intractable due to the immense variety of clinical and pathological phenomena, he none-the-less believed that (p497) “…the biology of death is in some ways more relevant to the immediate problems of human senescence than is the biology of aging or longevity.”
A preliminary model of describing the stages of death that may apply to all living organisms (with certain key assumptions) is presented in Table 1. This model describes the stages involved in what is referred to in medicine as ‘active dying’ including multiple organ systems failure. Many variations on this model can be considered. For example, the schema becomes a two-stage model for death that occurs instantaneously (severe trauma)—i.e. Stages II and III are eliminated. Patients classified as brain-dead, permanently comatose, or persistently vegetative can be considered in an arrested Stage I (descent); that is, they are in death’s grip in the sense that they can never return to the condition of their previous life. However, in both principle and in reality, they may live for decades suspended in this stage.
One of the most difficult predictions is identifying when an individual has entered into the active dying process (i.e. crossing into Stage I—irreversible descent). Although difficult, the ability to predict will never advance through physician-by-physician anecdotal observations. Systematic studies of death in model species should reveal whether it is possible a priori (as distinct from retrospectively) to identify markers indicating irreversible descent (with specified levels of probability). The general model presented in Table 1 can be further refined to include additional phases or subphases such a pre-descent stage linking death with earlier events involving aging and disablement, and a post-expiration phase linking the death of the individual as a whole with postmortem biological processes.
There are probably two main reasons why so little literature exists on the biology of death: (1) because medical research focuses on prevention and cure, death is considered the ‘enemy’ and therefore outside of the biomedical research paradigm; and (2) basic biological research has no historical precedent for studying death, not only because it represents the antithesis of life, but because a stigma may be associated with death. Developing a literature based on the systematic study of the final stages of life (the process of dying) will begin to fill in an important gap in the study of life—how life ends. In biomedical contexts, particularly with respect of ‘end of life’, research on death will help to better identify the beginning of the end more clearly. End-of-life discussions with patient and family are transitions and, thus a research model of death may provide additional, evidence, (an “earlier warning system”) for the need to make the transition and thus decisions less murky for both family and physician. The clinical definition of death is important because it defines the point at which to withdraw medical and care giving resources from decedent and, with prior consent, use the decedent as a source of organs that can be used in organ transplants. Likewise, developing a deeper understanding of dying through the use of experimental methods will be important because the knowledge will provide a more sound basis for identifying the point at which the end-phase has begun and for revealing the progressive stages in active dying that most and perhaps all living creatures experience that die naturally.
||Descent————||Through death’s portals; defined by its irreversibility in which individual is in death’s grip and cannot escape; the irreversibility is due tofailure of a one or small number of vital systems such as brain, kidney, heart, lungs.|
|II||Systems collapse||Spiraling or cascading effect of failure of all vital systems; the failure of one or a few systems in Phase I leads to cascade-like shutting down.|
|III||Mortification||Final death throes; immobilization; onset of lethargy, morbidity, and/or paralysis. This is a continuation of the collapse but here it occurs in the non-vital systems such as sensory, visual and so forth that cannot be sustained due to collapse of vital systems in Phases I and II.|
|IV||Expiration||Final release; extinction of all signs of life of individual as a whole. A few twitches so this phase too occurs over a period of time and is not instantaneous.|
Dworkin R (1993). Life’s Dominion: An Argument About Abortion, Euthanasia, and Individual Freedom. New York: Alfred A. Knopf, Inc.
Kass L (2005). Taking Care. Washington D.C.: The President’s Council on Bioethics.
Lynn J , Adamson DM (2003). White Paper: Living well at the end of life. Santa Monica.
Sacher GA (1978). Longevity and aging in vertebrate evolution. Bioscience. 28, 497-501.