(Linacre Quarterly February 1993, 60:1:18-46 [Updated and extensively revised, September 20, 1996])

Scientific and Philosophical Expertise
an evaluation of the arguments on "Personhood"

Dianne N. Irving, M.A., Ph.D.
Copyright: September 20, 1996
Linacre Quarterly
February 1993, 60:1:18-46
[Updated and extensively revised,
September 20, 1996]
Reproduced with Permission

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I. Introduction

All too often lately we hear or read the lament, "We just don't or can't know what a human being or a human person really is", or, "There just is no consensus or agreement on what the definition of a "human being" or a "human person" is, so why should one person's or one group's definition be preferred over any other. The definition of a "human being" or of a "human person" just cannot be objectively determined, and so must remain a relative one."

The aim of this paper is to debunk these current myths concerning the relativism of what a human being or a human person is, and to at least raise the question at the end of how these "myths" came about even at the level of scientific and philosophical professional "expertise". What I will argue is that we can and do have an objective and empirically-based definition of a human being and a human person, and that, other than conceptually, one cannot really split a human being from a human person. "Personhood" begins when the human being begins - at fertilization.

Toward this end I will address some of the kinds of major scientific and philosophical arguments used to support the sudden appearance of "personhood" at different biological "marker events", indicating that such arguments are arbitrarily grounded on scientific data which is incorrect or misapplied; and that the philosophical claims of these arguments are arbitrarily grounded in systems of philosophy which are themselves very problematic, as any historian of philosophy well knows,1  with highly indefensible definitions of a "human being" or of a "human person". Such definitions are actually remnants of those philosophical systems in which conceptual mind/body splits are still sustained, even today. It is important to understand that the question of "personhood" is not simply restricted to some wild-eyed academic's preferred theoretical ramblings, but that the issue has now been translated into the quite practical question of whether or not these "tiny" human beings are as protected ethically, socially and legally as are more "mature" human beings. The really "burning" question is: if the early human embryo is a human being, is it also a human person?

II. General scientific and philosophical background of the issues

Before addressing the specifics of the science and philosophy, some general charts are provided for an over-all view of the issues. Only a few of the major marker events will be covered, as the actual list is quite long. I refer you, however, to my own analysis of 26 arguments which goes into much greater detail.

Fig. 1 indicates some of the suggested biological marker events during embryological development - from just before fertilization to about 14-days.2  During this period the major philosophical issues include whether the early human embryo is an individual (a prerequisite for personhood), and/or if he/she actually possesses the genetic or formal capacity of a human being or human person. It is during this period also when mass-confusion reigns on the philosophical misuse of the terms "possibility", "probability", "potentiality" and "potency". These positions are generally arguing for either the actual capacity for, or the actual exercising of either "rational attributes" or "sentience".

Daly3  represents the type of argument which claims that "personhood" begins at the time when the sperm has penetrated the ovum. Examples of positions arguing for "fertilization" are my own, or Ashley and O'Rourke4  (although within the advocates of "fertilization", much ambiguity exists as to which point during the process of fertilization itself "personhood" begins). Suarez5  will argue for the 2-cell stage. And a great deal of the current literature consists of arguments for the 14-day stage.6  In these latter arguments a general distinction can be made between those which contain elements concerning the pre-condition for the exercising of so-called "rational attributes" - e.g., self-awareness, self-consciousness, interaction with the environment, etc. - and those concerning the pre-condition for sentience, or the ability to feel pain or pleasure. For those unfamiliar with philosophy, let me just point out that such distinctions - as well as those that will follow - are grounded in different philosophical schools of thought.

Some of the suggested biological marker events range from 14-days and after, as indicated in Fig. 2.7  During this period the major philosophical issues include: individuality, the biological substrate as the precondition for the capacity for "rational attributes", or for "sentience" - or for the actual exercising of those capacities. The full integration of those substrates and capacities are also at issue.

As noted, writers such as Bole8  argue that individuality and ensoulment are not possible until after 2-6 weeks, whereas Singer and Wells9  argue that only after 6 weeks is sentience possible. At 8 weeks Lockwood10  argues for the beginning of "personal identity", and Shea11  for that point where the brain actually controls bodily functions as a whole. Finally, there are those who focus not on the mere capacity but the actual integration and exercising of "rational attributes" and/or sentience as a condition for true personhood, such as Hare12  , Engelhardt13  or Singer14  .

