It is well known that the cells used to generate embryonic stem cell lines are drawn from a late-stage blastocyst, a five–six-day-old human embryo, and that this process typically results in the destruction of the blastocyst. Those who claim strong moral standing for the early human embryo regard this means of generating stem cell lines as the murder of innocent human beings. Moral theorists who endorse embryonic stem cell research marshal a variety of arguments to refute the claim that the early human embryo has strong moral standing. Many of these authors appeal to the ambiguous nature of the early human embryo; they argue that because the early human embryo is subject to both twinning (embryo-splitting) and fusion (separate embryos combining to form a single embryo) it is not even a distinct individual. These authors maintain that because the human embryo can twin or fuse until roughly the fourteen-day mark – the point at which specialized cell differentiation and the formation of the primitive streak begin – the human embryo has no moral standing at all prior to fourteen days.Footnote 1
I argue that appeals to twinning and fusion cannot demonstrate that the early human embryo lacks strong moral standing. I recognize one possible exception here, a particular version of the appeal to fusion that will be discussed at the end of this article.
Section I surveys the other arguments against the moral standing of the early human embryo. Section II explains twinning and fusion, as well as the most straightforward appeals to twinning and fusion. Here, I argue that simple arguments from twinning and fusion carry absurd implications about the moral standing of other entities.
Section III considers a reformulation of the twinning argument that pays closer attention to the way in which human embryos twin and fuse. According to this version, while some entities that twin may be distinct individuals prior to twinning, the human embryo can twin precisely because it is already multiple and indistinct. I argue that these appeals exaggerate the moral relevance of the early human embryo's supposed multiplicity.
Section IV deals with arguments based on intuitive reactions to embryo twinning and fusion. One might argue that the moral standing of the early human embryo is inconsistent with the fact that we do not react to twinning and fusion in the way that we react to the deaths of adults or children. I use an appeal to Derek Parfit's treatment of personal identity to block this version of the twinning/fusion argument, but I concede that one version of the fusion argument may succeed in this context.
In using the term ‘early human embryo’ I refer to the first fourteen days of the embryo's life, up to the point where significant cell differentiation and the development of the primitive streak begin. I shall use EHE as a short form for the term ‘early human embryo’ and MSEHE as a short form for the position that the early human embryo holds strong moral standing comparable to that of a developmentally normal human child or adult.Footnote 2
I. THE OTHER ARGUMENTS
I shall attempt to capture these arguments in three broad categories: (1) appeals to natural properties arguments; (2) logical problems of appeals to potential arguments; and (3) counter-intuitive implications arguments. A brief survey of these arguments will help to determine whether twinning and fusion add anything to the existing arsenal of arguments against MSEHE.
A. Appeals to natural properties arguments
MSEHE opponents regard the developmentally normal adult human being as the paradigmatic example of strong moral standing. They argue that the extension of similar moral standing to other entities, including children, depends on identifying the morally relevant natural property (or properties) that ground(s) the paradigm example's moral standing.Footnote 3 Some authors have identified the level of rationality typical of adults as the natural property that is crucial to the acquisition of strong moral standing.Footnote 4 However, prioritizing rationality in this way may diminish or even eliminate the moral standing of young children. And very few of us regard this implication as remotely plausible. For this reason, other authors have treated sentience – the capacity for pain and pleasure – as sufficient to ground some level of moral standing.Footnote 5
To some, this seems unfair. The embryo and the fetus, even if they currently lack sentience, are identifiably human and developing towards sentience. This response, however, meets with a familiar objection.
B. Logical problems of appeals to potential arguments
If it is the possession of a property, X, that confers moral standing, then the mere fact that an individual has the potential to acquire X does not by itself confer moral standing on that individual. Potential persons are potential persons, not persons.
Attempts have been made to circumvent the logical problems of appeals to potential, most notably Don Marquis's pro-life deprivation of a future-like-ours argument.Footnote 6 Marquis seeks to avoid the question of whether the embryo or fetus is a person; instead, he focuses on the question of what it is that makes killing an adult or a child a serious moral wrong. Marquis concludes that it is the deprivation of a valuable future (a future-like-ours) that makes such a killing a serious moral wrong. Since the killing of a fetus or embryo deprives such entities of a future-like-ours, such killings are comparable to murder.
In his well-known abortion paper, Marquis maintains that his argument does not entail that birth control is a serious moral wrong. In his view, prior to fertilization, there is no distinct entity with a future-like-ours. Rather, there are merely various possible combinations of sperm and ova. No individual sperm or ovum can claim to have such a future, and no merely possible combination of sperm and ovum can lay such a claim either.Footnote 7 Moreover, as we shall see in section III, Marquis now argues that even the fertilized EHE is not the kind of distinct individual that can be deprived of a human future.Footnote 8
The future-like-ours argument has been widely criticized. Many authors have argued that in order to have a morally relevant claim to a future, an individual must already possess moral standing.Footnote 9 If it does not, then it is not wronged by the loss of its future, even if that future would have been like ours.Footnote 10
However, MSEHE proponents may seek to avoid the logical problem of potential by treating the intrinsic drive towards full human development as an actual property that is sufficient for moral standing. Consider John Finnis's account of MSEHE.
