Human Embryo Metaphysics and the New Biotechnologies

Much of Christian scholarship has defended the Conception View of personhood, the idea that human beings have intrinsic value that begins at conception. However, modern reproductive technologies have led to new scientific insights into human embryology, without a matching increase in our metaphysical and moral understandings. A rigorous formulation of human nature and personhood is therefore needed. This paper explores and defends an ancient yet still prominent framework for human identity called hylomorphism, updated to match our current biological understandings and biotechnological innovations. In particular, we apply this framework to the ethical analysis of several kinds of new research, including a controversial intervention that treats mitochondrial diseases. We conclude with reasons why this understanding is crucial to the most prominent Christian understanding of human dignity. Dennis M. Sullivan is Professor of Pharmacy Practice and Director of the Center for Bioethics at Cedarville University. Tyler M. John is a pre-doctoral student and a Cedarville University alumnus.

Introduction

Human nature is at the core of human ethics and morality. Much of Christian scholarship has defended the Conception View of personhood, the idea that human beings have intrinsic value, beginning at conception. However, the modern era of reproductive technologies has led to an explosion of new scientific insights into human embryology, without a matching increase in our metaphysical and moral understandings.

If Christians are to support the Conception View in the academy in the context of these new findings, a rigorous formulation of human nature and personhood is essential. Christians must be equipped to offer insights from Scripture in discussions with other Christian scholars, but they must also articulate the Conception View in the face of secular objections. They should be able to argue for these foundations from the perspectives of philosophy and medical science, without always inextricably invoking biblical authority. This paper explores and defends an ancient yet still prominent framework for human identity called hylomorphism, updated to match our current biological understandings and to fit within the context of new biotechnological innovations. In particular, we will apply this framework to the ethical analysis of several kinds of new research, including a controversial intervention that treats mitochondrial diseases. We will conclude with reasons why this understanding is crucial to a Christian understanding of human dignity for our time.

The Biological Context

Early human embryos are the target of ongoing research, in order to fill the demand for pluripotent stem cells and to treat certain intractable genetic diseases. Some definitions will help the reader to understand the salient features of such embryos. Union of male sperm and female ova through fertilization creates a new human entity, a zygote, or one-celled embryo. After about 30 hours, the zygote divides into two cells, beginning the embryonic stage of development, lasting eight weeks (from eight weeks until birth the developing human entity is referred to as a fetus). Early stages of embryonic development include a solid ball called a morula (at three days), and a hollow cluster of cells with an inner cell mass, called a blastocyst (at five days). Implantation into the inner wall of the uterus (womb) takes place at about six and a half days after fertilization.¹

Stem cell research depends on pluripotent stem cells, such as those found within a human blastocyst. The term pluripotent, from the Latin for “many powers,” refers to the embryonic cells that serve as the precursors for the various tissues and organs of the human body. Such cells, removed from their embryos of origin and grown in laboratory cell culture, could possibly be transformed into various reparative tissues, with the goal of treating heart disease, Parkinson’s, diabetes mellitus, and other chronic disabling disorders. The fact that such treatments are still only a future possibility has not diminished the strong public pressure to promote and fund embryo-destructive research. The research relies on the use of frozen embryos left over from reproductive technologies that help childless couples to conceive. Specifically, such embryos are the result of in vitro fertilization (IVF) treatments, where conception takes place in a Petri dish.

It is difficult to get good estimates of the numbers of human embryos in cryogenic storage in the United States, with widely divergent estimates between 400,000 and 600,000.² Regardless, only a small percentage of these are available for research, perhaps as few as 3%. The rest are held in reserve for possible future implantation by the couples that created them. There has therefore been a strong research demand for other sources of pluripotent stem cells. One way to meet this demand would be to employ the technique of somatic cell nuclear transfer, also known as human cloning, which creates a human embryo in the absence of egg-sperm fusion. This technique involves retrieval of human oocytes from female volunteers. Each oocyte is then enucleated, that is, its haploid nucleus (23 chromosomes) is removed. This empty shell of an oocyte is called an ooplast. Then a diploid nucleus (46 chromosomes) from a human fibroblast is inserted into the ooplast (fibroblasts are normal components of the outer skin of adults). Subsequent electrical stimulation of the resulting entity may then cause it to begin dividing.³ The successful completion of this project will produce a human embryo, identical in kind to an embryo resulting from egg-sperm fusion.

