Background Material on the Scientific and Moral Status of the Early Human Embryo: The "Personhood" Debates

Dianne N. Irving
copyright June 1, 1994
Reproduced with Permission

Briefing to the United States Congressional Caucus (sponsored by Rep. Chris Smith), (RE: The NIH Human Embryo Research Panel), at the Rayburn Office Building, Washington, D.C., June 1, 1994. Other briefer, Dr. C. Ward Kischer, human embryologist, University of Arizona, Tucson, AZ.

I. Introduction*

The question of human embryo or fetal "personhood" - or when during human embryogenesis a human person begins (and therefore possesses moral status) - is currently one of the most pivotal - and confusing - issues in the abortion debates. It is also the question which NIH (and many others) refuse to address and resolve in their current discussions concerning the regulation of IVF and other human embryo research. Important overlap exists, however, between the pivotal issue of "personhood" and several other complex bioethics and public policy issues, e.g., fetal and fetal tissue research, genetic screening for diseases, sex, etc., the Genome Project - as well as with issues at the other end of life, e.g., informed and proxy consent, patients in a "persistent vegetative state", refusal or withdrawal of medical treatment, definitions of "brain death" and "brain life", organ transplantation, rationing or allocation of scarce medical resources and euthanasia, etc. If true "personhood" is present, then that person's rights are socially, ethically and legally protected1; if not, then he or she is perceived as "only" or as "less than" a human being (not a person) - and different social, ethical and legal norms or criteria take precedence2. There is a great deal at stake in clarifying and resolving all of these interrelated issues. It is hoped that the following discussion will be of some help in sorting out the arguments on "personhood", and stimulate others to examine the given "facts" - both scientifically and philosophically - more vigorously.

The various arguments for different biological marker events of "personhood" contain quite serious logical, scientific and philosophical flaws. As all three disciplines overlap considerably in these arguments, it is difficult to identify where the contributions of one discipline ends and the other begins. Yet it would seem that the scientific evidence used to support the various marker events claimed during human embryogenesis should be in agreement - at least within an acceptable range.3 Such an agreement is not found to be the case. Since the scientific evidence cited is usually the grounding rationale or the "major premise" in most of these arguments on "personhood", it is particularly important to be as sure as possible that the science used is "correct". Different conclusions about "personhood" follow from different sets of scientific evidence.

My main purpose is to point out briefly some of the serious discrepancies in the science used in these "personhood" debates.4 The impact of the questionable philosophy used will also be briefly noted. I would argue that in several instances it would seem that philosophical presuppositions have been imposed on the scientific data used in these arguments. Different conclusions about "personhood" follow from different philosophical definitions of a "human being" or a "human person". References are included to which one may refer for a more detailed treatment. A very rough sketch of the more significant philosophical considerations follow.

II. Philosophical Definitions of a "Human Being" or a "Human Person"

Two brief points concerning the philosophy used in these arguments are important to bear in mind: (1) different philosophical "schools" define a "human being" or a "human person" differently, and (2) the philosophical terms of "potency", "possible" and "potential" are usually confused, conflated and misused.

(1) Historically, there are a number of different "schools" of philosophy which developed over the centuries which often came to different and contradictory philosophical conclusions about reality. Each "school" defined "being" differently, and therefore each defined a human being differently. If one defines a human being differently, then the ethics are defined differently.5 We are all heirs of this legacy - no matter what our academic "field" is.6

a) For example, some realists (e.g., Aristotle, Aquinas) argue that an existing human being is composed of only one complex substance possessing several integrated powers (e.g. vegetative, sensitive and rational) which could not be separated from each other (and therefore no "vegetative", "sensitive" or "rational" powers existing separately on their own). The "soul" is not a separate substance on its own - i.e., a thing in itself - but an integrated power of a concrete embodied human being. There is no real distinction made between a human being and a human person - they are synonymous.7 These schools would (or should) require that "personhood" begins at fertilization, i.e., when the "23" chromosomes of the sperm and the "23" chromosomes of the egg have combined to form the human zygote possessing "46" chromosomes. At this point substantial change has taken place (a change in natures). Embryogenesis, on the other hand, would be understood as only accidental change (only a change in accidents, e.g. size, weight, color, etc.).