People might say that the early human embryo is not a human subject, because it is very small. And indeed it is . . . by every standard of reasonable judgement the fact that you in the first days of your life, and I in the first days of mine, were very small has no tendency at all to show that that very embryo which you were was not you, or that that very embryo, that small embryo, was not me. Each of us was even then and there equipped with our genetic constitution – do not say genetic blueprint, because we were and are three-dimensional, not two-dimensional – the whole genetic constitution which made you you and me, for better or worse, me . . .
The criterion is whether the new cell has the genetic primordia for self-directing development into a mature individual of an animal species . . . Footnote 11
For Finnis, I am identical with the EHE that grew into me. In referring to it we simply point to me at an earlier stage of my development in the same way that referring to my infancy points to an earlier stage in my development. So, on Finnis's terms, it seems absurd to say that the embryo could be me, but that it, unlike the me of today, lacked moral standing.Footnote 12
By itself, this is unconvincing. That I am, in some sense, the same individual as my EHE does not imply that it had moral standing. There is some sense in which I am the same individual as my future corpse. However, it does not follow that my corpse has moral standing. Of course, many us of would say of a loved one's dead body or living but brain-dead body, ‘That is no longer her’. We say this because what was important to us about that individual has ceased to exist, yet there is still some sense in which that body is, or is what is left of, that person. What remains lacks moral standing. Similarly, I might refer to my EHE as me before I obtained moral standing, or I might refer to it as the thing that built itself – with no small amount of help from my mother – into me.
In accusing MSEHE opponents of inconsistency, Finnis simply conflates different uses of the term ‘identity’. In my view, I have moral standing because I am sentient. My earlier self lacked moral standing because it had only the potential for sentience. In the most important sense, it was not yet me. You may disagree with this view, but it is not self-contradictory.
Perhaps, however, Finnis's MSEHE can be presented as logically consistent – if he refrains from accusing his opponents of such inconsistency. In essence, Finnis thinks that the EHE has moral standing because it is not merely a blueprint for a human being. It is a living three-dimensional entity that is already biologically human and is engaged in the internally directed process of building itself into the adult human organism detailed in its self-contained blueprint. For Finnis, human entities with totipotency and inner-directedness command respect. Likewise, because every person's EHE contained the blueprint for her construction, Finnis thinks that we should recognize a morally crucial sense of connection with our EHEs. I see no logical error in committing oneself to this position. However, one can, without inconsistency, deny the moral relevance of both the EHE's inner-directedness and its connection to possible future persons.
C. Counter-intuitive implications arguments
MSEHE proponents can designate totipotency and inner-directedness as natural properties that together confer strong moral standing on the EHE. This may allow them to escape complaints about the conflation of actual and potential capacities. However, even if we accept this, another set of arguments against MSEHE remains. I call these the counter-intuitive implications arguments.
Authors such as Ronald Green have argued that the totipotency and inner-directedness criteria cannot be restricted to EHEs and fetuses. As Green argues, the question of which entities possess the genetic primordia for development into complete human organisms is closely tied to questions about our current technological abilities. The EHE cannot develop into a complete adult human organism without a great deal of help – help that we can currently provide. But all the cells in our body have some potential for such development, though we currently lack the technology to assist them in this regard. With further technological development, the list of cells with the relevant genetic primordia might be expanded to the point where our interests would have to be weighed against the developmental interests of our various bodily cells.Footnote 13
In response, MSEHE proponents are likely to emphasize the inner-directedness of the human embryo, making use of their own argument concerning the logical problem of appeals to potential. One may argue that the EHE already possesses the requisite inner-directedness towards full human development, while somatic cells would have to be manipulated to take on this capacity. However, recent evidence indicates that this argument underestimates the role of an embryo's environmental conditions in the stimulation of cellular development. These findings threaten to undermine the distinction between the inner-directedness of the EHE and the ‘mere’ developmental potential of somatic cells.Footnote 14
Moreover, MSEHE proponents may not grasp the practical implications of according strong moral standing to EHEs. If EHEs have strong moral standing, then we should recognize not just their right not to be killed, but also their positive claims to assistance. We struggle to cure not just man-made diseases, but natural illnesses and deaths. Many early pregnancies terminate spontaneously, some estimates putting the count at roughly five embryo deaths for every live birth.Footnote 15 As Green and other authors have asked, if EHEs have strong moral standing, why have we not seen a call for a war on natural embryo death similar to the wars declared on diseases such as cancer? The absence of such calls indicates that proponents of MSEHE are not consistent in the application of their own position.Footnote 16
I shall not pursue the question of whether MSEHE proponents can provide successful responses to these arguments. However, comparisons with these arguments will help us to assess the independent merits of the arguments from twinning and fusion.