As these and similar distinctions made between a human being and a human person are really philosophical distinctions, I have sketched the major historical philosophical sources of a mind/body split in Fig. 3 (although one could go back to Plato and beyond).15  The major point I want to indicate is that some philosophical schools of thought define a human being as one whole substance, and thus there is no mind/body split inherent in their theories. Such theories define a human being in terms of the actual nature of the human substance. Characteristics such as "rational attributes", sentience, moral autonomy, etc., are only activities of powers which are of secondary consideration, because they are consequent to or follow upon the actual nature of that substance.16  Other "schools" do maintain a mind/body split inherent in their theories; a human being is defined as two independent and separate substances. Interestingly, most of the theories addressed here are derivative of these modern philosophies, especially that of Descartes.17 

An entire paper - or even a book - could be dedicated to explaining the theoretical and practical consequences of such mind/body splits, especially in the present context. Suffice it to point out that where there is such a split - where the mind (or even the whole "soul") is an independent substance in and of itself, separate or apart from the "body" (which is seen as an independent and separate substance in and of itself), then it is impossible either theoretically or biologically to "piece them back together again", as Humpty Dumpty might have said. Nor could one explain any interaction between these separate "substances" of mind and body. We can see the effect of such Cartesian dualism - and the consequent historical breaking-off to either rationalism or empiricism - in the distinctions writers make here between a human being and a human person.

III. Biological marker events of personhood

There are enumerable points along the continuum of embryological development at which different writers claim the appearance of so-called "personhood". These are claimed as "biological marker events of personhood" - before which there is only a human being (at best); and after which there is a human person. Before that biological point, then, the human embryo or human fetus is considered as only an "object", a "thing" which may be used or dealt with according to the personal objectives or desires of a human person. After that particular biological marker event we suddenly have a human person, who is now considered a "subject" or an entity deserving of protections against the interests, objectives or desires of another human person.

A. Fertilization as the beginning of personhood

In order to identify the major issue quickly, a few questions might be posed so as to clarify at the start exactly what is at stake when we define a human being or a human person in one way or another. If our definition is incorrect - even in part - then the consequences of this incorrect definition are long-ranged and potentially profound. Aristotle reminds us of something we all know too well. To paraphrase him: a small error in the beginning leads to a multitude of errors in the end.18  In this case, if one's definition of a human person is incorrect, then one might find one's self experimenting on or euthanizing something which one thought was not a human being or a human person - but which in fact really is.

So I pose the question - how would you yourself define a human person? Would you consider any of the following a human person: a rock; a head of cabbage; a giraffe; …those who are old and senile in a nursing home; Alzheimer's patients; Parkinsonian patients; stroke victims; comatose patients; drunks and alcoholics; drug addicts; the homeless, poor; prisoners; the emotionally ill and depressed; mothers-in-law; teenagers; the physically handicapped; the mentally ill; children under 7 years of age; a new-born baby; the fetus before the mother has given birth (or, at 6 months, 8 weeks, 35 days, 14 days, 6 days, 2 days, fertilization, or the egg or the sperm). These latter examples actually constitute some of the different biological markers at which various writers variously claim that there is present a human person. Obviously there is some disagreement about exactly when we have, definitionally, a human person present. And that period of time between fertilization and 14 days is the grayest area, i.e., the seemingly most difficult and most controversial stage.

What, then is a human being or person - and when does he or she begin? I will argue that at the biological marker of fertilization a substantial change (or a change in natures) has taken place - and a new, unique, living, individual embryonic human being who is simultaneously a human person is present. I will also argue that from fertilization onward - including the zero to 14-day old embryonic human stage - until the death of the adult organism - accidental change (or a change only in accidents) has taken place, in which a human being/person is continuously present.19 

1. The connection between science and philosophy

First, although a question about "natures" seems to be fundamentally a philosophical one, I would argue that any philosophical reflections, analyses or accounts about the nature of a human being or person must begin or start with the empirically observable biological facts.20  Otherwise our philosophical concepts actually bear little or no relation or resemblance to the real world which we are trying to understand and explain by those philosophical concepts. Instead, I would suggest, we are left with multiple half-truths or fantasies - or wishful thinking! Epistemologically, the starting point of our philosophical questions and investigations about reality must be grounded in that empirical and scientific reality. Only in this way can we have a realistic or objectively-based definition of a human being - one that is not relativistic.