Until recently, human cloning has not been technically feasible. However, in January of 2008 California researcher Samuel Wood reported in the journal Stem Cells that he had produced cloned human embryos, starting with donated eggs and adult skin cells. He was able to cause three of these embryos to develop for several days, and confirmed that they were the successful result of cloning by DNA analysis.⁴ However, it was not until July of 2013 that cloning resulted in actual tissue cultures that could be used to research various therapies.

In the most recent study, few of the resulting embryos developed past the eight-cell stage. In those few that did, the inner cell masses of the resulting blastocysts were either very small or were not seen at all. Despite these defects, the cloned embryos were able to produce pluripotent stem cells.⁵ There is therefore little doubt that they exhibited the characteristics of human embryos.

Human cloning produces human organisms. It would be highly metaphysically suspect to claim that cloning is a different procedure than other methods of producing embryos, and therefore does not produce a human being as other methods of producing embryos do; the resulting embryonic entity is intrinsically identical. The President’s Council on Bioethics has stated: “the blastocyst stage that develops from [a] one-celled cloned embryo will be the same being, whether it is then transferred to a woman’s uterus to begin a pregnancy or is used as a source of stem cells for research.”⁶ To be clear, no research group currently endorses human cloning as a reproductive technology.⁷ The sole impulse for human cloning is as a source of embryos for stem cell research. Furthermore, new procedures are now available that rely on cloning technology, such as the induction of pluripotency from adult fibroblasts,⁸ as well as the treatment of mitochondrial diseases through three-person embryos.⁹ Are the entities that result from such techniques human embryos or something else? Philosophical considerations will help to address these issues.

The Philosophical Context

What is a human embryo? Is it an organism, a single entity unified across time? Philosophically, these are ontological questions. Ontology is the branch of metaphysics that deals with the nature of existence and being.¹⁰ In this report, our approach to answering these questions derives from hylomorphism, an ancient doctrine about the ontology of living organisms that is, for many who hold to the Conception View, foundational to embryo metaphysics and to moral reasoning about early embryos.

Hylomorphism is not an inherently religious, let alone Christian, doctrine; it was expounded originally by Aristotle independent of any theological commitments. Yet it has a long history of adoption and adaptation by Christian thinkers, notably Thomas Aquinas and a long succession of Catholic Thomists along with some Protestant philosophers and theologians right up to the present. Hylomorphism claims that a living entity’s ontology is determined by its “first act” or animating principle, known by Aristotelians and Thomists as “the soul.”¹¹ In this regard, the soul need not be a spiritual entity, but might simply be, after Aristotle, “the form of a natural body having life potentially within it.”¹² The hylomorphic soul is that substance or principle that gives chunks of matter their organismal unity, life, and directedness toward a telos (purpose).

Whether or not one conceives of the soul as a separate ontic entity from the body (a la dualism), or, after Aristotle, the form of the matter making up the body, hylomorphic considerations help ground the integrated unity of ensouled organisms, the concept known as substance. Biola University professors J. P. Moreland and Scott B. Rae define substance as a distinct unity of essence that exists ontologically prior to any of its parts.¹³ The soul unifies an organism and causes it to persist from one moment to the next. Therefore, as applied to individual organisms, each is numerically identical to her former self – the thing that she once was is the very substance she is now. This is true whether or not the individual component cells of her body have been replaced, even many thousands of times. On hylomorphism, an organism is a unity of body and soul, and is thus more ontologically substantial than the mere sum of her organic parts.

