Pro-choice philosophers have offered various laundry lists of criteria that all purport to list the properties relevant to being a person, i.e. an intrinsically valuable being worthy of moral concern and protection. One such proposal holds that the possession of a brain or brain activity is a requirement for being a person. In this post I'll briefly sketch a few problems facing this position.
There are several ways in which the brain requirement may be understood. First, we may take the brain criterion to mean that having a brain is a necessary condition for being a person. This means that although all persons must possess a brain, the mere possession of a brain is not enough to confer personhood. Second, the brain criterion may be understood to mean that the possession of a brain is a sufficient condition for being a person. This means that any being with a brain qualifies as a person simply because it possess a brain. Third, the brain criterion may state both a necessary and sufficient condition for personhood, meaning that all persons must have brains and that the possession of a brain is enough to qualify a being as a person.
Each of these interpretations faces difficulties. The claim that the possession of a brain is a necessary condition for being a person seems false; for it would appear that there could exist persons who lack a brain. There might, for all we know, exist aliens or some other species that lack brains but who are nevertheless persons capable of thinking rationally and acting freely. If this scenario is at least possible – and it certainly seems like it is – then having a brain is not necessary for being a person, for what this shows is that there is no conceptual connection between the two. The brain may enable the expression of personhood by enabling the expression of, say, the capacity to think rationally, but this function need not be accomplished only by a brain.
There is another difficulty as well, one that also applies to the claim that the possession of a brain is sufficient for personhood. Many insects and animals possess brains, but surely they aren't thereby rendered persons as well. The brain criterion will need to be modified to state that a certain type of brain is necessary or sufficient for personhood. But then what is doing the real work here is not the possession of a brain, but the possession of a brain that possesses some other morally relevant property. It is the possession of this property, not the brain, that is relevant to personhood. But possession of this property is grounded in the kind of organism that the being in question is, since the kind of organism something is serves to determine the structure of its body parts. The brain is only relevant to the expression of that property. Hence, pro-choice philosophers are sometimes accused of confusing the property of being a person with the property of functioning as a person.
So there are good reasons to doubt the adequacy of the brain criterion as relevant to personhood. Since the third interpretation of the brain criterion presupposes the truth of the first two, we may conclude that it fails as well.
Nevertheless, pro-choice philosophers might still insist that the brain surely is in some way relevant to personhood. What gives the brain criterion its intuitive force is that the brain is in a sense the “ruling part” of our bodies: it coordinates and directs the development of the whole human being. Destruction of brain function leads to the cessation of homeostasis, for the body is no longer coordinated as a single unit. This is why the criterion for physical death has traditionally been stated in terms of brain death.
But it will not work to use this as an argument against the personhood of the human embryo. Brain death is accepted as a valid criterion of death by the medical community because brain death signals the irreversible loss of human bodily functioning. When the brain dies, organs are unable to work together for the good of the whole. The various parts of the human being are no longer integrated as a single unit. The exact opposite is true in the case of the developing human. Although adult humans require a brain to integrate and direct their bodily functions, an embryo's development clearly does not require a brain to direct it. Their law-like development occurs without the direction of the brain. It is only at a later stage of development when the brain has developed sufficiently to take over the direction of bodily functioning. Hence, the parallel with brain death fails.
It seems reasonable, then, to think that the brain criterion is neither necessary nor sufficient for being a person.