singer p. 2007 with sagan agata about the moral status of stem cells

THE MORAL STATUS OF STEM CELLS

AGATA SAGAN AND PETER SINGER

Abstract: What moral status should we attribute to stem cells? To answer thisneglected question, we look in this essay at the properties of embryos and otherentities that could develop into beings who have uncontested moral status,namely, adult humans. Our analysis indicates that those who grant moral statusto embryos should also grant it to stem cells. This has implications that verge onabsurdity, since even if we were to try to do what we can to protect these entities,we would face the dilemma that the development of any embryo requires thedestruction of other potential beings. We respond to objections, including theclaim that the destruction of human embryos is wrong not because of the potentialof human embryos but because human embryos are actual beings with a rationalnature. We conclude that the more plausible position is to deny moral status toembryos, and thus to stem cells as well.

Keywords: cell, embryo, moral status, stem cells.

1. Introduction

Most ethical objections to the use of stem cells are directed at the use ofhuman embryonic stem cellsFin particular, at the destruction of humanembryos in order to obtain these cells. In an attempt to deect theseobjections, some have proposed ways of obtaining cells that have theproperties of embryonic stem cells but do not involve destroying embryos.One of these techniques involves taking a single cell from an embryo andusing it to generate an embryonic stem cell line, while the embryo cancontinue to develop unaffected by the removal of the cell (Lanza et al.2006). Another technique is to take cells from an embryo that we knowwill cease to develop soon, and so is in a kind of dying state anyway(Landry and Zucker 2004). A third proposal is to create defectiveembryosFfor example, ones that cannot form a placenta and so wouldnever develop into adultsFand take cells from them (Hurlbut 2004).A fourth is to induce parthenogenesis, so that an egg begins to developwithout any sperm and cells can be removed (Huanga et al. 2003).A fth proposal is to reverse the potency of more mature cells so thatthey revert to the same state as embryonic stem cells (Melton et al. 2005).

r 2007 The AuthorsJournal compilation r 2007 Metaphilosophy LLC and Blackwell Publishing LtdPublished by Blackwell Publishing Ltd, 9600 Garsington Road, Oxford OX4 2DQ, UK, and350 Main Street, Malden, MA 02148, USAMETAPHILOSOPHYVol. 38, Nos. 23, April 20070026-1068

r 2007 The AuthorsJournal compilation r 2007 Metaphilosophy LLC and Blackwell Publishing Ltd

These proposals have been criticized. Some question whether the effortput into developing these alternative methods is worthwhile, and raisequestions about how much use they are likely to be (National Institutes ofHealth Stem Cell Task Force 2005; Coalition for the Advancement ofMedical Research Dedicated to Advancing Stem Cell Research). Leavingaside for now the issue of whether those methods really avoid thedestruction of embryos, we want to ask a different question: Is thedestruction of embryos really the key ethical issue concerning the use ofhuman embryonic stem cells?

Embryonic stem cells are mainly derived from the inner cell mass of theembryo, from which the later stages of a human being develop. (Theremainder of the embryo contributes to the development of the placenta.)This inner call mass can, if moved to another trophoblast, develop into anadult. Do these cells perhaps have some moral status themselves,independently of the status of the embryo of which they once formed apart? This last question is not usually asked, because embryonic stem cellsare equated with other cells that have no special moral status (AmericanAssociation for Advancement of Science and Institute for Civil Society1999, 1112). Nevertheless, there are some who have put forward suchviews, among them Julian Savulescu and Ronald Bailey, and opponentsof the use of embryonic stem cells have responded to them (Savulescu,1999; Bailey 2001a, 2001b; Lee and George 2001a, 2001b). We will try togo further into this issue. To set the stage for that discussion, we need togive closer attention to the nature of embryos and to the question of whathuman entities can develop into a mature human being. Once we havedone this, we will consider to what moral status these human entities areentitled.

2. The Beginnings of Human Life

2.1. The Denition of the Embryo

The standard sense of the term embryo, in reference to mammals, isusually understood to refer to the entity resulting from the fertilization ofthe egg by the sperm, creating the zygote, until around the time whenorgans begin to form. Once the organs begin to form, the developingentity is usually referred to as a fetus until it is born, although sometimesthe term embryo is retained and fetus is understood merely as thename of a particular stage of development of the embryo. For a time, itwas common to refer to the embryo prior to implantation as a pre-implantation embryo, or, for short, preembryo. The latter term nevergained general acceptance, however, perhaps because opponents ofembryo experimentation thought of it as a specious attempt to denythat an embryo exists from the moment of fertilization.