Human identity on a hylomorphic view is strikingly similar to a newer formulation of identity in philosophical literature: the Organism View (OV). The OV, like hylomorphism, derives from Aristotelian philosophy, and is held prominently by Eric Olson¹⁴ and Matthew Liao.¹⁵ On the OV, human persons are essentially organisms. So you and I came into existence when the human organism with which we are identical came into existence. Persons persist through time as continuing organisms.¹⁶

Both views hold that a person is identical to some unified, embodied, self-directed entity with its own internal program. A complete defense of these views would be beyond the purview of this paper, but it is important here to outline the similarities between hylomorphism and the OV. According to Liao, the OV states that a being X is essentially an organism if and only if:

a) X begins to exist when the capacity to regulate and coordinate metabolic and other life processes is there; b) X persists as long as there is what may be called ‘organismic continuity,’ which is the continuing ability to regulate and coordinate metabolic and other life processes; and c) X ceases to exist when the capacity to regulate and coordinate metabolic and other life processes is permanently gone.¹⁷

We would propose that points (a) and (b) are compatible with a Thomistic hylomorphic view of human identity, in that they accurately describe important aspects of ensouled human existence. Point (c) is useful as a descriptor of organismal physical unity until death; however, Christian hylomorphism claims that ensouled persons survive their death.

Thus, given that one caveat, the key features of a human person on the OV are her inherent capacity to regulate and coordinate life processes, her persistence by regulating and coordinating life processes, and her death by losing her capacity to regulate and to coordinate life processes.¹⁸ These life processes provide an organism with her unity as a functioning whole and her self-directedness toward her telos. These essential features of identity on the hylomorphic and OV are the same up until the moment of an individual’s death. Since these views make identical claims about when we began to exist, they are therefore interchangeable in all ways relevant to our project here (Olson himself does not hold to hylomorphism, but admits that it may be compatible with his view¹⁹). The same biological and metaphysical features that give an organism its identity give a hylomorphic body-soul unity its identity. We will assume this throughout the remainder of this paper, as we delineate the salient biological features that provide human persons with their own organismic/hylomorphic continuity.

As the above suggests, the OV and hylomorphism offer a strong metaphysical foundation for the Conception View. To better appreciate the important implications of these views for human personhood better, we can look to a contrasting idea. Opponents of the Conception View claim that that the conditions of personhood are something other than simply the formation of a human organism with coordinated and self-directed life processes. Most often, this means that a human person comes into existence at some point in time after the formation of his or her respective zygote. Some opponents of the Conception View claim that human persons begin when their minds begin, or, alternatively, when the material brain structures capable of supporting their minds begin.²⁰ This has some intuitive plausibility. Since a majority of medical experts and philosophers accept brain death (death by neurological criteria) as the appropriate standard for when a human person ends (at least in the physical realm), it seems prima facie plausible to accept “brain birth,” that is, the development of a fetal nervous system in the unborn, as the appropriate criteria for when a human person begins.

To the contrary, embryologist Maureen Condic argues that the loss of integrated bodily function is what makes brain death the appropriate criterion for determining the loss of personhood in medical practice. From a strictly physical perspective, persons cease to exist when their integrated bodily function and coordinated life processes cease, just as they begin to exist when these processes begin.²¹ Embryos, we claim, are organic unities maintaining integrated bodily function and coordinated life processes. This is not, of course, due to coordination in the brain, which does not yet exist, but to the embryo’s genetically-determined internal program. This allows it to direct its own development, requiring nothing more than time and nutrition to arrive at the status of an adult member of the human species, complete with a rational brain. Thus, while more “functional” views of human identity do not lack plausibility, there is no reason to prefer them over the Conception View on these grounds. Hylomorphism and the OV hold up in their own rights, and give good reason to think that human beings come into existence long before their respective brain structures develop.

So, hylomorphic metaphysics and the OV entail that a human person is a substance/organism that persists through time as an internally coordinated and self-directed whole. At what point, then, do these views imply that we come into existence? We shall herein argue that, on the organism and hylomorphic views, the unity of the integrated substance/organism can be traced all the way back to union of sperm and egg at conception.