II. TWINNING AND FUSION
Identical (or monozygotic) twins occur in nature from embryo-splitting during the early stage of pregnancy. Moreover, this process can be replicated in the laboratory on embryos fertilized in vitro. Such embryos can be implanted for the purpose of attempting reproduction, but they can also be used for research purposes. Since twinned embryos are essentially perfect clones of each other, they have great potential in research as they can provide a series of qualitatively identical test subjects.Footnote 17
Embryo-splitting remains possible until roughly the fourteen-day mark, when significant cell differentiation and the formation of the primitive streak (the precursor of the spinal cord) begin. At the four-cell stage of embryo development, each individual cell remains totipotent; each has the capacity, if separated from the others, to develop naturally into a complete adult human organism. After this stage, individual cells begin to lose their totipotency, but the precise point at which individual cells cease to be totipotent is difficult to determine. Past the eight–sixteen-cell stage, embryo-splitting is still possible, but this splitting is a matter of groups of cells breaking off from the originator. The resulting collections of cells may form new embryos that retain totipotency, though, under natural conditions, the individual cells within these new embryos are no longer totipotent by themselves.Footnote 18
Split embryos can recombine to form a single embryo that is genetically identical to its multiple predecessors and to their originating embryo. On the other hand, ‘so-called tetragametic chimerism . . . occurs through the fertilization of two ova by two spermatozoa, followed by the fusion of the zygotes and the development of an organism with intermingled cell lines’.Footnote 19 The person that results from the new combined embryo will be a genetic hybrid. His body will be composed of tissues from both cell-lines. In the event that two separately fertilized male and female embryos fuse, the resulting human chimera may develop as a hermaphrodite.Footnote 20
Perhaps the best-known twinning argument comes from Helga Kuhse and Peter Singer. Kuhse and Singer argue that the occurrence of twinning leaves us with no plausible explanation regarding the fate of the human individual that produces a new twin pair of human embryos. Consider a new EHE, Tom. At the eight-cell stage Tom splits into two separate but otherwise identical cell groups that go on to be born as monozygotic human twins. We cannot say that Tom continues to exist as one or both of the resulting twins. There is no reason to privilege one over the other as Tom's successor, and they cannot both be Tom as they are not numerically identical with each other. Yet it also seems implausible to claim that Tom has died or ceased to exist, as this ‘will put one in the difficult position . . . of having to explain how it can be that a human individual has ceased to exist when nothing has been lost or has perished – in other words, when there has been a death but there is no corpse’.Footnote 21 For Kuhse and Singer, the solution to this difficulty is to accept that Tom never was a human individual with moral standing; Tom the EHE was merely a collection of cells.
Fusion offers a similar puzzle. When twinned embryos recombine, we are left with one rather than two. Again, there is no corpse. Nothing seems to have died. Similar considerations apply to the fusion of separately fertilized ova; no cell dies, though, as the result of this fusion, neither of the genetic plans from the preceding embryos will achieve full expression in an adult human organism.
Following Singer, authors such as Katrien Devolder, John Harris, and Green take it as intuitive that twinning renders the embryo too ambiguous to hold moral standing. According to Devolder and Harris, the EHE ‘is a deeply, perhaps irretrievably ambiguous entity, one that defies classification and slips seamlessly between moral and biological categories’.Footnote 22 Supposedly, the embryo's plasticity entails that it is not a distinct individual, so the question of whether it is has morally relevant natural properties doesn't get off the ground.
Finnis's response is a terse ‘But so what?’.Footnote 23 His intuitions regarding the simple possibility of twinning are shared by some of the authors who reject MSEHE. According to Jeff McMahan, ‘[t]hat an entity can undergo division is no reason to think it is not a unique individual. It is no reason to think that an ameba is not an individual ameba, that it can divide, or that any other cell is not a unique individual object because it can undergo fission.’Footnote 24
Here it is important to draw a distinction between the mere occurrence of twinning and the explanation of how a particular form of life twins. For McMahan, the simple fact that an entity can twin is of no moral significance; it certainly doesn't show that the predecessor of two twins was not, during its life, a distinct individual. However, for McMahan, the particular way in which EHEs twin reveals that they are not distinct individuals. I take up McMahan's argument on this issue in section III. For now I will focus on the moral relevance of the mere occurrence of twinning and fusion. Call this the simple twinning/fusion argument.Footnote 25
The simple twinning/fusion argument holds that MSEHE fails just because EHEs can twin or fuse. But the proponent of MSEHE should not concede this unless his antagonist concedes that the threat posed by twinning/fusion is symmetrical; the antagonist should concede that the possibility of twinning or fusion would negate the moral standing of entities that otherwise satisfy his own criteria for moral standing. He should accept that twinning or fusion would negate the moral standing of any entity that might otherwise hold moral standing. If sentient beings, for instance, are preserved against the argument, then the simple twinning/fusion argument is parasitic on appeals to sentience as the natural property that determines moral standing.
A. Twinning persons by technology
Of course, no known sentient beings are capable of twinning or fusion, but such beings are possible, at least in principle. Here, David Oderberg appeals to split-brain thought experiments to contest the soundness of arguments from twinning.Footnote 26 Consider Parfit's description of these cases.
