On the Personhood of Pre-implantation Embryos
(A Warning That the Pro-life Community Is Largely Going Too Far)


It hardly needs to be argued that the fundamental issue at the crux of the abortion debate is the question of when personhood begins. This is self-evident. Abortion would be quite simply unthinkable if the fetus was viewed as an individual human person, rather than simply as a mass of living human cells which happens to be a potential person.

The pro-life community in America, while not entirely monolithic even in this area, has nonetheless been dominated by a surprisingly united political and moral conviction on this question. By and large, they argue that human life and personhood begin at the moment of conception, which they almost universally define as fertilization.[1] Understandably, therefore, they have loudly decried as immoral all practices that involve the destruction of fertilized human eggs and resulting embryos, no matter how early in development. These practices include embryonic stem cell research, in vitro fertilization, and methods of birth control that allow fertilization but prevent the embryo from implanting in the uterus, such as IUDs and sometimes even hormonal birth control methods (including “the pill”), which many argue could theoretically do the same thing.

The argument that personhood begins at fertilization is not usually presented as a Biblical or religious argument, but rather as a scientific argument.[2] Furthermore, it is usually presented not as a debatable point or something on which further research may shed more light, but rather as something that is quite firmly established. The following quote is a typical example:

[It is] a scientific, indisputable fact that we have known [from] well before Roe v. Wade, that human life begins at fertilization, when a father’s sperm and mother’s egg unite. After that point, the being is a growing, maturing human person. After fertilization, nothing makes us any more alive or any more human than the moment before.[3]

The fundamental claim made by this statement is heartily reiterated and insisted upon by most people in the pro-life movement, as politicians seeking their endorsement are very well aware. But is the claim really true? Is it really an indisputable scientific fact that from the moment of fertilization an embryo is a “growing, maturing human person?” I am concerned that the majority of Christians and others who oppose abortion seem to have simply accepted and propagated this dogma as unquestionable truth without ever really seeing any need to honestly consider the evidence for or against it.

Of course, one of the reasons for our reluctance to truly investigate this issue is that most of us have absolutely no training or expertise in this field. I include myself in this statement. I am a complete amateur, and not a very knowledgeable one at that. But it seems to me that even a cursory investigation into this issue actually uncovers some fairly simple, common-sense evidence that ought to be thoughtfully considered. In this paper I will attempt to present this evidence as plainly as possible to show why, even though I am pro-life, I do not accept the claim that human embryos in the pre-implantation stage must logically be viewed as persons.

Preliminary Discussion: Personhood and Life

The terms personhood and human life are sometimes used interchangeably, and this can be a source of contention, so it is good to begin with a more careful consideration of their relationship. Clearly, in the context of this issue, when we speak of human life we mean more than simply biological life that is human in character or origin. Rather, human life must be defined in terms of human beings or individuals. For example, human blood contains cells that are alive and human in character, but no one would argue that blood cells are individual human beings. However, a newborn infant is not just human in character, he or she is an individual human being.

The relationship of human life to personhood is not quite so straightforward, however. In fact, strictly speaking, the issue of personhood cannot be addressed scientifically at all. This is because personhood is not a scientific concept, but rather a theological (or at least philosophical) concept. Personhood in the eyes of God is what matters. Theologically, we could probably equate it to the existence of an immaterial soul. But the fact that the soul is by definition immaterial clearly places it out of the bounds of scientific discovery.

Normally, of course, this is not of much practical consequence, because personhood clearly goes hand-in-hand with human life most of the time. But the question of whether personhood is therefore directly and inviolably connected with human life actually is a true difficulty, as the advent of modern medicine sometimes brings starkly to our attention. For example, there are cases where an individual human body can be kept “alive” on machines even after many (both Christian and non-Christian) would argue that the “person” has actually died, generally due to the cessation of cognitive brain activity, while others would argue that as long as the body is alive, so is the person. This is not a simple dilemma!

In fact, because this task of technically defining the relationship and distinction between personhood and human life is so extremely difficult, I frankly do not even propose to attempt it. As it pertains to the issue of abortion and the beginning of personhood, I suggest rather that a cautious practical approach is in order. In other words, even though it is possible that personhood in the eyes of God might not technically begin until sometime distinctly after individual human life begins (possibly at the onset of cognitive brain activity, for example), I do not see any way for us to be able to know that with certainty. Therefore, I believe the most ethical and reasonable path is to treat the beginning of individual human life as the beginning of personhood, rather than risk the abortion of lives that might indeed possibly be real persons. So in practice, for the purposes of the subject of this paper, the core question of when personhood begins really boils down to the question of when individual human life begins, even though in absolute terms this might not actually be the case.