b) Some schools (e.g., Plato, many scholastics and Descartes)8 argue that a human being is defined as at least two substances - e.g. soul (or mind), and body - existing independently of each other. The major chronic theoretical problem with these dualistic definitions is that there can be no interaction explainable between these two separate substances. Consequently, these dualistic definitions of a human being were generally rejected often by the very philosophers who proposed them. These schools would have to argue for "delayed" personhood, often explaining embryogenesis as a series of substantial changes (changes in natures).

c) Some schools (e.g. rationalists) define a human being in terms of only one of the two above substances - e.g., Reason (or mind). One major problem with this definition is the exclusion of the other powers of the soul, as well as the matter or the body of a human being. Again, "delayed" personhood is usually argued when "rational attributes" (e.g., self-consciousness, relating with the environment, autonomy, etc.) are passively, or actively, present.

d) Finally, some schools (e.g. empiricists) define a human being in terms of only one of the two above substances - e.g., Body or matter. Again, this definition excludes Reason or Mind from the definition, or somehow equates them. For them, "delayed" personhood is usually present when "sentience" (the ability to feel pain or pleasure - a utilitarian criteria), or brain integration, are passively or actively present.

As will become apparent, the definition of all of those who define a human being or a human person according to "b", "c" or "d" above will contain problematic mind/body split philosophical presuppositions, and eventually would force them to argue for infanticide (indeed, many actually do). The question is: which definition of a "human being" or "human person" most closely matches the correct and accepted scientific evidence and our common experience of human beings?

(2) Often an argument will claim that before a certain embryological marker event there is only a "possible", or only a "potential" human being, or human person, present. That is, a real human being, or human person, does not yet exist but may or could sometime in the future. For example, some claim that a sperm or an egg, or an embryo or fetus, is a "potential person" or a "possible person". Generally this is a corruption of the classical technical philosophical term "potency".9 Properly understood, "potency" refers to a nature or capacity which is already presently existing, rather than, as with "possible" or "potential", something which might or will exist later on. An existing nature or potency itself causes or directs its own species-specific functions and activities.

III. The Contradictory Science Used in the Arguments

Against this rather rough background of the philosophical components embedded in the "personhood" arguments, the following scientific evidence is claimed in support of the various biological marker events of delayed fetal "personhood".

1. The 2-cell stage (first cell cleavage)

- Pro:

Some argue that fertilization is a "process", and therefore there can be no "individual" present; or that the early human embryo is only a "blob", a lump of the mother's tissues, and not a human being. Suarez10 claims that a human person must first be a human being, and a human being begins no later than the completion of the first cell division, with the completion of the genetic input of the program "man". This 2-cell stage is already the same living being as the human adult arising from it. Before the 2-cell stage there is only a "potential person".

- Con:

2. About 5-6 days (implantation)

- Pro:

Bedate and Cefalo15 argue against fertilization because the zygote is not specifically human and does not contain "information" about differentiation. It only contains enough genetic information to proceed through the blastocyst stage. Therefore the human zygote is only a "potential human being", and a "potential human person".

- Con:

As stated above, the human zygote does contain all of the genetic information for all of the processes of embryogenesis, including differentiation. Thus it already possesses its human potency to direct all of its human functions, activities and development.

- Pro:

Differentiation and the other processes of embryogenesis depend on molecular information from the mother, "information" which is not present in the zygote. Therefore the zygote is only a "potential human being".

- Con:

Considerable scientific evidence has already been noted above which demonstrates that specifically human enzymes and proteins are produced after fertilization. And it has also been demonstrated scientifically, precisely, that differentiation is caused by the genetic information in the developing embryo and not by the mother.16 Even molecular information arising within the embryo is determined ultimately by the genetic information in the one-cell zygote ("genetic information cascade"17). Also, molecular information from the mother is only selectively used by the embryo. Such molecular information does not change the very nature of the developing organism. That nature is determined by the presence of "46" chromosomes continuously empirically observable from the zygote through the adult stage. Thus the human zygote is already an existing functioning human being.

- Pro:

The developing embryo can give rise to biological entities which are not human beings, e.g., hydatidiform moles and teratomas. Therefore the human zygote is not a human being yet - only a "potential human being".