My Division. My body is fatally injured, as are the brains of my two brothers [we are identical triplets]. My brain is divided, and each half is successfully transplanted into the body of one of my brothers. Each of the resulting people believes that he is me, seems to remember living my life, has my character, and is in every other way psychologically continuous with me. And he has a body that is very like mine.Footnote 27
Parfit invokes the possibility that each half of the brain could retain both one's memories and personality, as well as a continuing conscious life of its own.Footnote 28 We might also imagine that new bodies are made available not by the brain death of one's brothers, but by genetically engineered backups, cloned for just such an occasion. Here, we have a tight analogy with embryo-splitting.
We can tell a similar story about fusion. Suppose that we could surgically fuse two halves of two different brains together in the body of one of the two ‘donors’. Here we lack even the weak evidence concerning separate centers of consciousness in brains that have been split (had their corpus callosum severed), so the idea that such a surgery might produce a hybrid individual with a combination of memories and personality traits from each ‘donor’ is even more the stuff of wild science fiction. But again, it is possible in principle.
According to Oderberg, we may regard the brain-splitting surgery as the death of the original subject (I shall contest this in section IV), so there is no post-fission individual that is numerically identical with the pre-fission individual.Footnote 29 However, it does not follow that the pre-fission individual was not an individual with a distinct identity of his own. That identity does not continue does not imply that there never was a distinct individual in the first place.
We would not deny the moral standing of sentient human beings if twinning technology became available. How then can the opponent of MSEHE expect his interlocutor to accept the supposed force of the simple twinning/fusion argument? This splitting results in two new individuals that are qualitatively identical to their predecessor, two new individuals that bear the crucial property of sentience. When a human embryo twins, two new individuals that are qualitatively identical to their predecessor emerge, two new individuals that have totipotence and inner-directedness.
The same analogy applies to fusion. In the case of sentient beings, we go from two distinct sentient beings to one sentient being that is an amalgam of its predecessors with respect to personality and memory. The resulting one person is still a sentient being. In the case of separately fertilized embryos, we go from two distinct embryos to one embryo that will work from a combination of the two genetic codes provided by its predecessors; the new single embryo will still be totipotent and inner-directed in character. In the case of previously twinned embryos that fuse, we go from two embryos with identical genomes to one embryo that holds this genome. In each case, the single entity that emerges still satisfies MSEHE's criteria for moral standing.
Again, it will do no good to complain that the human embryo is not sentient. If that is a decisive consideration here, then it is the appeal to sentience, not the simple twinning/fusion argument that does the real work.
Opponents of MSEHE might argue that the simple twinning/fusion argument should not be applied to sentient beings. Surely everyone, including proponents of MSEHE, admit that sentience is a sufficient, if not a necessary, condition of moral standing. So opponents of MSEHE might claim that all parties should agree that sentient beings are immune to the otherwise decisive force of the simple twinning/fusion argument; this would avoid the absurd result of denying the moral standing of sentient beings. But proponents of MSEHE can avoid this absurd result by rejecting the simple twinning/fusion argument altogether, and there is no reason for them to accept a version of the argument that is tailored against MSEHE.
B. Natural twinning of persons
Opponents of MSEHE might argue that there is an important difference between the natural twinning of the EHE and the artificial twinning of human persons. EHEs, they might say, are ambiguous non-individuals because they twin in nature, while human persons are genuine individuals because their twinning would not result without artificial human interference.
This places too much weight on the so-called ‘natural course of events’, and MSEHE opponents have contested such weighting in their own arguments. Recall that proponents of MSEHE attempt to block the extension of the totipotence and inner-directedness criteria to somatic cells and stem cells by arguing that these cells cannot develop into full human organisms under natural conditions. According to Green, this overstates the importance of the natural course of events, since there are a wide variety of circumstances under which we struggle to protect people from the effects of nature (aging, diseases, etc.). So Green rejects the argument that appeals to the natural course of events can be used to disqualify one of two otherwise satisfactory candidates for moral standing.Footnote 30 However, it may seem that MSEHE proponents who use appeals to the natural course of events are vulnerable to a version of the simple twinning/fusion argument that uses the same distinction to privilege sentient beings.
This advantage for the opponents of MSEHE is easily negated. Imagine a race of sentient intelligent creatures who occasionally twin, generating two successors that are both qualitatively identical to their originator.Footnote 31 Sometimes these creatures fall to the ground and find themselves immersed in a cocoon. While in the cocoon, an individual breaks into two halves with each half holding the ability to re-grow its missing brain tissue and bodily material. Assume, if you like, that the creatures have a redundant memory storage capacity that allows both new individuals to emerge with all the memories and personality traits of the original. We can tell a similar story about small groups of these creatures occasionally finding themselves drawn together, forming a cocoon from which emerges a single individual, a hybrid of the cocooned individuals.Footnote 32 I doubt that many persons would think it permissible to kill such creatures merely because there is some possibility, or even a certainty, that they would twin or fuse. If they are intelligent and sentient, then they have strong moral standing; their tendency to twin or fuse is irrelevant.
