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The First Fourteen Days of Human Life
The New Atlantis ^ | Number 13, Summer 2006, pp. 61-67. | Patrick Lee and Robert P. George

Posted on 09/06/2006 8:10:44 AM PDT by

In the debate about the moral standing of human embryos, some defenders of embryo-destructive research have claimed that human embryos are not human beings until implantation (i.e., when the embryo attaches to the uterus, approximately six days after fertilization), and others have claimed that they are not human beings until gastrulation (i.e., when the possibility of twinning no longer exists and the primitive neural streak first appears, approximately 14 days after fertilization). These claims have been repeated by policymakers, scientists, and bioethicists alike, yet they fly in the face of the embryological evidence. Seeing why will put the embryo research debate on a more solid biological footing.

Life Before Implantation

Over the past few years, Utah Senator Orrin Hatch has pushed aggressively for federal funding of embryo-destructive research. When it comes to abortion, Senator Hatch votes consistently pro-life; he believes we have a moral obligation to protect developing human beings. But he also believes that embryos produced outside of a woman’s body, whether by cloning or in vitro fertilization, are not human beings unless or until they are implanted in a uterus. “At the core of my support for regenerative medicine research,” he declared in 2002, “is my belief that human life requires and begins in a mother’s nurturing womb.”

More recently, William Neaves, president of the Stowers Institute for Medical Research in Kansas City, has similarly claimed in public hearings that the embryo does not become a human being until implantation. According to Neaves, not until the embryo receives external, maternal signals at implantation is it able to establish the basic body plan of the human, and only then does it become a self-directing human organism. According to Neaves, these signaling factors somehow transform what was hitherto a mere bundle of cells into a unitary organism.

In reply to Hatch, Neaves, and others who make this argument, the first point to notice is that the standard embryology texts locate the beginning of the human individual at fertilization, not at implantation. See, for example, William J. Larsen, Human Embryology, 3rd ed. (2001); Keith Moore and T.V.N. Persaud, The Developing Human, Clinically Oriented Embryology, 7th ed. (2003); and Ronan O’Rahilly and Fabiola Mueller, Human Embryology and Teratology, 3rd ed. (2000). Most people who point to implantation as the beginning of an individual human life—Senator Hatch is a prime example—offer not the slightest bit of evidence to support their claim, relying instead on an alleged intuition. But since such intuitions can be matched by contrary intuitions, and since the alleged intuitions of Hatch and others contradict the evidence supplied by embryological science, they have no evidential weight whatsoever.

Neaves does offer an actual argument, but it is severely flawed. He claims that at implantation maternal signaling factors transform a bundle of cells into a human organism. But there is much dispute about whether any such maternal signaling actually occurs. As Hans-Werner Denker observes, it was once assumed that in mammals, in contrast to amphibians and birds, polarity in the early embryo depends upon some external signal, since no clear indications of bilateral symmetry had been found in oocytes, zygotes, or early blastocysts. But this view has been revised in light of emerging evidence: “[I]ndications have been found that in mammals the axis of bilateral symmetry is indeed determined (although at first in a labile way) by sperm penetration, as in amphibians. Bilateral symmetry can already be detected in the early blastocyst and is not dependent on implantation.”

Denker refers specifically to the work of Magdalena Zernicka-Goetz and her colleagues at Cambridge and that of R. L. Gardner at Oxford, which shows that polarity exists even at the two-cell stage. Davor Solter and Takashi Hiiragi of the Max Planck Institute for Immunobiology in Freiburg dispute these results, arguing that in the early embryo (prior to compaction and differentiation into inner cell mass and trophoblast) external factors determine the fate of each cell, rather than an internal polarity. As Gretchen Vogel reported in 2005 in Science magazine, embryologists are “polarized over early cell fate determination.” It is no longer taken as certain that the bilateral polarity of the embryo does not occur in the very first cleavages.