The Status of Early Embryos

To begin with, we must more clearly define conception. The lay term “conception” actually comprises two biological processes: fertilization, where sperm and ovum first come into contact, and syngamy, where male and female pro-nuclei unite to produce the 23 pairs of chromosomes characteristic of human life. These two processes are separated by several hours.²² Although some would argue that establishment of the genome in the nucleus at syngamy should be the beginning of human identity, Condic argues that a zygote’s coordinated internal integration implies that its identity begins at fertilization:

From the moment of sperm-egg fusion, a human zygote acts as a complete whole, with all the parts of the zygote interacting in an orchestrated fashion to generate the structures and relationships required for the zygote to continue developing towards its mature state….This coordinated behavior is the very hallmark of an organism.²³

If we take human fertilization as the starting point, is there any other evidence that the one-celled zygote and subsequent multi-celled embryo has a coordinated internal integration that makes it plausibly an organism, and not simply a collection of cells?

Condic has addressed this issue with clarity:

[O]rganisms (including single-celled human zygotes) are organized towards the production and maintenance of an integrated bodily system which is characteristic of the species. Since… the operations of a thing proceed from the organizing principle or form it has, an observed tendency to organize into a mature human being is a clear indication of a human form or soul.²⁴

As stated earlier, this organizing principle begins at the moment of sperm-egg fusion, which forms the human zygote. Shortly after sperm penetration, the ovum responds by making itself impenetrable to other sperm, a phenomenon known as polyspermy block. The ovum then carries out the rest of its differentiation by discarding excess chromosomal material to become a definitive oocyte. The remaining 23 chromosomes are arranged in a vesicular nucleus called the female pronucleus. This will eventually unite with the male pronucleus from the sperm at syngamy. The ovum also undergoes metabolic activation at this time, allowing it to extrude unneeded genetic material, and to carry out other steps necessary to cause syngamy. Within 30 hours of sperm-egg fusion, the first cell division takes place.²⁵

As discussed earlier, the embryo forms a solid ball of eight to ten cells called a morula at three days of development. At this stage, the individual cells (called blastomeres) can be considered totipotent (Latin for “all powers”), that is, each one is capable of producing any of the later tissues and organs arising from subsequent development. However, totipotency (to be distinguished from the pluripotency of a later stage) has caused a great deal of confusion in philosophical literature. The term does not mean that any individual cell of the three-day embryo can be removed and become an organism itself. Three-day blastomeres are not equivalent to zygotes.²⁶

Jason Eberl illustrates this confusion when he writes:

“Totipotency” means that, prior to implantation, each cell or group of cells has the power to separate from the rest of the zygote, divide by cellular mitosis, and develop into a multicellular organism. It is due to this totipotency of pre-implantation cells that identical twins, triplets, etc., are able to occur. One or more cells break away from the cluster, divide (mitosis), and develop into a second (or third, fourth, etc.) organism. Since each cell or group of cells is its own unique individual biological entity and has the capacity to separate and develop into a distinct multicellular biological organism, it cannot be said that there is already an individual human organism at this point. In potentiality, there are, practically speaking, one or a few individual human organisms present.²⁷

Thus, based on a misunderstanding of the embryology, Eberl claims that pre-implantation human embryos are not individual organisms. However, a three-day embryo is an integrated whole entity. Put another way, in certain types of stem cell research (ethics aside), a morula can be disaggregated into its component blastomeres, which can then be used to produce stem cell lines to treat certain diseases (much like pluripotent stem cells of the blastocyst). Such disaggregation destroys the embryo. Its internal coordinated development is lost in the process, and the organism dies.

Nonetheless, Eberl dismisses such early embryos as merely “cell clusters which contain human DNA,” with only “passive potentiality” at best. In this he borrows from Tooley’s idea of passive potentiality as referring to an entity that lacks certain “positive causal factors,” that would give that entity the ability to self-organize.²⁸ But, as we have shown, there is no evidence to support this claim.

As his statement above demonstrates, Eberl also supports his claim of passive potentiality by way of the so-called “twinning problem,” premised on the idea that no integrated organism exists until the possibility of twinning has disappeared. Monozygotic twinning occurs when two separate complete embryos arise from the spontaneous splitting of a single embryo. This usually occurs on or after the blastocyst stage, at least five days after conception, but may occur as late as 14 days. Some have claimed that such twinning militates against the existence of an enduring entity from conception, on the presumption that no identity relation can exist between the twinned entities and the original embryo. However, the identity relation is preserved if a complete individual is produced at fertilization and endures through the developmental process, while a separate new individual arises at the beginning of the split, with its own coordinated internal integration thereafter. Perhaps less plausibly, it might otherwise be the case that embryonic death occurs at the moment of the split, with two new organisms arising from it. As Snyder has summarized it, “the possibility of twinning is not inconsistent with moral standing for both the early embryo and its potential twin successors.”²⁹ Twinning is not a defeater of the Conception View.