C. Possibility and certainty
We would not apply the simple twinning/fusion argument to sentient beings. Therefore, we cannot expect proponents of MSEHE to accept the application of this argument to the EHE. One caveat before we move on to section III. Oderberg claims, rightly I think, that the question of whether twinning is a mere possibility, as opposed to a certainty, is, for the most part, irrelevant.Footnote 33 Even if we knew that a person was certain to undergo fission five minutes from now, he would still be a person with a right not to be killed. Yet for many of us, the fact that a person will certainly die in short order seriously diminishes the wrongfulness of killing that person, especially if doing so would achieve some worthwhile goal or end. Consider the case of killing one person who blocks our exit from a cave in which we will drown because of fast-rising water. This person is stuck facing into the cave and he will die with us in mere minutes if we do not kill him now in order to remove him (double-effect does some but not all of the work here).Footnote 34
Similarly, if we did know that embryos were going to twin within mere moments, might it not be permissible to kill them now in order to use them for valuable projects?Footnote 35 I doubt that many proponents of MSEHE would accept the extension of this intuition to cases of twinning and fusion. Likewise, I do not think that the wrongness of killing a person would be significantly diminished if we knew he was about to twin or fuse. I will return to this issue in section IV.
III. HUMAN EMBRYO TWINNING IN CONTEXT
As I noted in section I, McMahan rejects the simple twinning/fusion argument, but he does think that reflecting upon human embryo-splitting shows MSEHE to be false. On McMahan's view, while the amoeba is a single distinct individual prior to its twinning, the human embryo is multiple and ambiguous before – and regardless of whether – twinning actually occurs.
According to McMahan,
[I]t is unclear what makes all the various cells, considered synchronically or diachronically, parts of a single individual. They are all contiguous within a single extracellular membrane (the zona pellucida), but that alone does not make them a single entity any more than placing a number of marbles in a sack turns them into a single entity.Footnote 36
Marquis follows a similar line of reasoning in attempting to block the application of his anti-abortion argument to the EHE. He argues that the multiplicity of the EHE precludes the idea that the EHE is an individual that can be deprived of a future-like-ours. Consider the four-cell-stage embryo. At this stage, there are four qualitatively identical totipotent cells within the zona pellucida; they cannot all be the individual that holds a future-like-ours. Nor is there any reason for saying that any one of them is that individual. Any such selection would be arbitrary. Nor can we say, according to Marquis, that the four cells held within the zona pellucida form a single larger moral individual.Footnote 37
‘Imagine’, asks Marquis,
a number of human beings at a cocktail party held in one room. It is hard to believe that the fact that those human beings are surrounded by the walls of the room shows that the cocktail party itself is some super human being over and above the human beings at that cocktail party . . . even if the zona pellucida makes the embryo an individual, it does not make the embryo the right kind of individual to have a future of value and, therefore, the right kind of individual such that it would be wrong to destroy it.Footnote 38
Marquis does concede that the zona pellucida is not merely a set of walls. He recognizes that ‘nutrients flow from outside to inside the zona pellucida and also within different cells inside the zona pellucida’.Footnote 39 However, Marquis dismisses this simply by noting that, if hors d'oeuvres pass in, out of and around a cocktail party, this does not make that cocktail party some kind of superhuman individual.
Marquis's analogy understates the level of interaction and differentiation between the cells of the EHE. As Robert P. George and Gómez-Lobo note, ‘[m]onozygotic twinning usually occurs at the blastocyst stage, in which there clearly is a differentiation of the inner cell mass and the trophoblast that surrounds it’.Footnote 40 Moreover, even prior to fertilization, the ovum has an ‘animal’ pole and a ‘vegetable’ pole. At the two-cell stage after fertilization, the cell coming from the ‘animal’ pole is likely to form the basis of the nervous system while the cell extending from the ‘vegetable’ pole is likely to generate the precursor of the lower organs. So it is not clear that the EHE is merely a collection of totipotent cells.Footnote 41
However, according to George and Gómez-Lobo,
the clearest evidence that the embryo in the first two weeks is not a mere mass of cells but is a unitary organism is this: if the individual cells within the embryo before twinning were each independent of the others, there would be no reason why each would not regularly develop on its own. Instead, these allegedly independent, noncommunicating cells regularly function together to develop into a single, more mature member of the human species. This fact shows that interaction is taking place between the cells from the very beginning (even within the zona pellucida, before implantation), restraining them from individually developing as whole organisms and directing each of them to function as a relevant part of a single, whole organism continuous with the zygote. Thus, prior to an extrinsic division of the cells of the embryo, these cells together do constitute a single organism. So, the fact of twinning does not show that the embryo is a mere incidental mass of cells. Rather, the evidence clearly indicates that the human embryo, from the zygote stage forward, is a unitary, human organism.Footnote 42
For his part, McMahan recognizes that the EHE may display more coordination than he was willing to admit in his earlier writings. However, he points out that the ‘question of when the level of differentiation and coordination becomes sufficient for the presence of a human organism is not a biological or scientific question but a metaphysical question. How we ought to answer it is a matter of overall coherence among our beliefs and concepts.’Footnote 43
Here McMahan argues that our judgements concerning the beginning of life for human organisms should cohere with our intuitions about their ends. In his view, accepting the minimal coordination present in the EHE as sufficient for moral standing would make it difficult to retain the concept of brain death. For ‘brain death is compatible with residual functioning among cells, tissues, and even organs that is far more extensive and highly coordinated than that found among the cells in a two-day-old or six-day-old embryo’.Footnote 44 So it would appear that if we are committed to recognizing the moral standing of an EHE as a human organism, we are also committed to the moral standing of some of the brain-dead.