This practical equation of personhood to human life is often reflected in everyday language, as I have already noted. Many on both sides of the abortion debate simply use the term “human life” to mean personhood, without explicitly defining any distinction. But regardless of which phraseology we adopt, the approach suggested above still applies. The core practical question still boils down to when is the earliest an individual human life might begin. It is a matter of exercising reasonable and proper caution, realizing that the destruction of actual living persons is potentially involved. U.S. President Ronald Reagan elucidated this concern quite eloquently as follows:

Anyone who doesn’t feel sure whether we are talking about a second human life should clearly give life the benefit of the doubt. If you don’t know whether a body is alive or dead, you would never bury it. I think this consideration itself should be enough for all of us to insist on protecting the unborn.[4]

With this preliminary approach established, we must now turn to the investigation of what insights modern science can offer on this question of when is the earliest individual human life can reasonably be considered to begin.

Deficiency of the Genetic Argument

It is not difficult to understand why so many in the pro-life community regard fertilization as the firmly established scientific beginning of individual human life. The main reason is what I will call the genetic argument. Normally, one of the clearest scientific ways to distinguish one human life from another is by the genetic “fingerprint” of every living being. Crime scene investigators can tell which person a cell came from by investigating the DNA from that cell and comparing it to each suspect. Therefore, since fertilization results in a new DNA sequence being created, it is natural to think of the fertilized egg as being the formation of a new individual human person or life.

As natural as this line of thinking might seem, there are some real problems with its core premise that human individuality (or individual human life) is somehow tied to genetic sequence. Almost everyone is aware that having a unique genetic sequence is not a necessary condition for being a unique individual, since identical twins share the same genetic sequence. But the typical pro-life argument is that even though it is admittedly not a necessary condition for being a unique individual, it is still a sufficient condition. However, even this weakened form of the argument is not technically true. For example, in the process of normal body growth, cells sometimes mutate as they replicate, resulting in cells that do not share an identical genetic sequence with other cells in the same person. These mutated cells are often non-functional and are cleared out of the body by the immune system. Sometimes they are downright dangerous and manifest themselves as a growing cancer in the body. But other times they can simply be benign, existing as part of the body even though their genetic sequence is unique. Surely no one would think of these cells as belonging to a different individual human being than the body they are a part of, simply because they have a different genetic sequence.

There is, of course, an extremely large quantitative difference between this phenomenon and the phenomenon of a new genetic sequence that occurs at fertilization. In one case, only one or a few base pairs of the DNA are changed, whereas in the other it is a vast number. But the point remains that this is a quantitative difference rather than a qualitative difference, which goes to show that the presence of a new, unique genetic sequence does not in and of itself necessitate a distinct human being.

Another way to see the difficulty with the core assumption of the genetic argument is by conducting a little thought experiment. The human genome has already been sequenced, meaning essentially that the complete genetic code of several real persons is now available in computerized form. Theoretically, genetic engineers could manipulate this data to represent new human genome sequences, playing around with different combinations of genes, etc. Obviously, a mere database containing this new genetic sequence could not be considered a person. But it is not inconceivable that in the near future a DNA molecule could actually be synthesized to match the sequence in such a database. If a unique genetic sequence is a sufficient condition for a unique human being, would this new DNA molecule be considered a person? What if the DNA molecule was implanted in some ordinary type of cell, say a skin cell or a red blood cell? What if it was implanted in an egg cell?

The point in all this is not to pinpoint the actual necessary conditions for considering something with a unique genetic sequence to also be a unique human life, but only to illustrate the fact that this would be very difficult to define. This goes to show that the mere presence of a unique genetic sequence is clearly not a sufficient condition for being an individual human life. Therefore, the fact that a fertilized egg has a unique genetic sequence does not mean that it is necessarily a human being. The genetic argument may suggest the possibility of a distinct human being in this case, but it does not in and of itself offer any convincing proof of that claim. Further considerations must be investigated.