Operationally, what is the connection between a thing's nature and the biological facts? Put briefly, the answer is that we can know what a thing is (i.e., its nature) by observing its actions and functions - how it behaves, what it does. We know that a thing acts according to the kind of thing it is, i.e., its nature. That is simply an empirically observable fact. In first-year chemistry or in microbiology students are given "unknowns", the nature of which they must identify by means of the kinds of actions or reactions exhibited by these "unknowns" as observed in the lab. Indeed, this is the obvious principle behind any basic or experimental research. The research biologist first observes the actions, reactions, functions of a biological entity and reasons from these specific kinds of actions back to the specific kind of nature it possesses. It is this nature which directs and causes such characteristic actions. As biology texts themselves discuss it: function follows form.21  Thus Na burns orange, and cobalt burns blue/green -or beta-hemolytic streptococcus can only be grown on specific culture medium containing blood, but not on other mediums. Further, a thing is not only characterized by its nature, which determines the specific kinds of actions it can do - but that same nature limits the kinds of actions it can do. That is, there are certain actions which a thing can not do because it does not have the specific kind of nature it would need to do it. For example, birds have wings and so can fly - but stones, dogs or human beings can't fly; corn stalks produce ears of corn and corn proteins and corn enzymes - but acorns, tomato plants or asteroids do not and cannot produce corn or corn proteins. Frog embryos direct the formation of frog tissues and organs -but they cannot direct the formation of human tissues and organs.

Apply these considerations to the point at hand. To determine what a human being or person is is really not all so difficult as is often claimed. We are not Gods or angels - but embodied human beings.22   We do have bodies - don't we? At least I have never seen a simple "soul" wandering aimlessly around the labs, manipulating a computer, cooking dinner or playing soccer without a body. In fact, I have never seen even a Platonic or a Cartesian philosopher "thinking" without his or her body! As Aristotle noted, the whole man thinks; the whole man knows; and the whole man acts.23  There are voluminous biological facts which we do know already about the human body and its embryological development. Clearly by observing and studying these known biological facts - how the human being begins his or her biological existence as a specifically human zygote, and the kinds of specifically human functions and human actions that take place during embryological development - we can then determine to a very sophisticated extent the nature of a human being or a human embryo - or "what" it is. So I will turn now to a brief consideration of the well-known, well-referenced biological facts concerning when the life of a human being begins to exist and how it then merely grows and develops during embryogenesis, without changing "natures".

2. The scientific facts

Before fertilization there exist a human sperm (containing 23 chromosomes) and a human ovum (also containing 23 chromosomes - the same number, but different kinds of chromosomes).24  Neither the sperm nor the ovum, singly, by itself, can become a human being - even if implanted in the womb of the mother. They are only gametes - they are not human embryos or human beings. In contrast, the single-cell embryonic human zygote formed after fertilization (the beginning of the human being and the embryonic period)25  contains 46 chromosomes (the number of chromosomes which is specific for members of the human species) - and these 46 chromosomes are mixed differently from the 46 chromosomes as found in either the mother or the father - that is, they are unique for that human individual. And at the single-cell embryonic human zygote stage that unique individual human being is already genetically a girl or a boy.26  If allowed to "do his or her own thing", so to speak, this embryonic human zygote will biologically develop continuously without any biological interruptions, or gaps, throughout the embryonic, fetal, neo-natal, childhood and adulthood stages - until the death of the organism. And with the advent of in vitro fertilization techniques, we can see that the early human embryo can develop in vitro on his or her own without the nutrition or protection of the mother for quite a while - someday, perhaps, even until "birth"!

I want to reiterate that a human gamete is not a human being or a human person. The number of chromosomes is only 23; it only acts or functions biologically as an ovum or as a sperm, e.g, it only makes ovum or sperm enzymes and proteins, etc., not specifically human enzymes and proteins; and by itself it does not have the actual nature or potency yet to develop into a human embryo, fetus, child, or adult. And in that sense gametes are only possible human beings (i.e., human beings who do not exist as yet). Only after the sperm and the ovum chromosomes combine properly and completely do we have a human being. Individually, the nature of a sperm is different from the nature of an ovum - and both are different from the nature of the embryonic human zygote which is formed when their chromosomes combine.