But this is not the case. McMahan seems to think that the proponent of MSEHE is committed to the idea that just because the EHE satisfies a certain minimum level of cellular coordination and integration, the EHE has moral standing. If this were the case, then MSEHE would entail the moral standing of some brain-dead persons: those who satisfy a higher degree of cellular coordination than the EHE. A seemingly absurd result.
However, proponents of MSEHE need not claim that there is some threshold of cellular coordination such that human life that satisfies this threshold holds moral standing. The issue of coordination arises because the opponent of MSEHE alleges that the EHE is not coordinated enough to constitute a distinct living individual. According to opponents of MSEHE such as McMahan, because the EHE is not a distinct individual, the question of whether the EHE bears the right kind of natural property doesn't get off the ground. In other words, this dispute is about whether the proponent of MSEHE can satisfy a necessary condition of moral standing – showing that the EHE is a distinct living individual. In showing this, the proponent of EHE does not have to commit himself to the idea that all living human individuals have moral standing.
The proponent of MSEHE maintains that the EHE displays a level of coordination and integration such that we can describe it as a single totipotent entity with an inner-directedness towards development into a complete human organism. In other words, it is a living human individual with natural properties that ground strong moral standing. Cells and organs within a brain-dead human body may display more complex coordination and integration than that found in an EHE. Perhaps, then, the brain-dead body is a living human individual. But a brain-dead human no longer has the capacity for sentience or the kind of cellular activity that is building towards sentience, so MSEHE does not imply that the brain-dead have moral standing.
The EHE is a single living organism. The question is whether it bears a natural property that grounds moral standing. Totipotency and inner-directedness may not be such properties, but appeals to the embryo's multiplicity do not establish this conclusion.
IV. OUR REACTIONS TO TWINNING AND FUSION
The final version of the twinning/fusion argument concerns our reaction to twinning and fusion. As McMahan says,
There are some who hold that abortion is wrong on the basis of two claims: first, that we begin to exist at conception and, second, that it is a terrible loss when one of us dies, even in utero. Those who hold this view seem to be committed to the conclusion that monozygotic twinning is bad, as it involves the ceasing to exist of one of us. Admittedly, the one who ceases to exist makes way for the two who come to exist; but the phenomenon should still be seen, on this view, as tragic overall.Footnote 45
This, of course, assumes that twinning does constitute, in an important sense, the end of the pre-twinned individual. Oderberg accepts this much, but he maintains that while there are good reasons for limitations on our regret, twinning does in fact call for a kind of mourning. However, he does not claim that diminished regret concerning twinning is explained by the fact that twinning is natural; he notes that we often experience a great sense of tragedy concerning natural deaths. According to Oderberg, we need not mourn the twinning of an embryo the way we mourn the death of a child, but this is, in part, explained by the fact that no one ever developed a social relationship with the pre-twinned embryo. Likewise, no one finds out about the death of the pre-twinned embryo until well after the fact. These factors justify limitations on our feelings of regret; however, a full appreciation of twinning does call for us to mourn the death of the original embryo in something like the way that we mourn the deaths of strangers.Footnote 46
Like McMahan, I find this response quite bizarre. Twinning is infrequent, but other spontaneous deaths of EHEs are not. As McMahan notes, Oderberg and other proponents of MSEHE have much mourning to do.Footnote 47 More importantly, as Green points out, the deaths of these tiny persons appear to call out for action. Why do the proponents of MSEHE not call for a research agenda dedicated to protecting tiny persons from destruction by embryo-splitting and fusion?
But MSEHE proponents need not follow Oderberg here. Instead, they should contest the idea that twinning is, in any simple way, the end of the EHE's existence. Opponents of MSEHE emphasize the logical point that the embryo cannot continue to exist as one or both of its twins, since these entities cannot be both identical with the predecessor and non-identical with each other. They are not identical with each other, so they cannot be identical with the predecessor. As Elizabeth Harman suggests in a recent paper, this appeal to the strict sense of identity invites an appeal to Parfit's discussion of identity and survival.Footnote 48 However, I think that Harman's particular view of how Parfit's discussion of identity applies to the twinning/fusion issue is mistaken. Please refer to the Appendix for an explanation of my disagreement with Harman.