The details of embryology make it clear, contra Eberl, that a zygote directs its own development, and that subsequent embryological stages are more than mere collections of random cells. If, as we have stated earlier, an integrated human individual exists at fertilization, from which a separate new individual can arise with twinning, then Eberl’s claim for personhood only after the potential for twinning seems arbitrary. If it is true that the zygote and early (pre-implantation) embryo have active potentiality, then the soul serves as the positive causal factor to make it an integrated whole from fertilization forward. We could say much more from the perspective of human embryology, but these comments should suffice to demonstrate the organismal nature of the embryo from its earliest stages.

Applications for Stem Cell Research and Human Cloning

If the preceding analysis is correct, then reproductive technologies such as IVF produce embryos intrinsically identical to those produced naturally, and embryos produced through human cloning are also the same sort of metaphysical entity. All are organisms, exhibiting persistence over time and numerical identity with later developmental stages. Though a complete argument for their moral status goes beyond the purposes of this paper, their organismal nature provides the basis for the Conception View of personhood. On this view, destroying an embryo for its stem cells is ethically illicit, because it kills a human being. This view also implies that embryo-destructive stem cell research, with embryos derived from either IVF or human cloning, is deeply immoral. Is there an alternative that still provides the presumed benefits of such research?

Induced Pluripotent Stem Cells

In 2007, two independent research teams: Junying Yu and colleagues from Madison, Wisconsin, and Kazutoshi Takahashi and associates from Kyoto, Japan, simultaneously revealed a truly innovative idea for creating pluripotent human stem cells. Both teams added four transcription factors to human skin fibroblasts, which created “induced pluripotent stem cells” (iPS cells). In both cases, the reprogrammed cells resembled embryonic stem cells in every measurable way, and demonstrated the ability to develop into all three primary germ layers.³⁰ Yet in no way do these cells have an individual telos; they lack any inherent capacity to coordinate metabolic processes, and are not organisms.

At first glance, this new technology seems to be the best outcome imaginable. Charles Krauthammer can perhaps be excused for some hyperbole when he writes:

[It is] one of the great scientific breakthroughs since the discovery of DNA: an embryo-free way to produce genetically matched stem cells. Even a scientist who cares not a whit about the morality of embryo destruction will adopt this technique because it is so simple and powerful. The embryonic stem cell debate is over…³¹

One reason for the excitement is that transplanted iPS cells may avoid the problem of tissue rejection, since they can be taken from a patient’s own skin cells, grown in culture, and then transplanted back without the risk of causing an immune reaction. Unfortunately, it is not that simple. The new techniques involve the use of viral vectors that themselves may induce immunity, and pluripotent cells have the potential to cause tumors in the recipients. At present, this kind of pluripotent stem cells “may be suitable for the study of disease mechanisms or for drug screening and validation, [but] they definitely are not suitable for cell replacement therapy.”³² There may be strategies to mitigate these problems, and this is the subject of intensive ongoing research.

So the stem cell debate is far from over. Technical problems associated with iPS cells may limit their utility. And funding and political considerations will make more traditional embryo-destructive research strategies desirable in the minds of researchers for many years to come. The Conception View, buttressed by hylomorphism and the OV, strongly opposes such strategies and commends continued efforts to develop alternatives such as iPS cell research.

The Newest Controversy: “Three-Person Embryos”

On February 24, 2015, Great Britain legalized the creation of so-called “three-person” embryos to treat certain mitochondrial diseases.³³ Though Britain is the first nation to approve this practice, the Institute of Medicine in the U.S. is also investigating its ethical feasibility at the request of the Food and Drug Administration.³⁴

Mitochondria are tiny organelles that serve as “powerhouses” of the cell, creating most of the energy needed for its metabolic activities. They are found out in the cytoplasm, away from the cell nucleus where DNA is stored. Nonetheless, mitochondria contain small amounts of DNA, normally less than 1% of the total. Most DNA is passed on to progeny through sperm and egg, whereas mitochondrial DNA is transmitted to embryos exclusively through the mother, via the cytoplasm of an egg cell.