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The term embryo is used in relation not only to mammals but also toother animals or even plants and can be used metaphorically to describeany initial stage of a development. Such uses are questionable. Moresignicant, for our purpose, is the opposite phenomenon that the absenceof a potential to develop does not negate the fact that an entity is anembryo. Although the very concept of something being an embryosuggests that it has the capicity to or is likely to, develop into some moremature stage or adult form, in practice the term is also applied to entitiesthatFperhaps because of some defect or because they have developed inthe fallopian tube rather than in the uterusFhave no possibility ofdeveloping to maturity. It seems that the term is used to refer to anymember of the class of entities that would, when normal and inappropriate circumstances, develop to the mature stage. Until recently,it was only in extreme cases, when the entity is severely abnormalFforexample, when it is a chaotic mass of cells resembling a teratomaFthatthere has been any uncertainty about whether to call it an embryo Now,however, the question What is an embryo? has been raised anew in thecontext of manipulations on entities that resemble embryos (Austriaco2005).

2.2. Do We All Begin at Fertilization?

Most of us think that we can trace our existence back to fertilization, butthis is not entirely accurate. Some humans, approximately 1 percent, areone of a pair of identical twins or higher multiples, and this gure is evenhigher if we include cases in which the other siblings die, perhapsundetected, during pregnancy. It is plausible to maintain that thesehumans begin to exist only when the embryo splits into two or moreembryos. Any other view leads to paradoxes about how two distinctindividuals can be said to have begun to exist at a time when there wasonly one individual. It has been suggested that in the case of an embryothat splits into twins there were two individuals present at the beginning.This may be defensible if the split is due to some factor internal to theembryo, but surely it is not if the split is caused by some external, perhapsentirely unpredictable, event.

In addition to these humans who are one of identical twins or highermultiples, there are othersFthe exact percentage is unknownFwhocome into existence as a result of the reverse process, that is, the fusingof two or more embryos into a single embryo. Then too we should saythat the human individual came into existence not at fertilization but onlyafter the fusing occurred. Otherwise we would have to specify which oneof the two or more embryos the human being was, and why that onesurvived fusing and the other, or others, did not. The parallel here to thesuggestion that in the case of an embryo splitting there were always twoindividuals would have to be the suggestion that in the case of embryos


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fusing there was always only one individual, located in two places. That isimplausible, and it becomes untenable if the fusing is a result of a causeexternal to the embryos.

The difculty of identifying the individual or individuals at this earlystage becomes even more acute if we consider splitting an embryo, thenfusing the split parts with parts of other embryos, then splitting themagain, and fusing them again, and so on.

2.3. Might We Begin Life as Something Other Than an Embryo?

To the best of our present knowledge, a single egg will not develop into amature human being. It will quite quickly cease to develop. Eggs, likesperm, have only half the number of chromosomes required for normaldevelopment. Even if the number of chromosomes is doubled, however,some of the genes will not be properly expressed unless the chromosomescome from specically an egg or a sperm. In mice, it has been shown to bepossible to produce a mature individual by joining two immature andappropriately altered eggs (Kono et al. 2004). This has renewed specula-tion about the possibility of parthenogenesis, but questions have beenraised about the results achieved with mice eggs. The same problem ofgene expression prevents sperm from developing, and in addition spermlacks cytoplasm, which is indispensable for growth.

What about other possibilities, some of which we mentioned abovewhen referring to possibilities that can occur in nature? A single cell canbe the beginning of a new being. We can, for example, take a two-cellembryo and isolate the two cells. Each cell will develop into a completeindividual. Only cells from the early stage of embryo development havethis ability; as the embryo develops, the cells lose it. Around the morulastage, they also become more compact and harder to separate, but groupsof cells may retain the ability to develop into a new being (Willadsen1979). If we cut the blastocyst (a later stage of the embryo beforeimplantation) into two halves, each half may develop, if it containsenough of both the inner cell mass and the trophoblast (Ozil 1993).

We do not know exactly how far into the process of development this ispossible. But experiments that have been conducted for many years showthat if we take a cell, or even just the nucleus of a cell, from a much laterembryo and transfer it to an egg from which the nucleus has beenremoved, this entity is capable of developing into a mature being (Will-adsen 1986). As Ian Wilmut famously showed with DollyFthe worldsrst cloned sheepFand as many subsequent experiments have conrmed,this can even be done if the cell is taken from an adult (Wilmut et al. 1997;Colman 1999). For ethical and legal reasons, experiments of these kindsusing human cells have not been continued beyond the point of im-plantation, but there is no reason to think that our species would be



signicantly different from other mammals in this respect (Stojkovic2005).