A. Reactions to twinning
Consider again Parfit's split-brain surgery thought-experiments. Assume that the resulting individuals each share half of my brain (and if you like a cloned body genetically identical to my original one). Each resulting individual begins its new life with all the memories and personality traits that I held just prior to surgery. Does my identity continue after the surgery? Presumably, MSEHE opponents say ‘No’ just as they deny that twinned embryos can be identical to their predecessor (they are not identical with each other). Parfit agrees of course, but the lesson he draws from this is that identity is not what is most important in survival.Footnote 49
According to Parfit's reductionist view, the key to continuing personal identity and survival is psychological continuity. As long as one and only one being that is psychologically continuous with me carries forward into the future I both survive and my identity continues. Here Parfit thinks that we should rely solely on psychological continuity, abandoning any great concern with physical continuity. Hence, if I am ripped apart by a machine that reads me and copies all data on my brain and body and then perfectly reconstructed out of entirely new physical material at a different location, I continue to exist.Footnote 50 Now one may be sympathetic to Parfit's view while still thinking that survival and identity require some physical continuity, at least with respect to the continuation of the brain. Of course, Parfit has additional thought-experiments that are intended to disabuse us of this commitment to physical continuity, but I shall not pursue these here (in the story I will tell about the human embryo, there is something to satisfy those who remain concerned with physical continuity).Footnote 51
As Parfit says,
I would survive if my brain was successfully transplanted. And people have in fact survived with half their brains destroyed. Given these facts, it seems clear that I would survive if half my brain was successfully transplanted, and the other half was destroyed. So how could I fail to survive if the other half was also successfully transplanted? How could a double success be a failure?Footnote 52
As Parfit points out, nothing is missing in my relation to either of my successors. Each has what it takes to be me. That there are two of them rather than one does nothing to undermine what is important about the connection I have with each of them considered individually (this holds true even for someone who still wishes to retain a commitment to the importance of physical continuity, since both have half of my brain). Division seems, at least prima facie, to be about as good as, if not better than, ordinary survival.Footnote 53
Of course, there would be practical complications. My property rights and social obligations would have to be divided amongst my new ‘heirs’. Likewise, there would be difficult questions about the relationship of my ‘heirs’ to my spouse, children and closest friends. In a society of intelligent sentient beings that occasionally twin, the relevant social institutions and related moral concepts would need to be adjusted to accommodate the occurrence of division. But, as I shall argue, none of these complications applies to the human embryo, which has yet to take on any moral and social baggage of its own.
Proponents of MSEHE hold that totipotence and inner-directedness are sufficient to confer strong moral standing on the EHE. It makes sense for them to treat the preservation of the genetic plan provided by an embryo as the analog of psychological continuity in Parfit's account of survival and personal identity. For already sentient beings, what matters is that a sentient being that is psychologically (and perhaps physically) continuous with them carries on. What matters to the continuation of the EHE is that its project of building a complete human being according to the specifications of its genetic map continues. If this project continues on a one-to-one basis, the embryo survives in the ordinary sense. If this project continues in two or more new individuals as the result of embryo-splitting, we have the kind of survival that I could have through brain division.
Note that a perfect analogy with Parfit's reasoning would have MSEHE proponents accept the following: if the embryo were to be read and disassembled, its identity would continue if we, using the data from the reading, constructed a perfect copy of it from other material. Moreover, if we built two such copies, the embryo would survive in the same sense that it survives through natural twinning or embryo-splitting. I doubt that many proponents of MSEHE would be willing to take the analogy with Parfit's discussion this far. But, again, many who find Parfit's discussion of survival and identity appealing still wish to preserve some role for physical continuity (they accept what he says about the split-brain cases, but not what he says about the teletransporter cases). Moreover, regardless of whether the attachment to physical continuity is rational, physical continuity is maintained in embryo-splitting.
Consider another example. Suppose that twinning in our hypothetical species often occurs during infancy. These infants have the same degree of sentience as human infants, but sometimes, during the first few days after birth, they cocoon and then split into two. If these infants are capable of retaining any experiences or memories, then their resulting twins retain these experiences and memories. But like human infants, their experiences and memories are limited; they lack both the ability and the opportunity to develop the relationships and personal history that would make twinning a social/legal headache in adult cases. Perhaps here we have something that parents could regard as at least as good as, or even better than, the continued identity of the original child.
Of course, this is all rather speculative. But I think it shows that we cannot easily infer that proponents of MSEHE do not take their own position seriously from the fact that they do not react to twinning in the same way in which they react to standard examples of death.Footnote 54
Moreover, since division is about as good as ordinary survival, we can easily make sense of the idea that a person who will be split, within mere minutes, has a right to not to be killed that is just as stringent as that of persons who are not facing immediate death. The person facing division has just as much to lose by being killed as anyone else. Does the same hold for a person who will become part of a fused hybrid within the next few minutes? Such a person has some share in the new individual's future; fusion may not be as good as ordinary survival or division, but perhaps it is better than a straightforward death.
B. Reactions to fusion
Discussing our reaction to fusion is difficult since it seems to be rare. Few persons will ever know whether they or their children are the product of embryo fusion. Thus, my thoughts in this section are even more speculative than in previous sections of this article.