Mutations in mitochondrial DNA can cause serious diseases that in some cases are fatal to offspring. Researchers have proposed transferring the nuclear genetic material from the eggs or zygotes of a woman affected with mitochondrial disease caused by mutations in mitochondrial DNA to an egg or zygote of a woman with normal mitochondria. As mitochondria are inherited solely from a mother through her eggs, this would in theory prevent maternal transmission of mitochondrial disease from the affected woman to her children. These modifications of eggs and zygotes would allow affected women to have genetically related children without passing on their mutant mitochondrial DNA. However, these children would have nuclear DNA from one man and one woman and mitochondrial DNA from another woman. Thus, any children born to women as a result of these methods would have DNA from three individuals.

Will embryos be destroyed in order to carry out this procedure? It depends upon how the procedure is carried out. There are several methods by which three-person embryos can be made, and not all are embryo-destructive. Using definitions from the Center for Genetics and Society,³⁵ pronuclear transfer would involve the destruction of embryos, but maternal spindle transfer and nuclear genome transfer would not.

The philosophical synthesis outlined in this paper should help to make clear the crucial differentiator in these techniques. On the view we have outlined, the unity of the integrated person can be traced all the way back to fertilization. The pro-nuclear transfer technique would start with two newly-fertilized ova, one from the parents with the mitochondrial disease, and the other from a donor. The pro-nuclei of both are removed before syngamy occurs, then the DNA from the affected parents is inserted into the leftover “shell” of the donor, thus producing a new embryo with the DNA of the parents but the normal mitochondrial DNA of the donor. As we have argued, human organisms come into existence at fertilization, prior to syngamy. Fertilized ova (zygotes) are internally integrated wholes with active causal powers that direct them toward a telos. Destroying them destroys two organisms to create another one. Those who hold to the Conception View of personhood would therefore object to this as immoral, claiming that persons (the two zygotes) were destroyed for their parts, in order to create a third.

The second technique, maternal spindle transfer, manipulates unfertilized human ova. It transfers the affected mother’s nuclear DNA into a healthy donor ooplast (an unfertilized donor egg with the nucleus removed). The newly-constituted ovum contains the affected mother’s DNA, but the healthy cytoplasmic mitochondria of the donor. Only at this time is the resulting egg combined with the male parent’s sperm, thus producing a child without the mitochondrial disease.³⁶ For Conception View adherents, this makes a big difference, for an organism is not destroyed in the process. The third method, nuclear genome transfer, is substantially similar to the process just outlined.

There are several other safety and ethics concerns in these relatively untested procedures, such as violating a European ban on modifying the human germline, risks to the women from whom eggs are extracted, and potential identity struggles that individuals might face once they learn of the unusual circumstances surrounding their conception. Thus, our intention is not to make a summary moral judgment on the creation of three-parent embryos in our society, but rather to show how our hylomorphic understanding informs the Conception View in its analysis of these developments. We claim that the Conception View implies that pro-nuclear transfer is in principle morally wrong, while maternal spindle transfer and nuclear genome transfer may be morally acceptable.³⁷

Conclusion

This paper has synthesized an ancient hylomorphic understanding of human beings with the more recent Organism View. In this synthesis, we have shown from modern embryology that the human being is an organism from fertilization onward, with a coordinated internal program that makes it capable, given time, nutrition, and a favorable environment, to direct its own differentiation and development into an adult member of the human species. We have considered objections to this thesis from totipotency and twinning to show that these are not defeaters of the view. We have then given careful consideration to human cloning, induced pluripotent stem cells, and the newly proposed “three-person” embryos to show how our perspective provides metaphysical clarity.