2.4. What Is Crucial for Development into a Being with Uncontested MoralStanding?

What, then, is crucial for the entity to be able to develop into a being thathas uncontested moral standing? It seems that there must be a nucleus,with the genes needed for development, and probably some cytoplasm.(The cytoplasmic components contain resources in addition to those inthe nucleus.) Everything else that is required seems to be the environmentin which life develops. With adults, there is usually no problem indeciding what is an entity and what is its environmentFhuman beings,and the air they breathe, for example, are clearly distinct. But during theearliest stages of human life, the distinction is less clear. How, forexample, does one draw the distinction in the case of the nucleus that isplaced in an enucleated egg? One possible test for these circumstancesFalthough it does not necessarily hold in other situationsFis to askwhether we could change something without changing the identity ofthe being so dramatically that it would no longer be the same being. (Westress dramatically because modifying a gene responsible for a diseaselike muscular dystrophy, for example, is a change in the entity but wouldnot be seen as changing the identity of the being, any more than losing alimb later in life would be seen as changing ones identity.)

If we transfer the nucleus to a different egg with different cytoplasm,does that affect the identity of the being who eventually develops? Somedifferences would be apparent, but we do not think they are identity-changing differences, any more than they would be if an embryo weretransferred to a different womans womb or a child were adopted at birthand reared in a different family.

At the moment we have no reliable adequate substitute for an eggscytoplasm except perhaps the cytoplasm of blastomeres from earlyembryos. (Perhaps whole polyploid embryos could also be regarded asa substitute, because although their cells have nuclei, those nuclei willmostly be eliminated during the development of the embryos [Nagy et al.1993]).1 One day, however, we may be able to develop a cell in a uid orsome other structure or even just by triggering appropriate genes in thenucleus (Takahashi and Yamanaka 2006; Silva et al. 2006). If thisbecomes possible, it will be more readily apparent that the cytoplasm isthe environment in which new life develops, rather than part of itsidentity.

1 For a distinct argument based on these experiments, see, for example, Silver 2006a,14143. For discussion, see Lee and George 2006b, Silver 2006b, and Lee and George2006c. See also the essays by Devolder and Ward and by Devolder and Harris in thiscollection.


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3. Stem Cells

3.1. Where Do Stem Cells Fit among the Possible Origins of a NewIndividual?

It is clear that even a single embryonic stem cell can, by the transfer ofits nucleus into an enucleated egg, be the beginning of a new humanlife (Wakayama 1999). Indeed, other stem cells (with the possibleexception of germ stem cells) can also be the beginning of a new humanlife, but it seems that embryonic stem cells, because they are not sodifferentiated, are better suited for cloning than any other cells. We arenot claiming that all cells have the potential to become maturehumans, because there are signicant differences between cells. We cando nuclear transfer with a nucleus from a terminally differentiated celllike an olfactory neuron or lymphocyte, but it is much less efcientthan when we use embryonic stem cells (Jaenisch et al. 2004; Hochedlin-ger and Jaenisch 2002). We cant do it at all with red blood cells, forexample, because they dont have a nucleus. There may also be otherkinds of cells whose ability to give rise to a more mature human being wedo not know about.

If something can develop into a new human being, should we think ofit as having the moral status of an embryo? If what is important is that anentity can become an adult human being, then should not that entity havethe same status as an embryo that can develop into a mature humanbeing?

One of us has argued elsewhere that, despite its potential, thenormal human embryo lacks the moral status that would give it a rightto life or require us to protect it from destruction (Singer 1993, chap. 6).Here, however, we are not arguing on the basis of that position.2 Rather,our point is that those who do think that the embryo is preciousbecause of its potential to become a mature human being seem to berequired to regard an embryonic stem cell as precious for the verysame reason. One could imagine differences in the value accorded tothe stem cell and the embryo, just as there could be differencesbetween the embryo and the newborn infant, but it would seem that ifthe human embryo has moral standing and is entitled to protection invirtue of what it can become, then the same must be true of humanembryonic stem cells. We can even imagine provisionally evaluating otherkinds of cells on the basis of their ability to support development tomaturity, with adult stem cells ranked below embryonic stem cells butabove somatic cells, unless further experiments show otherwise (Yang andCheng et al. 2006).

2 Indeed, this position is not entirely shared by Agata Sagan, who sees more signicancein the continuity of human development from earlier stages.



3.2. Implications of Granting Stem Cells Moral Status

If a new life is precious and entitled to protection, it seems that a minimalimplication of this is that we should, if other things are equal, protect thenew life from destruction and do our best to enable it to develop. What,then, would the inclusion of stem cells in the circle of precious entitiesrequire from us?