Thus from perhaps an Aristotle-the-biologist's point of view, one would say that before fertilization there are two natures - i.e., the nature of an ovum and the nature of a sperm. After fertilization there is a human zygote with one nature, i.e., the nature of a human being. Thus, in fertilization there is substantial change,27  (i.e., a change in substance or nature - or "what" it is). The substances or natures of the ovum and the sperm have changed into the nature of a human being. This is, in fact, known empirically by observing the number and kinds of chromosomes present before and after fertilization, and by empirically observing the different characteristically specific actions and functions of the ovum, the sperm, and the human zygote. Once fertilization has taken place and the new human being has formed, only accidental change28  occurs (e.g., a change in weight, height, size, shape, etc.), and we know this empirically as well. We can observe that the nature of the human being does not change (e.g., into a cabbage or a giraffe), only its human accidents change.

Thus embryological development does not entail substantial change, but only accidental change. Once it is a human being it stays a human being, and acts and functions biologically as a human being. The human zygote produces specifically human enzymes and proteins; he or she forms specifically human tissues and organ systems, and develops humanly continuously from the stage of a single-cell human zygotic embryo to the stage of a human adult.29 

This is observed empirically. A human zygote does not produce cabbage or carrot enzymes or proteins, and does not develop into a rock, an ear of corn, nor into a cat, a horse, a chicken, or a giraffe. Empirically it is observed that a human zygote produces specifically and characteristically human proteins and enzymes at the moment of fertilization - as demonstrated recently, for example, by experiments using transgenic mice30  - and that he or she develops continuously throughout embryological development in a specifically and characteristically human way.

In short - the biological facts demonstrate that at fertilization we have a real human being with a truly human nature. It is not that he or she will become a human being - he or she already is a human being. We know that empirically. And this nature or capacity to act in a certain characteristic way is called, philosophically, a nature or a potency.31  Thus a human zygote or embryo is not a possible human being;32  nor is he or she a potential human being;33  he or she is already a human being. A human zygote, embryo or fetus does not have the potency to become a human being, but already possesses the nature or capacity to be at that moment a human being. And that nature will direct the accidental development, i.e., the embryological development, of his or her own self from the most immature stage of a human being to the most mature stage of a human being.

Now, this is strongly convincing empirical evidence that at fertilization there is present a human being (the well-referenced unequivocally agreed upon answer to the scientific question); but is there also a human person (a philosophical question) - or not? These are two different questions - one scientific, the other philosophical. It is in this shifting from the paradigm of a human being to that of a human person where the philosophy - and the confusion - come into play. Is a human being also a human person; or are they different things? Which philosophy is adequate to cope with this biological data?

3. The matching philosophical concepts

(Fig. 3) With even only a cursory rummaging through the history of philosophy, there is one major "realistic" philosophical "ball-park" which would in fact deny that there was any real (as opposed to conceptual) essential distinction between a human being and a human person. That is, in the real world which we experience empirically, they cannot really be split or separated - except perhaps only conceptually. This philosophy was part of a 2500 year old tradition which was the bath water, so to speak, that was "thrown out with the baby". It is the philosophical ball-park, for example, of Aristotle-the-biologist.34  For Aristotle - as well as for others, such as Thomas Aquinas - his major metaphysical and anthropological treatises argue consistently for a single human substance with no mind/body split (although there is evidence of a serious Platonic streak in his De Anima - that atypical and historically problematic treatise of Aristotle's so often quoted by contemporary scholars - as well as historians who researched for Roe v Wade). As Aristotle argues, "…'nature' has two senses - matter and form. If one considers 'nature' as the form, then it would be the shape or form (not separate except in statement) of things which have in themselves a source of motion"35  (emphasis added). Again, he says, …"the physicist is concerned only with things whose forms are separable [in the mind], indeed, but do not exist apart from matter."36  And similarly, matter cannot exist apart from the form. For Aristotle, the human being is defined as one composite substance - the vegetative, sensitive and rational powers of the "soul" together with the human "body".37  The whole soul, he wrote, is homogenous, and in each part of the body as one whole composite:

In each of the bodily parts there are present all the parts of the soul, and the souls so present are homogenous with one another and with the whole; this means that the several parts of the soul are indisseverable from one another.38  (emphasis added)

And in contrast to his opposite view in the very same De Anima, Aristotle addresses the very possibility of a "being-on-the-way", or an "intermediate" human being, railing against the anthropological consequences of Plato's or Pythagoras' mind/body split when he very sarcastically retorts: "Yet how are we to believe in such things?" (emphasis in the original).39  Although Aristotle-proper did not actually use the term "person", he clearly would have to concur that a human being is always a human person, for neither form nor matter can exist on their own as two different things or independent substances.