Our framework provides strong support for the organismal status of early human embryos, and gives a lucid foundation for the ethical permissibility of research on iPS cells, which are not human embryos, nor are they created from embryo destruction. For those who accept the claim that all human beings have moral status, it helps support the idea that such status even extends to human zygotes. On this view, cryopreserved and cloned human embryos are ethically off-limits as research material, and one form of mitochondrial disease treatment that uses components from early zygotes is also unacceptable morally.

Ultimately, there is much more at stake here than a narrow research agenda. How we are constituted is vital to understanding our human dignity. Gilbert Meilaender has put it this way:

An animal is not a bad thing, nor is an angel or a god. But we are none of these, and human dignity is to be found in the kind of life that honors and upholds the peculiar nature that is ours, even if there is no recipe book that can always show us how properly to unite and reconcile body and spirit.³⁸

Meilaender is very concerned about how our embrace of reproductive technologies has caused us to lose any sense of telos as constitutive of human nature. For him, purpose “is embedded at the heart of an organism’s – and certainly a human being’s – existence.”³⁹ Seeing the outcomes of our reproductive manipulations as organisms rather than as mere products will surely help to preserve the human dignity inherent in us all.⁴⁰

1. Gary C. Schoenwolf et al., Larsen’s Human Embryology, 4th ed. (Philadelphia: Churchill Livingstone/Elsevier, 2009); T. W. Sadler and Jan Langman, Langman’s Medical Embryology, 12th ed. (Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, 2012).
2. “How Many Frozen Human Embryos Are Available for Research?,” Rand Institute (2003), http://www.rand.org/pubs/research_briefs/RB9038/index1.html; “Embryo Adoption Awareness Center,” http://www.embryoadoption.org/; Geoffrey P. Lomax and Alan O. Trounson, “Correcting Misperceptions About Cryopreserved Embryos and Stem Cell Research,” Nature Biotechnology 31.4 (2013).
3. Andrew J. French et al., “Development of Human Cloned Blastocysts Following Somatic Cell Nuclear Transfer with Adult Fibroblasts,” Stem Cells 26.2 (2008); Masahito Tachibana et al., “Human Embryonic Stem Cells Derived by Somatic Cell Nuclear Transfer,” Cell 154.2 (2013).
4. French et al., “Development of Human Cloned Blastocysts Following Somatic Cell Nuclear Transfer with Adult Fibroblasts.”
5. Tachibana et al., “Human Embryonic Stem Cells Derived by Somatic Cell Nuclear Transfer.”
6. “President’s Council on Bioethics: Cloning,” Georgetown University, http://bioethics.georgetown.edu/pcbe/reports/cloningreport/terminology.html.
7. “About Reproductive Cloning,” http://www.geneticsandsociety.org/section.php?id=16.
8. William Hurlbut, “Altered Nuclear Transfer as a Morally Acceptable Means for the Procurement of Human Embryonic Stem Cells,” http://www.bioethics.gov/background/hurlbut. html; Kazutoshi Takahashi et al., “Induction of Pluripotent Stem Cells from Adult Human Fibroblasts by Defined Factors,” Cell 131.5 (2007); Junying Yu et al., “Induced Pluripotent Stem Cell Lines Derived from Human Somatic Cells,” Science 318.5858 (2007).
9. Center_for_Genetics_and_Society, “3-Person Ivf,” http://www.geneticsandsociety.org/article.php?id=6527.
10. James Porter Moreland and William Lane Craig, Philosophical Foundations for a Christian Worldview (Downers Grove, IL: InterVarsity Press, 2009).
11. Thomas Aquinas, “Summa Theologiæ,” http://www.ccel.org/ccel/aquinas/summa.pdf.
12. Aristotle, “On the Soul,” The Internet Classics Archive, http://classics.mit.edu/Aristotle/soul.2.ii.html.
13. J. P. Moreland, “Humanness, Personhood, and the Right to Die,” Faith and Philosophy 12.1 (1995); J. P. Moreland and Scott B. Rae, Body and Soul (Downers Grove: InterVarsity Press, 2000).