The most obvious implication is that we would not be permitted touse stem cells, no matter whether they originated from newlydestroyed embryos or from stem cell lines that have been in existencefor many years, or were obtained by some other method not involvingthe destruction of embryos at all. We would not even be permitted touse stem cells derived from adults, children, fetuses, or umbilical-cordblood. All these entities can develop into adult human beings. But thatis not all. Should we allow all embryonic stem cells to grow intoadults? If we accept that such entities are precious, then we wouldhave to take the same view of all the cells of the embryo. Should wethen split the early embryo and, when the resulting embryos havegrown, split them again? This process cannot be repeated indenitely,but when it can no longer be done, we could still, by means of nucleartransfer, use the cells of the embryo to allow as many of them as possibleto develop into adults (Stice 1993; Wakayama 2000). Should we also tryto locate all other cells in our body that have the potential to develop intomore mature human beings, take as many as possible, and enable them todo so? There are billions of such cells, and new cells are created in ourbodies all the time. Hence the number of possible new human beings whocould be created from just one human, while not literally innite, is sovast that it is difcult to name it without mathematical shortcuts.Multiplying it by the 6.5 billion people now in existence makes thisnumber even larger.

No society on earth, no matter how strongly it says it supports theprotection of human life, does any of this. We do not even considerourselves obliged to split the early embryo, which is an easy and reliableway of allowing its cells to develop into human beings. Nor do we supportresearch that will facilitate future attempts to allow all of these entities torealize their potential. We dont seriously entertain the notion of strivingto actualize the potential of every entity that could become an adulthuman being. But even if we would come to the conclusion, in the light ofwhat weve been discussing here, that our neglect of these entities iswrong, we would simply be unable to actualize the potential of morethan a tiny fraction of the already existing entities that could developinto adults.

Some may say that we should not interfere to save the lives of thepotential beings in an embryo, because we would then be killing theembryo, and it is prohibited to kill one innocent being in order to save


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others.3 We could, however, take some cells from an embryo withoutdestroying it. Or we could take a very large number of cells from an adultwithout causing any harm. (It is an interesting question, by the way, howmany cells we could take before we end up destroying the adult.) We maynot consider ourselves justied in killing one innocent human being tosave others, but we do justify taking some risks, even substantial ones,with human lives, if a human life will otherwise certainly be lost. (Forexample, we may drive an ambulance much faster than we wouldnormally consider safe.) Obviously, on the view we are consideringhere, when we contemplate taking cells from an embryo in order to allowthem to develop, if we decide not to do this, a human life will otherwise belost, in just the same sense that if we fail to protect a human embryo and itceases to exist, a human life will be lost.

Others may oppose any interference at all on the grounds that, asphysicians sometimes say, we should let nature take its course. But thisview implies an end to medicine as a whole, for all medicine is aninterference in nature. We would need to be told why we should carry out,at considerable expense, some life-saving medical proceduresFfor ex-ample, saving extremely premature infantsFwhereas there is no obliga-tion to perform others, such as saving the lives of cells that can becomemature human beings. Again, if having the potential to become a maturehuman being is what entitles the embryo to have its life protected, manyother cells are also entitled to have their lives protected.

Of course, in practiceFat least at the momentFit would be costly toallow all these entities to realize their potential. Cloning from adult cells,especially, is a demanding procedure, and even in animals is not yetentirely safe. There may also be objections to the loss of genetic diversitythat could result from extensive cloning from a small number of people ina particular area. The existence of so many identical beings may causepsychosocial problems as well, a sufciently important reason againstthat form of cloning. As for embryo cloning, whether by embryo splittingor by nuclear transfer using a nucleus from an embryonic cell, onlyembryos created in vitro could be considered for this procedure; fewwomen are likely to consent to the removal of an embryo from theiruterus so that it can be split and each of its cells can live. We already havehundreds of thousands of frozen embryos in reproductive clinics, so itwould be possible to split them without encountering the problem ofremoving embryos from the uterus. But the very fact that we already haveso many frozen embryos, and dont really know what to do with them,gives the idea of creating more of them a ludicrous air. Nevertheless, forthose who think that the embryo is precious and entitled to protection

3 On the debate about the distinction between killing and letting die, see Steinbock andNorcross 1994; Kuhse 1987, chaps. 24.



because of its potential to develop into a mature human being, the issueremains.

We are aware that many opponents of killing embryos are alsoopposed to in vitro fertilization, or to the creation of surplus embryos.Once the embryos exist, however, if they are precious and must beprotected, it should not matter how they were created. Others will thinkthat cloning is against Gods law and hence forbidden (Congregation forthe Doctrine of Faith 1987, part 1, sec. 6), but that will not move thosewho do not share that particular religious belief. In any case, a prohibi-tion on cloning does not exclude other things we could do to enableentities to develop into more mature human beings, including taking cellsfrom embryos that are lost during the natural course of development. Ithas been estimated that 30 percent of embryos created by sexualintercourse spontaneously miscarry (Wilcox et al. 1988). It is not incon-ceivable that research could enable us to retrieve these embryos andenable them, or their constituent cells, to live and develop into maturehuman beings. Yet those who regard embryos as precious do not suggestthat such research is a high priority.