Consider the possibility of previously split embryos fusing to form a single embryo. While it is difficult to see how we could know whether any given child is the result of such fusion, let's set this problem aside. Assume that we do not react with a sense of regret to the occurrence of this kind of fusion. Call this re-fusion.
Here the proponent of MSEHE cannot use Parfit's idea that survival as two is at least as good as survival as one. Surely, going from two embryos to one results in one if not both ceasing to exist or being destroyed. But this is not obvious. Consider this from the perspective of the individual embryos that end up being fused.Footnote 55 Each embryo is directed towards the construction of a complete adult human organism according to a specific genetic plan. Re-fusion does not disrupt or alter this plan, since the fused embryos share the same plan. Moreover, none of the individual embryos working according to this plan would have accomplished this simply by taking on more food and energy and growing larger. Rather, they would have accomplished this task by producing even more cells through further cellular division. Arguably, re-fusion simply provides useful material for the continuation of each embryo's project – further material from a very familiar source.
However, the fusion of separately fertilized ova, which results in a tetragametic chimera, is somewhat different in this regard. Such fusion does result, at least to some degree, in the frustration of the previous embryos’ projects. Since the two embryos worked from different genetic plans, and the resulting individual will combine different features from each of these plans, the chimera's life is purchased at the expense of two very different individuals who might have gone on to be fraternal twins. Here we have a loss of distinctiveness, not just a loss of numbers.
Consider some variations on my previous examples. One would not be surprised if members of an intelligent sentient species experienced a great sense of loss if their spouse blended with another person to form a single hybrid of the two. As with twinning, social institutions would have to adjust to make room for the occurrence of such fusions. But unlike cases of twinning, the problems of which are mostly practical, I think it inevitable that some sense of profound loss would remain in these cases. Likewise, one can easily imagine parents experiencing a great sense of loss if they watched two very distinct-looking children, even newborns, fuse to form a single hybrid of its predecessors.
Do we or should we react in something like this way to a person who turns out to be a tetragametic chimera? Presumably, Oderberg would call for some such reaction, albeit one that is diminished by distance in time from the event and the absence of social relationships with the previous embryos. Still, if we do not regard the life of a tetragametic chimera as something like the life of a person who owes his existence to the death of two innocent people, this seems to tell against MSEHE.
V. CONCLUSION
Once they are distinguished from other arguments against MSEHE, it becomes clear that arguments from twinning and fusion make little if any contribution to the debate over the EHE's moral standing. Simple appeals to twinning/fusion accomplish nothing, and the alleged multiplicity of the EHE does not prove that it lacks moral standing. Likewise, with the possible exception of tetragametic chimerism, reactions to twinning and fusion do not show that MSEHE proponents are inconsistent in their attitudes towards the EHE.
APPENDIX
As I noted earlier, Elizabeth Harman suggests that the dispute over twinning invites an appeal to Parfit's discussion of identity. However, her use of Parfit is quite different from mine. In her words,
In my discussion, I have assumed the relevant identity claim: when an embryo does develop into a person, there is a single thing that is first an embryo and then later a person. Some philosophers deny the identity claim because they are convinced of a psychological criterion of identity for persons. However, Derek Parfit (1984) has shown that what matters in survival does not coincide with identity; and in the face of his arguments, we should see that a psychological criterion is merely a good guide to what matters in survival, not to identity. Some philosophers hold that certain early embryos are not identical to any later-existing persons: these are embryos that are early enough to be capable of twinning. I do not understand why the mere possibility of twinning should be enough to undermine identity in a case where twinning did not actually occur. Had the embryo twinned, though it would have developed into two different persons, it would have been identical to neither. Nevertheless, if the embryo did actually develop without twinning, it is identical to the person it developed into.Footnote 56
I find Harman's appeal to Parfit somewhat confusing. She seems to invoke Parfit against those who wish to deny that adults and children are identical with their EHEs. But this cannot work. For Parfit, the continued identity of persons is a matter of psychological continuity on a one-to-one basis. Parfit's point is that what matters in our survival, psychological continuity, can be preserved even if psychological continuity is maintained on something other than a one-to-one basis – multiple successors and a loss of identity. However, for Parfit, the continuation of my identity is still a matter of having just one successor who is psychologically continuous with the me of today.
On Parfit's terms, my identity continues tomorrow, if tomorrow there is one individual who is psychologically continuous with the me of today. However, I am identical with my EHE in a morally relevant sense only if the very different connection between me and it is likewise a morally important one. Nothing about Parfit's discussion of identity provides any support for the moral importance of this connection. My use of Parfit aims to show that even if an embryo does twin, proponents of MSEHE can regard this as being as good as the ordinary survival of the EHE (continuing on as one developing embryo). They can do this by treating continuation of the original embryo's genetic plan in two successor embryos as analogous to a single sentient person's psychological continuity with two successors in fanciful examples such as Parfit's split-brain cases. This shows that proponents of MSEHE can regard the new twin embryos as legitimate survivors of the original. It does nothing to show that we as sentient persons should recognize a morally relevant sense of identity with our EHEs (twinned, fused or otherwise).Footnote 57