14. Eric T. Olson, The Human Animal: Personal Identity without Psychology, Philosophy of Mind Series (New York: Oxford University Press, 1997); What Are We?: A Study in Personal Ontology, Philosophy of Mind (Oxford; New York: Oxford University Press, 2007).
15. S. Matthew Liao, “Twinning, Inorganic Replacement, and the Organism View,” Ratio 23.1 (2010): 59-72.
16. The authors of this paper are entirely unsatisfied with the use of the word “person” here, as used commonly in moral philosophy. It would be more accurate to claim that, for human beings, the referent “I” can only rightly refer to a human organism.
17. Liao, “Twinning, Inorganic Replacement, and the Organism View,” 60.
18. For many who hold to the OV (notable exceptions are Peter van Inwagen, Trenton Merricks, and Matthew Liao), an individual goes out of existence at the moment of his death. For Christians, however, death is merely a transition point in one’s life.
19. Olson, What Are We?: A Study in Personal Ontology, 171-172.
20. J. M. Goldenring, “The Brain-Life Theory: Towards a Consistent Biological Definition of Humanness,” Journal of Medical Ethics 11.4 (1985); Jeff McMahan, The Ethics of Killing: Problems at the Margins of Life, Oxford Ethics Series (New York: Oxford University Press, 2002); Lynne Rudder Baker, Naturalism and the First-Person Perspective (Oxford; New York: Oxford University Press, 2013); Ibid.
21. Maureen Condic, “Life: Defining the Beginning by the End,” First Things (2003); Maureen Condic and Samuel Condic, “Defining Organisms by Organization,” The National Catholic Bioethics Quarterly 5.2 (2005).
22. Heide Schatten and Gerald Schatten, “The Cell Biology of Fertilization,” in Cell Biology (San Diego: Academic Press, 1989).
23. Condic, Maureen, “When Does Human Life Begin? A Scientific Perspective,” The National Catholic Bioethics Quarterly 9.1 (2009), p. 140.
24. Condic and Condic, “Defining Organisms by Organization,” 338.
25. Sadler and Langman, Langman’s Medical Embryology; Schoenwolf et al., Larsen’s Human Embryology.
26. Maureen Condic, “Totipotency: What It Is and What It Is Not,” Stem Cells and Development doi:10.1089/scd.2013.0364 (2014).
27. Jason T. Eberl, “The Beginning of Personhood: A Thomistic Biological Analysis,” Bioethics 14.2 (2000), 142.
28. Michael Tooley, Abortion and Infanticide (Oxford: Clarendon Press, 1983).
29. Evan Y. Snyder, Lawrence M. Hinman, and Michael W. Kalichman, “Can Science Resolve the Ethical Impasse in Stem Cell Research?,” Nature Biotechnology 24.4 (2006), 398.
30. Takahashi et al., “Induction of Pluripotent Stem Cells from Adult Human Fibroblasts by Defined Factors”; Yu et al., “Induced Pluripotent Stem Cell Lines Derived from Human Somatic Cells.”
31. Charles Krauthammer, “Stem Cell Vindication,” The Washington Post, November 30 2007: www.washingtonpost.com/wp-dyn/content/article/2007/11/29/AR2007112901878.html.
32. J. Yee, “Turning Somatic Cells into Pluripotent Stem Cells,” Nature education 3.9 (2010), 25.
33. Reuters, “Britain Becomes First Nation to Legalize Three-Parent Babies,” http://www.reuters.com/article/2015/02/24/us-health-babies-3parent-idUSKBN0LS2GH20150224.
34. Center for Genetics and Society, “3-Person Ivf.”
35. Ibid.
36. Ibid.
37. The authors are grateful to Heather Kuruvilla, Ph.D. (Department of Science and Math, Cedarville University) for helpful insights on this topic.
38. Gilbert Meilaender, Neither Beast nor God: The Dignity of the Human Person, 1st American ed. (New York: Encounter Books, 2009), 5.
39. Ibid., 29.
40. The authors are grateful for helpful suggestions in the preparation of this paper by Maureen Condic, Ph.D. (Department of Neurobiology and Anatomy, University of Utah) and J. R. Gilhooly, Ph.D. (School of Biblical and Theological Studies, Cedarville University). One of the authors (DMS) also gratefully acknowledges support through a Cedarville University Faculty Scholarship Summer Grant.