- Con:

Hydatidiform moles and teratomas do not arise from genetically normal embryos,18 but from abnormal entities (usually caused by dispermy or parthenogenic eggs; parthenogenesis in humans has never been reported19) which are not, therefore, genetically normal human beings to begin with. Agreed that these entities are not even "possible human beings", much less "potential human beings".

3. About 14-days (individuality, and the formation of the primitive streak)

- Pro:

McCormick and Grobstein20 claim the human zygote has the "theoretic potential" to become an adult - but this potential is "theoretical and statistical", because relatively few actually achieve this in the natural process. "Personhood" (ensoulment) cannot take place until about 14 days. Before then there is only a genetic individual (a "potential person"), or a "pre-embryo"; after, there is also a developmental individual - i.e., a human person. The science used to support these claims include the following.

- Pro:

After fertilization the human zygote undergoes equal divisions, and after the third division the aggregate contains 8 cells "loosely connected". These cells are totipotent, i.e., if separated from the other cells, one of these can produce a complete adult human being. These totipotent cells "do not yet know how many individuals to be yet". They are not, therefore, developmentally single - and therefore, not a person.

- Con:

a) There is no such thing as a "pre-embryo". The term has absolutely no scientific validity, and has been specifically rejected by many deans of human embryology in their well-respected human embryology text books. This scientifically incorrect term can not then be used to scientifically validate any moral status whatsoever.21

b) The cells do not divide equally, but unequally,22 i.e., the zygote divides into 2 cells; then one of those cells divides (giving 3 cells); then the other cell divides (giving 4 cells); then each of these cells divides giving 8 cells. The three-cell stage is significant because we can empirically observe the process of methylation23 (genetic information is turned on or off) for the first time. Methylation patterns - like chromosome patterns - are also coded in the one-cell zygote, and are specific and unique for each individual human zygote.

c) Their depiction of totipotency is very simplistic, e.g., not all of the cells have the same potential as each other or as the original zygote. And totipotency is normal, natural, and determined to happen by the genetic information in the human zygote. These cells are totipotent because certain genes have not yet been silenced by methylation (and other processes) - not because of the reverse claim, i.e, that the genetic determinacy is not yet present, or because the cells "don't know how many individuals to be yet". It knows exactly what it is doing. These cells, in fact, are the most specialized cells, in the sense that they can use far more information than any of those that follow them.

d) The misuse of the term "potential person" has been addressed. "Statistical personhood" is also a misnomer. The "chances" of an embryo coming to term at birth do not change the nature of the human being who is already there. Many fail to distinguish between internal natures and external circumstances which might preclude the already existing nature from continuing its development. The nature is already there, as empirically observed by the number of chromosomes present - even if it does not survive.

- Pro:

Before 14 days there is only a "pre-embryo" (a non-person). For example, at the 5-6 day stage, development does not primarily involve formation of the embryo and its parts [i.e., the inner embryoblast layer of cells] but the "non-embryonic" trophoblast [i.e., the outer layer of cells]. After birth, all of the cells from the trophoblast layer are discarded as the placenta, etc. Therefore, the presence of this non-essential trophoblast layer of cells indicates that the 5-6 day "pre-embryo" is not yet developmentally single, and therefore it is not a person. It is only a "genetic" individual, i.e., a "pre-embryo".

- Con:

The cells of the trophoblast layer [chorion, amnion, yolk sac and allantois] are not "non-embryonic"; and all of these cells are not discarded after birth. The dorsal part of the yolk sac is incorporated into the later embryo as the primordium of the primitive gut. The allantois is represented in the adult human being as a fibrous cord, the median umbilical ligament, which extends from the apex of the urinary bladder to the umbilicus. The allantois is also involved with early blood formation. The primitive blood cells are derived mainly from the epithelial cells of blood vessels in the yolk sac and the allantois.24 Therefore, the 5-6 day stage is both a "genetic" and a "developmental" individual, as there is physical, genetic and developmental continuity from the zygote through the adult stage.