4. Objections

4.1. Was Dolly Ever a Somatic Cell?

In a recent essay, Patrick Lee and Robert George (2006a) have respondedto claims that are in some respects similar to those that we havemade above. It is worth quoting the key passage of their argument,both in order to show why it fails to rebut the claims it addresses, andalso why the claims we have made are signicantly different. Lee andGeorge write:

[I]t is simply false to say that a somatic cell has the potential to become amature whole human being. In the cloning process, the somatic cell (or itsnucleus), which is part of a larger organism, ceases to be, and its constituentsenter into the make-up of a new and distinct organism, a new member of thespecies that is cloned (e.g., sheep, mouse, or human, if that should occur). Bycontrast, when the embryo grows, it continues to be, and simply matures. Youand I once were human embryos, just as you and I once were adolescents,children, toddlers, infants, and fetuses. But a cloned animal organism, such asDolly the sheep, never was a somatic cell, and so too a cloned human beingwould not come to be until the cloning process was successfully completed.Thus, a human embryo does, but a somatic cell does not, have the potential-ityFin the sense of active disposition and intrinsic powerFto grow (indeed, toself-develop) toward the mature stage of a human being.

There are several problems with this argument as a response to what wehave said here. The passage is directed to cloning from somatic cells, andthus does not address some of the possibilities that we have mentioned,such as nuclear transfer using nuclei from embryonic cells and other


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methods of creating new individuals that blur the signicance, for presentpurposes, of the boundary between somatic cells and other cells.If we split a two-cell embryo into its two constituent cells, each of themwould have been the original cell that existed before the split. In any case,even if we consider somatic cells, it isnt clear to us, as we have tried toshow, that we are justied in asserting that Dolly never was a somaticcell. There are different modes of reproduction, and they requiredifferent judgments about what was, or was not, something else.Suppose a friend admires my potted pelargonium. I break off a shortpiece of stalk, with a leaf or two on it, and put it into some potting mix.Nine months later, on my friends birthday, I present her with aourishing, blooming pelargonium that has grown from the cuttingI took. Was this plant ever the stalk with its leaf or two? We think itwas. But is that so different from saying that Dolly was once the somaticcell? Of course, the somatic cell needed an enucleated egg for it to develop,but the stalk needed potting mix and regular watering, and some cuttingsare more likely to develop if dipped in a hormone to stimulate rootgrowth. With plants, we have no difculty in seeing that they havedifferent ways of reproducing, including sexual reproduction throughseeds and asexual reproduction through taking cuttings. That we do morewhen we clone a mammal does not mean that we are adding somethingthat was not there before. There is no inherent reason why the sametwo different modes of reproduction cannot exist in humans as well, andif they ever do, we may well come to see the child as having once beenthe somatic cell from which he or she grew, just as we now see thepelargonium as having once been the stalk.

To the objection that the new plant didnt exist until we cut off thepiece of stalk, we can respond that it is not so clear whether separation isnecessary for being a distinct individualFthink of conjoined twins, forexample. We should also be aware that an adult body is continuouslyreleasing thousands of cells (for example, during sneezing), so insistenceon physical separation as a criterion for the existence of a distinctindividual may not avoid the problem of protecting the many potentiallives constituted by all these cells.

4.2. What Kind of Potentiality Matters?

There is, however, a more fundamental problem with the basic argumentthat Lee and George present, even as applied to somatic cells. Theyappeal to a special sense of potentialityFparsed as active dispositionand intrinsic powerFto distinguish the embryo from the somatic cell.But they need to show not just that this is a possible way of understandingthe concept of potentiality but also that it is the morally relevant way ofunderstanding it. Should the answer to the question Is it wrong todestroy an entity that has the potential to become a more mature



human? depend on whether or not the potential is that of an activedisposition and intrinsic power, or is a potential that only becomesactive after scientists take some crucial steps?

Before we address this question, we should note that in the specic caseof the embryos that would be destroyed to obtain stem cells, thedistinction Lee and George are seeking to make is more difcult todraw than they appear to realize. The embryos used by scientists to obtainstem cells are mainly surplus embryos produced during in vitro fertiliza-tion. There are hundreds of thousands of them, as we have said. Very fewof them will have a chance to develop into mature human beings. For thisto happen, there must be a woman willing to accept into her body anembryo that is not genetically related to her or to her partner. Scientistsmust then carefully thaw the embryo and transfer it to the womansuterus. The intrinsic power of the embryo in these circumstances isimpotentFin other words, there is no such powerFwithout modernmedical technology, and it can only self-develop with assistance fromthat technology. There is therefore not such a sharp distinction as onemight at rst think between the intrinsic power of the frozen embryoand that of the stem cell. Lee and George might respond that the existenceof frozen embryos outside the womb has created this unusual situation,and that we should not use it to assess the intrinsic power of embryos in amore natural situation. But as we have already noted, there is nothingunnatural about embryos failing to implant and being ushed out of theuterus, and once we know that this happens, and have the ability topreserve such embryos, we face an ethical decision about whether we havean ethical obligation to do so.