Twinning and Recombination

The processes of identical twinning and recombination form one of the most commonly-raised objections to the typical pro-life argument that an embryo is a unique human being from the moment of fertilization. It is well-known that a human embryo in the pre-implantation stage can divide into two, resulting in identical twins. (Actually this can occur even a few days after implantation, up to approximately the 14th day after fertilization.) Also, this twinning process can be artificially induced, which shows that any embryo at this stage must inherently possess this capability of dividing. This means that twinning cannot be explained as a matter of certain embryos being a combination of two distinct human lives all along, which later separate from one another. So if the embryo is viewed as already being an individual human life before the twinning occurred, the natural question is what happened to that original life?

This question does not in and of itself disprove the theory that individual human life begins at fertilization. The twinning process could certainly be viewed simply as one life giving rise to another in addition to itself, in a similar way to how one life could be cloned in a laboratory. In the case of embryo division, we would be left with the somewhat puzzling question of which of the two twins was the original life, since there is no obvious asymmetry in the process to identify one of the embryos any more closely with the original embryo than the other. But this does not disprove the possibility that one of the lives may in fact be the original. Alternatively, it could be hypothesized that the original individual human life was destroyed but spontaneously gave rise to two different individual human lives.

In fact, many pro-life advocates have argued along these exact lines, and have illustrated their argument by comparing the twinning process to a strange but well-known oddity of a type of flatworm called a planarian. If a planarian is cut into two parts, each of the parts will regenerate the missing portion so that the result is two fully functional individual planaria. Amazingly, this is true even if one of the parts is just a tiny fraction of the original planarian. Also, it is true even if the cut is in halves lengthwise, from head to tail, so that the head does not fully belong to either half, and neither of the resulting planaria can be more closely linked with the original than the other. Yet this certainly does not mean that the original planarian was not a real, individual life, regardless of whether that original life is viewed as being destroyed by the cut and giving rise to two new individual planaria, or whether the original is viewed as living on in one of the two.

However, although this may seem to be a convincing analogy at first glance, if we think it through carefully I do not believe it leads to the conclusion that the pro-life community is advancing at all. In fact, it actually does nothing whatsoever to argue for the two separated parts of the original planarian being themselves individual planarian lives from the moment of the cut, rather than later becoming individuals. Certainly in the case of a very asymmetric cut, with one part only being a small portion of the tail, it would seem far more natural to view the severed tail part as something less than a new individual planaria, at least until it began to regenerate a new body and head. Probably the most convincing argument for this would be if the tail part were to be immediately reattached to the main part, just as doctors can reattach a severed limb to a living human being. I am not aware of any laboratory experiments to confirm if such a reattachment can be performed in the case of a planarian, but the natural assumption would certainly be that it would be possible, at least in theory.

If a part of an individual living being can be reattached to the original being to make the original whole again, it would seem grotesque to assume that the part was actually a different individual life. The fact that the part (in this case the severed tail portion of the planarian) can and will eventually develop into a new individual planarian if it is not reattached does not change this, anymore than the possibility of cloning a human from a severed finger would mean that the severed finger was already an individual human life. What makes the planarian analogy seem so different from the case of a severed limb is the fact that planaria can be split in a completely symmetrical, lengthwise fashion. This case is admittedly a little more speculative as to the details of what might be happening. I would think the natural assumption would be that both halves are like the severed tail portion of the first example. In other words, I would view the original planarian as being destroyed in this case (since the head is split), and the result is two parts that initially are not actual individual living planaria at all, even though both parts will eventually grow into individual living planaria. And if it could be shown that the two halves could be reattached and result in one new individual planarian instead of two, this would certainly be very convincing evidence that the two halves were not already individual planaria, just as in the case of a severed tail which is not really an individual planarian.

This discussion about the possibility of reattaching planaria halves has admittedly been somewhat speculative on my part. I do not know if planaria halves can be recombined. What is very well-known, however, is that embryos that have divided actually can be recombined. As bizarre as it may seem (especially for those who are accustomed to thinking of embryos as individual human beings from the moment of fertilization), the fact is that embryos in the very early stages can actually merge together and develop into a single individual. If the embryos are of different genetic makeup, this phenomenon is called mosaicism and the result is a tetragametic chimera, an individual that carries a mixture of genetically distinct tissues but is otherwise usually very normal. Human chimeras of this kind are rare, but there are documented cases. A more common merging scenario is when an embryo divides into two in the identical twinning process and then later recombines back into one. This is the other half of the twinning and recombination argument against the common pro-life claim that we have been considering, and it seems to me to be very convincing indeed.