- Pro:

These early cells "have not decided how many individuals they will be", e.g.:

a) If two eight-cell stages of different parentage are fused, a single adult is produced.

b) Up to the 8-cell stage, the developmental singleness of one person has not yet been established. And until 14 days and the formation of the primitive streak twinning, caused by the division of the inner cell mass, can take place. After 14 days twinning cannot take place and the organism is finally "developmentally" single (and therefore a person).


a) Two eight-cell stages of different parentage do not "fuse". Perhaps they mean "recombination". But recombination is not used in this context; it is associated with the crossing over of the male and female genes during the meiotic division of fertilization itself. A chimera and a mosaic are caused by non-disjunction of the chromosomes - not by either "fusion" or by "recombination". These latter two situations can only arise before the 3-cell stage, not at the 8-cell stage. A mosaic is formed by cells of the same genetic origin, not by different parentages. A chimera can be formed from cells of different parentages, but this takes place at the zygotic stage, not at the 8-cell stage.25

b) Again, their depiction of twinning is very simplistic. Monozygotic twinning can take place after 14-days.26 And factors determining monozygotic twinning are not known. Developmental singleness is determined before the 8-cell stage in the case of dizygotic twinning and some monozygotic twinning. Dizygotic twinning appears to be genetically determined (i.e., from the 1-cell stage), and 30% of all monozygotic twinning takes place at the 2-cell to 8-cell stage (not by division of the inner cell mass which is not even present yet).27

- Pro:

The genetic individual is not a developmental individual until a single body axis (primitive streak) has begun to form, near the end of the second post-fertilization week when implantation is under way.

- Con:

Implantation does not start at the end of the second week post-fertilization, but between 6-14 days. The beginning of the formation of the primitive streak is between 15-19 days and disappears by the end of the fourth week.28

4. 14-days (ensoulment)

- Pro:

Ford29 initially argued for "personhood" (ensoulment) at fertilization. But "in light of the new scientific evidence" he changed his position to 14 days. Before that time there are only "groups of cells", a "potential person", or a "biological individual". Until the blastocyst stage, the cells have not been fully differentiated. Full differentiation is not completed until after the formation of the primitive streak (when no twinning can occur) - about 15 days. At that point there is an "ontological individual" (i.e., a person), and ensoulment can take place.

- Con:

Full differentiation is not completed until early adulthood;30 certainly not by the 14-15 day stage. Totipotency, twinning, potential person, etc. have been addressed.

5. 14-90 days (ensoulment)

Based on much of the above incorrect science, Wallace31 (a scholastic Thomist) wants to update a philosophy of nature (natural science), which would ground a theory of delayed personhood. The argument is difficult to paraphrase in a short space, but basically he argues for a succession of souls (vegetative, sensitive, and finally, rational) during human embryogenesis. Each succession is described as a case of substantial change. His model makes use of many of the above claims, as well as several unique to himself:

- Pro:

Each of the "succeeding souls" can be described in terms of the "mature" nature of the individuals of its species (e.g., a mature plant, animal, then human species). If these descriptions are transferred to his model of human embryogenesis - or delayed personhood - we can consider each of these natures as "transient" natures (beings-on-the-way) which successively evolve until the "rational" nature (or soul) is infused and personhood is attained.

- Con:

There is no such thing as two kinds of natures of one and the same specific kind of thing. That is, there are not both "transient" and "mature" natures of a plant, animal or human being - all one has to do is look at the number of chromosomes present, and see that they are the same. An acorn is genetically an oak - albeit a tiny one. The analogy is invalid. Also, if the "rational" human nature which is infused about 3 months is actually descriptive of a "mature" human nature, is it true, then, that a 3 month fetus is actually a mature human being - and acts and functions as one?

- Pro:

Examples from chemistry provide us with the concept of "transient" natures. First, when Na and Cl combine, they actually change their very natures when they form a compound (and are therefore transient). Second, human embryogenesis is analogous to radioisotope decay, where transient "daughter" isotopes succeed from the "parent" isotope.

- Con:

No chemist could agree that Na and Cl change their very natures when they combine32. There is only the sharing of electrons - not of protons. Also, the isotope analogy is invalid. The "daughter" isotopes do not have the same number of protons as the "parent" isotope - and therefore are really different "species".33 However, the human zygote contains the same number of chromosomes ("46") as the parents and is therefore of the same species.

- Pro:

Delayed "personhood" is required to explain human embryogenesis, because the "rational" soul cannot be infused until the "matter" is appropriately organized - at about 3 months. It is the "rational" soul which makes the organism specifically human and which directs and organizes the matter as human.