Opponents of embryo research have encouraged women to adoptunwanted frozen embryos and carry them to term. They gave thisinitiative the name Operation Snowake, recalling President GeorgeW. Bushs remark in his speech rejecting federal funding for researchon stem cell lines that were not already in existence: Like a snowake,each of these embryos is unique, with the unique genetic potentialof an individual human being (Bush 2001). In May 2005, and again inJuly 2006 when he vetoed a bill that would have funded research on stemcell lines derived from surplus embryos, President Bush posed for photosholding babies born as a result of Operation Snowake (Bush 2005,2006). The appeal of the photo opportunityFand of Operation Snow-ake itselfFis, of course, the idea that these babies would not haveexisted if the embryos from which they developed had been destroyed.But that would also be true if the babies had developed not from embryosthat resulted directly from the union of an egg and a sperm but fromembryos that were created by removing cells from an embryo. We caneven imagine an Operation Xerox Snowake that seeks to rescue notjust each cryopreserved embryo but also at least a few cells from eachembryo, so that still more of these babies can be born.


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4.3. Is the Embryo, but Not the Stem Cell, a Distinct Individual with aRational Nature?

Notwithstanding their argument that the potential of the embryo isdifferent from the potential of the somatic cell, ultimately Lee andGeorge assert that the embryo has a right to life not because it is apotential human being but because as a matter of basic biological facthuman embryos are actual human beings in the earliest stages of theirnatural development (2006a). To support this claim, they seek to draw aline between what is and what is not a human being in a way that does notimply that every cell that could become a human being is also an actualhuman being. Hence the discussion of potentiality that we considered inthe previous section. We shall now examine their defense of the claim thatembryos are actual human beings, to see whether their position isdefensible and whether it can avoid the implication that stem cells arealso actual human beings.

4.3.1. What entities have a rational nature? The nal two paragraphs ofLee and Georges essay give the crucial steps in their argument:

Some entities have intrinsic value and basic rights and other entities do not.Such a radicalmoral difference logically must be based on a radical ontologicaldifference (that is, a radical difference among those entities themselves).And so the basis for that moral difference (a difference in the way they shouldbe treated) must be the natures of those entities, not their accidentalcharacteristics which involve merely quantitative differences, or differencesin degree. (By accidental qualities, we mean those attributes that do not helpto dene the nature of an entity. In humans, age, size, stage of development,state of health, and so forth are accidental qualities.) The immediatelyexercisable capacity to reason and make free choices is only the developmentof the underlying basic, natural capacity for reasoning and free choice,and there are various degrees of that development along a continuum. Butone either is or is not a distinct subject with a rational nature (the traditionaldenition of person). So, Singer is correct to say that the right to life mustbe based on what is true of the entity now, not just what is true of its future.But it is true of the human embryo now that he or she is a distinct individualwith a rational nature, even though it will take him or her several years fullyto actualise his or her basic, natural capacities so they are immediatelyexercisable.

Our conclusion: Every human being, irrespective of age, size, condition ofdependency, or stage of developmentFor the means by which he or she isproducedFis intrinsically valuable as a subject of rights and deserves fullmoral respect. (2006a)

An obvious question to ask about this passage is whether the notion ofdevelopment is sufciently distinct from the notion of potentiality tobear the weight here placed upon it. Given that we all agree that thehuman embryo in its present form cannot reason, has never been able to



reason, and will not be able to reason for a long time, or possibly willnever be able to reason, is it more accurate to say that the human embryois a distinct individual with a rational nature or to say that the humanembryo is a distinct individual with the potential to become a rationalbeing? In our view, the former description is misleading. The embryodoes not have a rational nature. What it has is the genetic coding thatmay, under favorable circumstances, lead it to develop into a being with arational nature.

As we have seen, Lee and George reject the idea that a somatic cellFincontrast to an embryoFcould be a distinct individual with a rationalnature. But if having the genetic coding to develop, under favorablecircumstances, into a being with a rational nature is crucial to thewrongness of killing, then our earlier account of the different entitiesthat can become a human embryo shows that some unusual entities havethis property. Lee and Georges position implies that these entities areactual human beings with a right to life, and in need of medicalintervention to save their lives. We doubt that Lee and George wouldwant to take this view.