The common pro-life theory that a fertilized egg is an individual human even in the stage where it can undergo twinning and recombination is very hard-pressed to explain the implications of the latter phenomenon in a reasonable way. If the two resulting embryos after the process of twinning are viewed merely as parts that have the potential to develop into human beings (comparable to our natural assumption about the nature of planarian parts), then the whole theory is basically disqualified. At the very least it would lead us to question whether the original embryo might not also be more accurately viewed merely as something which has the potential to develop into an individual human, rather than something which already is an individual human. There would not seem to be any scientific reason to view the original embryo as somehow fundamentally different in nature than the two resulting parts, since at this stage the cells in the embryo are completely undifferentiated, and the number of cells does not seem to affect the nature of the embryo. So the theory is forced to insist upon the two embryos resulting from the division as being individual human lives right from the time of the split, no matter how unnatural this might seem. And this means that for the case of the two embryos undergoing a process of recombination, even hypothetically one which occurs immediately after the twinning, the theory has to view this as the death of at least one individual human being, even though the resulting single embryo is in the exact same configuration as the original embryo before the split. This seems to me to be very unlikely, especially in view of the complete lack of evidence for the only theory that demands it. To call such a theory not just an imaginative possibility but actually an indisputable scientific fact simply goes beyond the bounds of reason.

Ethical Implications for Breast-feeding

Beyond the natural scientific argument above for an embryo not being an individual human being until at least after the stage where twinning and recombination is a possibility (sometime after implantation), there is also a convincing ethical argument, at least for people who are reticent to assume breast-feeding mothers may be guilty of destroying human life.

Those who insist that pre-implantation embryos are persons are at least being consistent in their view that this means women should not use IUDs or other birth control methods that may allow fertilization but prevent implantation. However, what many of them fail to realize is that logical consistency would also demand the same caution in the use of breast-feeding, for the same reason. Research has shown that if a woman chooses to breast-feed her baby, which causes the temporary cessation of both ovulation and the normal uterine development necessary for implantation, it is frequently the case that ovulation will resume prior to the ability of the uterus to support implantation.[5] The result is that if the egg is fertilized, it will be aborted. If it is morally wrong to cause the possibility of an egg to be fertilized which cannot also be implanted, then logically it would also be wrong for a woman to breast-feed without also remaining abstinent or using some other form of contraception until the uterine cycle was completely back to normal.

Of course, the fact that breast-feeding can have this effect does not disprove the theory that individual human life begins at fertilization. But it does show that the practical and ethical implications of this theory are perhaps more far-reaching than many of its proponents would be comfortable to admit. Are we really to believe that God designed the human body in such a way that millions of women throughout history have unknowingly killed their babies simply by breast-feeding? Are we really to believe that now that we understand this process better, women now have a new responsibility to either avoid breast-feeding or else take steps to prevent fertilization during this time? This hardly seems likely to me. I think it is far more reasonable to assume that God does not view unimplanted embryos as persons, exactly as the scientific evidence suggests.


I am very well aware that the arguments given in this paper will not sit well with the majority in the pro-life community, so I want to reiterate once again that I am not a traitor to the pro-life cause. I hope I have made myself very clear on this. I have not been arguing for ambivalence or acceptance of the practice of pregnant women getting abortions. I have not been siding with the pro-choice community, which by and large believes that the beginning of personhood is an issue that every woman ought to be completely free to decide for herself. I believe a civilized society ought to have reasonable rules to govern such things, since human lives are at least potentially at stake.

What I have suggested, however, is that the pro-life community has mostly gone too far in their reaction to the pro-choice view. Specifically, they go too far in their rigid insistence that every embryo must be viewed as a human person, even those that are not yet implanted in a woman’s womb. It seems to me that the most sensible conclusion is that there is no scientific reason at all to consider pre-implantation embryos as actual human beings, and therefore the argument that they are persons cannot be considered as a valid objection to such practices as embryonic stem cell research.[6] It is true that these embryos are living, and that they are not really simply a part of the woman’s body, and that they are human in character and origin, but they are not individual humans, and thus I do not see how they could be viewed as corresponding to individual human souls. They are not persons.