- Con:

The matter is "appropriately organized" at fertilization, when we know empirically that there is already a human being with "46" chromosomes.34 Immediately there are specifically human enzymes and proteins produced (not tomato or frog enzymes); all of the information for cleavage, differentiation, implantation, etc. is already present; by 3 months specifically human functions, reactions, tissues and organ formations have already taken place (empirically the formation of cabbages or giraffe tissues and organs has not taken place). There is no biological need for a "rational" soul to be infused to make it something it already is, i.e., specifically human and directing human formations. That work has already been done by something back at the zygote stage. Therefore the very concept of delayed "personhood" is scientifically untenable.

6. About 8 weeks, to birth or early childhood (brain criteria - "rational attributes" or sentience)

- Pro:

Many argue35 that "personhood" is determined by the appearance of the nerve net, cortex, or integration of the brain as a whole, etc. These physical structures are the physiological precondition for the capacity for sentience or "rational attributes"; or they signal the actual exercising of those capacities.

- Con:

a) The advocates for the definition of a human person only in terms of either "rational attributes", or of sentience, are using definitions with very specific philosophical presuppositions: Cartesian, rationalists or empiricists. If "rational attributes" define "personhood", then Cartesians (whose theory contains a mind/body split) cannot connect the immaterial "mind" with the physical substrate of the "brain" - there is no interaction possible.36 In addition to this problem, if rationalists define "personhood" as only "rational attributes", then true self-consciousness, autonomy, etc. is not actually present until early childhood37 (and therefore many actually argue for infanticide). If empiricists define "personhood" as only sentience, then actual complete differentiation and sentience is not complete until years after birth (and they, too, argue for infanticide).38 Finally, the precondition for the "precondition" of "rational attributes" or sentience is the human zygote itself. Therefore all of these arguments are arguments from "potential"39, and are definitionally and empirically untenable.

b) The scientific evidence for these claims is empirically vague, scientifically controversial, and only "posited" as theories. Many scientists criticize that there is a reading into the scientific evidence more than is physiologically or conceptually possible. E.g., Jones40 argues that there is no scientific evidence which demonstrates the correlation of "consciousness" and the organizing of the nervous system. There is no valid parallel between "brain death" and "brain birth". "Brain death" is the gradual or rapid cessation of the functions of a brain; "brain birth" is the very gradual acquisition of a function of a developing neural system (which is not a brain). There are no neurological reasons for concluding that an incapacity for consciousness becomes a capacity for consciousness once this point is past. The nervous system of the 8-week fetus is quite different from that of the 8 month fetus or 2 year old child. Thus it is impossible to recognize a distinct point of transition from a "non-brain" to a "brain", or from a non-functioning nervous system to a functioning one. Therefore, Jones concludes, it is impossible to recognize a distinct point of transition from a "non-person" to a "person".

IV. Conclusion

These scientific and philosophical inaccuracies and uncertainties cast a serious doubt as to the integrity of the arguments for "delayed embryo or fetal personhood". On the other hand, the corrected science and a realistic philosophy argue much more coherently for "personhood" at fertilization. A great deal is at stake - especially considering the extent to which the pivotal issue of "personhood" grounds many other related issues in bioethics - specifically, the moral status of the early human embryo used in medical and basic research. Many of those related issues also rely on the correct definition of a "human being" or "human person". If a human being is not also simultaneously a human person from fertilization on, then not only could the infanticide (already argued in the literature) of normal human infants and young children be morally and legally permissible; many adult human populations who are not displaying "rational attributes" will not be "persons", and therefore not entitled to many benefits and protections (e.g., Alzheimer's and Parkinson's patients, patients with multiple sclerosis, the mentally ill and mentally retarded, the depressed elderly, alcoholics, drug addicts, the comatose, paraplegics, the paralyzed, etc.). Thus the conclusions about "personhood" already set in place in the abortion and human embryo research debates are not isolated consideration; those redefinitions could be transferred41 to many other child and adult human populations, as well as to many seemingly unrelated bioethics and public policy issues. This is why it is critical that these inaccuracies and redefinitions in the "personhood" arguments used in the abortion and human embryo research debates should be readdressed and corrected in the literature by genuine experts in these fields.

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