Total brain death—the complete and irreversible cessation of functioning of all parts of the brain—has been widely accepted in ethics and law as a valid criterion for pronouncing the death of a human being. But in the last fifteen years, some philosophers and neurologists have advanced arguments that challenge this criterion. D. Alan Shewmon, a neurologist from UCLA, has advanced the strongest case so far. In our judgment, Shewmon has shown the unsoundness of the usual argument for the total brain death criterion, but we think—on different grounds than the standard rationale—that the criterion is a valid one for death.

The usual argument for the total brain death criterion has been that, once a human individual’s brain has developed, it is the primary integrator of all the body’s tissues and organs into a single organism. It seems to follow that, when all parts of the brain irreversibly cease to function, what remains is no longer a single organism, but an aggregate of tissues and organs.

However, Shewmon presents what appear to be counter-examples that disprove this criterion. Shewmon’s evidence seems to show that some individuals have survived total brain death. In such cases, there are many functions that seem to belong to the individual as a whole. Among these are: homeostasis of a variety of mutually interacting chemicals and physiological parameters, detoxification and recycling of cellular wastes throughout the body, maintenance of body temperature (albeit at a lower than normal level), wound healing, and, of course, respiration and nutrition (though assisted). Shewmon describes an individual called “TK” who continued to manifest all those functions for more than twenty years, even as total brain death was confirmed by repeated clinical tests.

Shewmon argues that, contrary to what has been widely assumed, the brain is not the integrator of the various systems of the body. The unity of the human organism, Shewmon argues, is an emergent property arising from the interaction among the parts of an organism. So, Shewmon argues, the total loss of functioning of the human being’s brain need not result in the loss of integration of the human organism and thus death.

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Those who suppose that brain functioning is required for the integrated functioning of the organism as a whole usually have assumed that nothing more than an aggregate of disintegrating organs and tissues survives an individual’s total brain death. We think that Shewmon has disproved that assumption by showing that TK and similar individuals are living individuals. However, it does not follow that the living individual after total brain death is the same individual who suffered brain death. Nor does it follow that the living individual after brain death is a whole human organism—that is, a rational animal. We hold that in the case of TK and others like it, what is alive after total brain death is neither the individual whose brain died nor a whole member of the human species.

Suppose a human being, John, is decapitated and that both the head and the decapitated body are kept alive (fatal bleeding is prevented, a heart-lung machine is provided for the head, ventilator support for the decapitated body, and so forth). Some have thought it obvious that the headless body would not be a human being, and that brain death is analogous to such decapitation (since in both cases the brain cannot integrate the body), and so, like the decapitated body, the brain-dead body is dead. But Shewmon correctly points out that it is only obvious that the head and the headless body could not both be identical to the human being who was decapitated. It is not obvious that the headless body would not be a human organism.

However, suppose that eventually it becomes possible to salvage everything from the waist down of youthful accident victims and to sustain that living unit for weeks pending transplantation to a suitable recipient. Suppose, too, that pending transplantation, such units manifest some internal organization—some organic unity arising from the interaction of their parts. The waist-down unit would be human in the sense that all of its cells would have the human genome, and they would constitute human tissues. But, clearly, it would not be a whole human organism; it would not be a rational animal. In fact, it would not even be an animal—that is, a sentient organism.

By contrast, if someone in an accident survived despite eventually losing everything below the heart and lungs, that individual would remain a rational animal and a human person, even though severely disabled. But the decapitated body and the totally brain-dead individual are similar to the waist-down unit rather than to the individual who has lost everything below the heart and lungs, because the headless body and the brain-dead individual are no longer sentient organisms. Neither of them is an animal, and so neither can be a human being.

The living individual after brain death (for example, the totally brain-dead TK described by Shewmon) is similar to a sustained torso and thus is not a human being. Since a human being is a rational animal, anything that entirely lacks the capacity for rational functioning is not a human being. Since rational functioning presupposes sentient functioning, anything that entirely lacks the capacity for sentient functioning also lacks the capacity for rational functioning and so is not a human being. Since the human being is a mammal, a brain, or the capacity to develop a brain, is necessary for its capacity for sentient functioning. (We refer to mammals because some animals are sentient without a brain, but the brain plainly is necessary for mammals’ sentience.) Therefore, any entity that entirely lacks a brain and the capacity to develop a brain is not a human being. That brief argument may be clarified by the following considerations.

In daily life we recognize beings of distinct types, centers of specific types of actions and reactions, and we treat each type of being according to its nature. Thus, we deal with a lion and a lamb differently, because they have distinct tendencies to act and distinct ways of reacting—different natures. An individual with a particular nature is a stable entity with an inherent tendency, or unified set of tendencies, to act and react in certain ways.

Bodily living things (organisms) have capacities—tendencies to grow, nourish themselves, adapt to environmental conditions, maintain inner balance, and reproduce. A living thing can possess a capacity and yet be impeded, by external or internal factors, from exercising it. For instance, even a mammal with good eyesight cannot see in pitch darkness (an external blockage), and an anesthetized patient cannot feel pain (an internal blockage).