I believe my approach has been one of reasonable caution. I have not claimed or even postulated that the personhood of embryos is somehow intrinsically linked to implantation. Rather, I have only observed that they do not seem to meet any rational criteria of personhood in the pre-implantation stage. I have acknowledged the possibility of personhood for embryos at all points beyond this stage, simply because I know of no later stage at which to draw the line with what I would consider to be a solid degree of confidence that human life is not being jeopardized.

Some will no doubt argue that I am not being cautious enough. The arguments that I have given regarding embryos in the pre-implantation stage will not seem strong enough to these people to rule out every last possibility that unimplanted embryos may in fact be real human persons. I understand this concern. I acknowledge that it is possible to hold this view with integrity. That is, I acknowledge that one could argue that in spite of all the difficulties with this view, there still might be a chance that individual human life could possibly begin at fertilization, even though this is not the conclusion I have personally come to. I have no quarrel with these people. But I do not believe it is possible to argue with moral and intellectual integrity that it is an indisputable scientific fact that human life begins at fertilization, and I must simply protest that the pro-life community is going too far when they use this kind of rhetoric.

Update [4/25/2012]: I have also written a short but more rigorously philosophical presentation of these arguments here.


[1]   Note that outside of the pro-life community, the term “conception” is not always quite so unambiguously defined. For example, one common dictionary definition (Merriam Webster’s Tenth Edition) is “the act of becoming pregnant,” which both the American and British Medical Associations regard as occurring at implantation rather than at fertilization. In any case, the fundamental issue of when personhood begins is obviously not dependent on whether the word “conception” is taken to refer to fertilization or implantation.

A more interesting difficulty is that even if conception is defined as fertilization, the definition is still not completely unambiguous. This is because fertilization is a process that takes several hours to complete, so even those who argue that personhood begins at fertilization cannot really pinpoint a precise “moment of conception” when this occurs. For example, does the egg become a person when the sperm cell first penetrates the outer covering of the oocyte, or when the oocyte then changes into a mature ovum by completing the meiosis II process to select a unique chromatid from each of its 23 chromosomes, or when the nuclear membrane of the sperm then disintegrates to allow its chromosomes to enter the cytoplasm of the ovum, or what? Fortunately, as far as I know, none of the real-life issues like stem cell research that are affected by this debate actually involve the destruction of partially fertilized eggs, so in practice it is not (yet) necessary even for those who hold to the view of personhood beginning at fertilization to answer this question precisely.
[2]   This is not to deny that there are passages in the Bible that strongly imply personhood before birth (e.g., Luke 1:15). However, it would be exceedingly difficult to argue that the Bible even speaks at all to the issue of whether personhood actually begins at fertilization rather than at some other time such as implantation or later. For example, it would be a clear case of eisegesis to read the concept of fertilization into verses which refer to conception (e.g., Ps. 51:5). The Hebrew and Greek words for conception simply cannot be pinpointed this precisely, as the process of fertilization was not understood at the time those languages were in use. The idea of conception in the Bible simply refers to the act of becoming pregnant. It is something that happens to the woman (in contrast to fertilization, which happens to the egg), and it happens some amount of time after sexual relations but obviously well before birth (e.g., Gen. 4:1, 16:4, 1 Sam. 1:19-20). Beyond this, no precise time frame can be inferred.
[3]   From an essay by Dr. Patrick Johnston available online at http://www.newswithviews.com/Johnston/patrick19.htm. Dr. Johnston is arguing for a proposed 2008 Colorado constitutional amendment that would define personhood as beginning at fertilization. I have heard other leading supporters of this amendment (spearheaded by the Colorado for Equal Rights organization) argue similarly and claim that the pro-life community is united in this opinion and working hard to get similar amendments passed in all states.
[4]   From the Spring, 1983 issue of Human Life Review, reprinted online at http://www.nationalreview.com/document/reagan200406101030.asp.
[5]   Probably the most frequently cited study is Diaz, S. et al., “Relative contributions of anovulation and luteal phase defect to the reduced pregnancy rate of breastfeeding women,” Fertility and Sterility, Sept. 1992. Abstract available online at http://www.popline.org/docs/0971/076085.html.
[6]   Provided, of course, that the researchers do not figure out some way to simulate implantation and allow the embryos to grow into the stage beyond where twinning and recombination are possible, in which case the embryos might indeed reasonably be considered as persons.

This page copyright © 2008 Edward A. Morris.  Created November 3, 2008.  Last updated April 25, 2012.

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