Perhaps Lee and George would respond that the entities we havereferred to as capable of developing into a mature human being do nothave the active disposition or intrinsic power to self-develop intosuch beings, and hence are not now beings with a rational nature.But suppose we have an embryo that, because of a genetic defect, willnot develop into a mature human being. Would Lee and George saythat for this reason it is not a distinct individual with a rational nature?If so, they would be opening a path to destroying such embryos, in orderto create stem cells lines from them. Indeed, it would seem to followthat they would have to accept the legitimacy of doing this, even if we alsohad the means to remedy the genetic defect and make the embryocompletely normal, for it would still be the case that the embryospower to develop was not intrinsic to it, and it was unable to self-develop. Again, we doubt that they would want to take this view. But itseems that they must take either this view or the one sketched in theprevious paragraph. They must therefore either agree that we have anobligation to preserve the lives of all entities with the potential to developinto mature humans, or accept the destruction of embryos with remedi-able defects.

4.3.2. From the factual claim to the moral claim. So far, we have exploredthe implications of Lee and Georges position on human embryosbut have not asked whether it is soundly based. If it were, we mighthave to accept it, even if it leads to some surprising consequencesregarding some cells that we do not normally think of as having aright to life. But even if we were to accept Lee and Georges ontologicalclaim, that would bring us no nearer to the moral conclusion they set


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forth in the nal paragraph of their essay, that the embryo is intrinsicallyvaluable as a subject of rights and deserves full moral respect. For if wedene rational nature as they dene it, we can still resist the claim thathaving a rational natureFin the sense in which they are using thetermFsufces for being a subject of rights, or being intrinsicallyvaluable, or deserving of moral respect. Rather, it would seem that themorally relevant characteristic on which such claims of value should bebased is the immediately exercisable capacity to reason and make freechoices.Why do we say this? Consider the grounds on which we may hold that

gratuitously killing a being like us is an especially grave wrongFthatis, a wrong that far exceeds any wrong we may commit in gratuitouslykilling a dog or a pig. (We will not here discuss the claim that it is simplymembership of the species Homo sapiens that makes it worse to kill thehuman being. One of us has argued elsewhere against this view [Singer1993, 2001], and Lee and George, to their credit, do not defend it.) Wemight say that to kill a being like us is an especially grave wrong because itinvolves the violation of the autonomous will of the being who is killed.Or we might say that it is an especially grave wrong because it thwarts thehopes and desires that beings like us have for the future, and typicallyrenders vain much of what they have been doingFstudying, training,saving their money, preparing to have children, and so onFin theexpectation that they will have a future. But it is not a beings rationalnature in the Lee and George sense that gives rise to a violation ofautonomy or the thwarting of hopes and desires for the future. Rather, itis the immediately exercisableFor at least, to take account of cases oftemporary unconsciousness, previously exercisedFcapacity to reasonthat is required for killing to have these effects. This strongly suggeststhat these aspects of a persons existence are more relevant to thewrongness of killing than whether the being is of such a nature that itwill eventually be able to exercise a capacity to reason.

When Lee and George assert that a radical moral difference betweenentities that have intrinsic value and basic rights and entities that lacksuch value and rights must be based on the natures of those entities, nottheir accidental characteristics, they beg several questions. They seem toassume a sharp dichotomy between, on the one hand, beings that haveintrinsic value and basic rights and, on the other hand, beings that lacksuch value and rights. Such a dichotomy may be convenient for law andpublic standards of ethics, but we should not assume that it exists innature. We may grant that rocks have no intrinsic value or basic rights,and that beings capable of exercising a capacity to reason do have bothintrinsic value and basic rights, but there are many intermediate cases.The gradual development of the embryo, fetus, and child suggests oneground for the existence of intermediate cases, but even for those whothink that the human embryo is already a being with a rational nature,



our knowledge of human evolution makes it is implausible to believe thatthere was a sudden leapFin a single generation?Ffrom beings with nointrinsic value or basic rights to beings with the intrinsic value and basicrights that normal mature human beings have now. Evolution is a gradualprocess that takes place over millennia, and there must have beenintermediate cases between our nonrational ancestors and our rationalones.

The growth in the creation of chimeras and hybrids will raise furtherdoubts about the idea of a dichotomy, rather than a continuum, betweenbeings with a rational nature and beings without such a nature. Actualand possible chimeras and hybrids include, for example, a sheep with onehuman gene, a complete human nucleus inside an enucleated rabbit egg,and a chimpanzee-human hybrid (Schnieke et al. 1997; Chen et al. 2003;Wikipedia no date). We have no trouble in classifying sheep with onehuman gene, but what about a human nucleus in an enucleated rabbitegg? Even if it could not develop into a mature human being, is it notcomparable to a human embryo with a defect that will prevent it fromever actually having the capacity to reason? If a human embryo is, fromthe beginning, a being with a rational nature, and for that reason has therights and intrinsic worth due to all human beings, is that status to benegated by the fact that it has a disability, even one so severe that it willnever develop into a mature being? If not, why should we not say the sameabout the human nucleus in the rabbit egg? What, nally, about achimpanzee-human hybrid who could, in the view of some scientists,even grow to adulthood?