Moreover, a living being has a radical capacity for a function if it has within itself a material constitution that disposes it, given a suitable environment, to develop sufficiently to perform that function. Cuttings from many species of plants, although without an immediately exercisable capacity to reproduce, have the internal resources to develop themselves to the stage at which they will have all the exercisable capacities of a complete plant of their species, including the capacity to reproduce. Thus, natural kinds are defined not only by their first-order capacities, but also by their second-order capacities—radical capacities to develop first-order ones.

A human being is a rational animal. An animal is a sentient organism. In human beings and other mammals, sentience includes such functions as seeing, hearing, feeling pain and pressure, perceiving, desiring, fearing, being angry, and so forth. Embryonic mammals do not actually perform such actions but they have within themselves the resources to develop themselves so that they do have the capacity, and so are sentient organisms.

The rationality that differentiates human beings from other animals includes such functions as conceptual thought, reasoning, and making deliberate choices. An organism that has the capacity for these types of actions is a human individual.

Human embryos and fetuses are human organisms because they too have the internal resources to develop themselves to the stage where they will be able to perform the actions characteristic of the human kind (for support of this point, see Chapter 4 of Body-Self Dualism in Contemporary Ethics and Politics by Patrick Lee and Robert P. George). By contrast, even when the cells in teratomas or complete hydatidiform moles have the human genome, such disorganized growths are not human beings since they lack both first- and second-order capacities for specifically human functions.

Conceptual thought, reasoning, and deliberate choices are not directly observable. So, human individuals can perform such actions without providing evidence that they are doing so. However, to be a rational animal, an organism must be an animal; and to be an organism of that kind, it must have either the capacity for sentience, or the capacity to develop the capacity for sentience. Moreover, because the conceptual thought, reasoning, and deliberate choices of rational animals bear upon experienced things, those rational functions presuppose sensory functioning. Therefore, if an organism lacks the capacities for sentient functioning and the capacity to develop those capacities, it cannot be an animal (a sentient organism); and if an organism entirely lacks capacities for sentient functioning and is not an animal, it cannot engage in conceptual thought, reasoning, or deliberate choices, and is not a rational animal.

There also is common agreement that no mammal can sense without brain functioning—a mammal’s sentience requires either a brain capable of functioning or the capacity to develop a brain. But a totally brain-dead individual neither has a brain capable of functioning nor the capacity to develop a brain. It follows that any mammalian individual that undergoes brain death is no longer a sentient being, and thus not an animal. An individual such as TK, therefore, that has undergone total brain death, is not an animal and so not a rational animal, a human being.

One might object that a totally brain-dead organism might have a radical or second-order capacity for brain functioning inasmuch as it still has the genetic-epigenetic constitution that oriented it toward the development of a functioning brain. However, the appropriate genetic-epigenetic constitution within the cells of a multicellular organism is not a sufficient condition for a second-order capacity for brain functioning. The developing cells also must be of certain types or structures, and those cells must be arranged in a certain way if the organism is to develop a functioning brain. So, while a human embryo has a second-order capacity for brain functioning, a totally brain-dead organism has no such capacity.

It might also be objected that the argument for the total brain death criterion implies that all of those who are in permanent comas, or even many in persistent vegetative states, are dead, and that is false, since such people are still warm and pink, and may be breathing on their own. However, our position that the irreversible loss of specifically human capacities is the human being’s passing away does not entail that everyone who is unconscious and will never regain consciousness is already dead. Many unconscious people who will never regain consciousness would regain it if they were given appropriate care. Our position only entails that the loss of the capacity for consciousness is death.

We think it is beyond reasonable doubt that brain-dead entities entirely lack the capacity for the sentient functioning that is presupposed by human consciousness; but it is not beyond reasonable doubt that individuals who are warm and pink and breathing but not totally brain-dead lack that capacity. Reasonable doubts follow from several considerations.

To start, patients confidently judged to be unconscious after careful and repeated examinations sometimes later recall undergoing those examinations. The immediately exercisable capacity to respond to stimuli is one thing; consciousness is another. Then too, patients confidently judged to be permanently comatose or in a permanently vegetative state sometimes recover, and attempts to treat such patients have recently met with some success. Pathological unconsciousness is one thing; the loss of the capacity for consciousness is another. Thus, the fact that a patient has lost the capacity for consciousness is extremely difficult to establish beyond reasonable doubt.

Some argue that the capacity for consciousness can be lost without total brain death, and conclude that it is too stringent a criterion for death. But such arguments depend on identifying parts of the brain required for sentient functioning, and several recent studies have made it clear that such identifications are problematic. Moreover, this essay has been concerned exclusively with the adequacy of total brain death as a conceptual criterion for the death of a human individual. We have not addressed the adequacy of current clinical tests to establish beyond reasonable doubt that total brain death has occurred. But when it has occurred, a human organism has died.