Thomas Aquinas, to give another example, puts an even finer gloss on Aristotle's anthropology, by affirming his own adamant rejection of Plato's anthropology. To paraphrase Thomas: the name of "person" (and he uses that term) does not belong to the rational part of the soul, nor to the whole soul alone - but to the entire human substance (or, subsistens).40  This means that the whole soul, whole body and its act of existing constitute one substance entire - with no separate and troublesome independent "parts" each of which are claimed to be true and independent whole substances. And it is worth noting that Aquinas is one of the only philosophers who includes undesignated matter in his formal definitions of natural things - of which man is one.41 

For Thomas a human being is a human person, and the later characteristics which we will look at in these debates, such as "rational attributes", autonomous willing or sentience, are only consequential and secondary or accidental actions which follow upon certain powers (not "parts") which themselves follow upon the essential nature of the human being itself.42  That nature is defined as the single, whole, formal, material and existential human substance. As Thomas states:

…the soul must be in the whole body [and therefore not just in the brain], and in each part thereof …for to the nature of the species belongs what the definition signifies; and in natural things, the definition does not signify the form only, but the form and the matter…so it belongs to the notion of man [definition] to be composed of soul, flesh and bones.43  (emphasis added)

These philosophical precisions force at least two major questions on any of the several types of Aristotlean/Thomistic frameworks used in these debates. First, if it is claimed that the "rational" soul - which "organizes and directs embryological development" - is not infused until about the third month,44  then what explains the specifically human organization of the human embryo and human fetus up to that point? Hasn't the work of this supposed "delayed rational soul" already been done - as empirically verified? If so, then this biological evidence of specifically human organization which we do empirically observe must be accounted for by the presence of the human soul right from the beginning. In addition to the specifically human structural organization from the beginning, we also empirically observe specifically human functions and activities from the beginning - e.g., the production of specifically human proteins, enzymes, etc. If so, then this biological evidence of specifically human functions and activities which we do empirically observe must be accounted for by the presence of the human soul right from the beginning.

Second, for both Aristotle and Thomas the "rational soul", or more properly, power, includes virtually the vegetative and sensitive powers,45  and for neither is there such a thing as a "rational soul" alone, or even a whole soul alone - or a whole soul without a body (except in some sections of the De Anima). The whole existing human complex (body and soul - and for Thomas, esse) must be present together at once.

Apart from the biological and conceptual absurdity of an "intermediate man" walking down the street, if there were only a "vegetative" soul present at first, how do we explain the production of specifically human enzymes and proteins - instead of carrot or corn enzymes - from the very start? If there were only a "vegetative and sensitive" soul present, how do we explain the production of specifically human tissue and organs - instead of only giraffe or gorilla organs and systems? If the human soul cannot be split (and must contain all three powers at once), and if specifically human enzymes, proteins, tissues, organs and structures are empirically observed - which they are - then the human rational soul must be present at the very beginning along with the human vegetative and sensitive "powers" (not "parts") of the human soul. And this "soul" - or, more properly, these powers - must exist as a composite with the human body which it is organizing and whose functions and activities it is directing from the moment of fertilization - which we know empirically.

Thus, at fertilization, I would argue, the "matter" (i.e., the newly combined fertilized ovum or embryonic single-cell zygote) is already appropriately organized as human - since we empirically observe it as specifically human and as developing humanly from the beginning.46 

So far the scientific facts and the philosophical concepts match. At this point I want to take a closer look at the biological facts after fertilization, i.e., those of human embryological growth and development. Along the way I will point out several other different biological "marker events" of personhood which have been variously argued by others. All of these writers will make a real distinction between a human being and a human person - supposedly based on these biological marker events. The use of certain biological data which they will use to support their arguments will also be addressed. (The use of their problematic philosophies with mind/body splits, which seem to be imposed upon their problematic biological facts, will be discussed later in this paper).

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