More signicantly, the question of whether a given characteristicdenes the nature of an entity or is accidental to it cannot be used asan argument that seeks to answer the question, What kind of beings haveintrinsic value and rights? First we must decide what kind of being hasintrinsic value and rights, and only then can we say what characteristicsdene its nature and what are accidental to it. We must not here say, Wealready know that all and only human beings have intrinsic value andrights, so the answer is that you must be a human being. That assumesthe conclusion that Lee and George need to establish. There may be betteranswers. We might, for instance, answer that it is conscious beings whohave intrinsic value and rights. Or we could say that it is self-awarebeings, or beings with an exercisable or previously exercised capacity toreason, who have this special moral status. If we give such answers, thenthe nature of the entities that gives them intrinsic value and basic rightsjust is their consciousness or self-awareness or exercisable or previouslyexercised capacity to reason, and these things are not accidental to thatnatureFthey are its dening characteristics. Being human, on the otherhand, or having a particular genetic code then becomes accidental, sinceconscious and self-aware beings do not have to be human or have anyspecic genetic code. Lee and George simply assume that we must be


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looking for the kind of nature that persists through all stages of abeings biological life, and they label some features as accidental fromthis perspective. Why they make this assumption is a matter of specula-tion, but it may be because they began their quest already committed tothe conclusion that all members of the speciesHomo sapiens have intrinsicvalue and basic rights.

5. Conclusion

Once we understand the full range of biological possibilities of producingnew human beings, we have a new perspective on the beginning of life.These biological possibilities raise particular difculties for the claim thatthe embryo should be protected because it has the potential to become amore mature human being. To cling to this view, we would have to takeseriously all its far-reaching implications and make choices over a vastnumber of potential human lives.

How would we make such choices? One possible answer is that, in aworld with more than a billion people living below the World Bankspoverty line, and millions of people dying every year from poverty-relatedcauses, any prima facie obligation we might have to facilitate thedevelopment of additional human beings is overwhelmed by the factthat they would compete for scarce resources with those who already existand would add to existing pressures on the natural environment. If,however, we believe that we should protect at least some of those entitieswith the potential to become mature human beings, how are we to decidewhich ones to protect? If we have an abundance of normally developingcells and enough prospective parents who meet all the normal require-ments of providing a good home for their children, what other criteriashould we use? Some people will not be comfortable with making suchchoices, on a large scale, especially when the choices will be betweenidentical cells from the same embryo or adult, and we have to decidewhich among them will live and which will not. But not choosing is a kindof choice too, because it means that the cell will never develop as it could.Not choosing means that a possible human being will not exist.

These implications amount to something very close to a reductio adabsurdum of the claim that human embryos must not be destroyedbecause of their potential. It is, if not strictly a logical absurdity, at least aposition that no one could seriously set out to put into practice.

Finally, we have considered and rejected one argument for the viewthat the human embryo is not merely potentially but actually a being ofintrinsic value with basic rights. There may be other arguments for thisposition that we have not considered, but it is a position that is not goingto be easy to defend.

The most obvious way to avoid the difculties we have considered is toturn to the alternative view that at the beginning of life human entities



lack the requirements for moral status. They lack not only thoseattributes that are linked to personhood, like self-awareness, but alsomore basic things, like sentience or the capacity to feel pain. Thereforeunless there is some other reason to keep them aliveFfor example, thewishes of their parentsFwe may use them as we please. There are many,among them even some arguing from a theological perspective, whobelieve that even if embryos have some moral status, we would still bejustied in using them for research purposes if that research couldadvance our knowledge in a way that would lead to cures for diseasesthat afict millions (Hudson, Scott, and Faden 2005, 15; Peters 2001;Peters and Bennett 2001). We do not need to consider this claim. Themore plausible view, in our judgment, is that human entities at thebeginning of life do not have moral status, and hence the use of them forresearch purposes is justiable. Moreover, because this research couldlead to cures for diseases that are now fatal, it might even be obligatory.

University Center for Human ValuesPrinceton University5 Ivy LanePrinceton, NJ [email protected]@princeton.edu

Acknowledgments

We thank Lori Gruen and Laura Graber for their work on this essay. Wealso thank Elizabeth Harman, who was the commentator at a seminar atthe Princeton University Center for Human Values at which the essay wasdiscussed, and others who participated on that occasion or who were kindenough to read and give us comments on a draft of it, as well as otherswho saw the essay under other circumstance.

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singer p. 2007 with sagan agata about the moral status of stem cells

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