Moreover—and more importantly—even if it is the case that polarity does not emerge until a maternal signal is received at implantation, that would not provide any evidence at all that such a signal transformed a bundle of cells into a unitary, multicellular human organism. Rather, just as the lungs begin to breathe at birth only in response to certain external stimuli, so it would make sense that differentiation into the rudiments of the distinct body parts (basic bilateral polarity) would begin only in response to some external stimuli. And this is exactly how such signals speculated to occur (perhaps) in mammalian embryos are interpreted by the embryology texts that mention them. Thus, Neaves not only treats uncertain data as definitive, but—more to the point—his claim fails to hold up even if, for the sake of argument, one grants his assumptions.

The last point in reply to the claim that the human being is not generated until implantation is the most important one: there is complex and coordinated development from day 1 to day 6, much of it plainly oriented to preparing the embryo for the implantation process, as well as for processes that will occur only after that. The proposition that the human organism does not come to be until implantation (day 6) offers no explanation for this regular and ordered development.

On day 3 or 4 compaction occurs, which is the process in which the cells change their shapes and align themselves closely together. And compaction is the first step toward cavitation—the process (at day 4) in which an inner cavity is formed within the embryo and the embryo differentiates itself into the inner cell mass (which will later develop into the body of the mature organism) and the trophoblast (which will later develop into the placenta, a temporary organ of the embryo, equivalent to other temporary parts of the body, like baby teeth). On day 5 or 6, as the embryo enters the uterus, it “hatches” from the zona pellucida—the membrane enveloping the ovum that the sperm had to penetrate for fertilization to occur—preparing to begin implantation. At the same time, the trophoblast cells secrete an enzyme which erodes the epithelial lining of the uterus and creates an implantation site for the embryo.

In addition, the trophoblast itself becomes differentiated (about day 3 or 4) into various levels (cytotrophoblast and syncytiotrophoblast) in preparation for developing the vital contacts with the mother’s blood system (the embryo will circulate its own blood but will exchange oxygen and wastes with the mother’s blood, first through connecting microvilli, and eventually through the umbilical cord, developed from the trophoblast). Around the same time, the trophoblast produces immunosuppressive factors signaling the mother’s system to accept the embryo rather than attack it as a foreign substance. In order for the embryo as a whole to survive, this complex series of activities must occur in a timely, ordered sequence and with predictable regularity. Clearly, these activities—compaction, cavitation, and implantation itself—are organized processes performed by the embryo as an organismal whole.

The test of whether a group of cells constitutes a single organism is whether they form a stable body and function as parts of a whole, self-developing, adaptive unit. Compaction, cavitation, the changes occurring earlier to facilitate these activities, and implantation—all of these activities are clear cases of the cells acting in a coordinated manner for the sake of a self-developing and adaptive whole. In other words, such activities are ordered to the survival and maturation of the whole, existing embryo. This fact shows that the unity of the blastomeres (the cells of the early embryo) is substantial rather than incidental; the blastomeres are integrated parts of a functional whole, not separate parts that lead to the creation of a whole. This is compelling evidence that what exists from day 1 to day 6 is not a mere aggregate of cells but a multi-cellular organism.

Of course, one might object that even if there is an organism from day 1 to day 6, perhaps it is not the same as the organism after day 6. Perhaps implantation and its concomitant events produce a substantial change, the generation of a new organism. In reality, however, the direction of the growth between day 1 and day 6, on the one hand, and from day 6 onward, on the other hand, is the same. That is, the sequence of steps in the embryo from day 1 to day 6 is necessary and preparatory for what occurs afterward, and is a unitary trajectory of development. It is unlike, for example, the separate sequences of events undergone by the sperm and the ovum, respectively, before fertilization. Gametes (sperm and ovum) are oriented to joining with each other, actions that are performed not by them as a single unit, but by the maternal and paternal organisms (i.e., the mother and father). The sperm and the ovum (prior to fusing) are distinct biological parts of the distinct parent organisms (even though in coitus a type of organic union is effected between the male and female organisms). By contrast, the human embryo’s cells (from day 1 onward) form a stable body and work together to produce a single direction of growth, which is toward the maturation of the human organism.

The actions of the embryo from day 1 to day 6 are clearly part of a unitary development toward human maturation. None of the events occurring in the embryo could reasonably be interpreted as creating a new and distinct direction. Implantation does not change the nature (kind of being) of the embryo; it is an event in the unfolding life of a whole human organism, not the initiation of an entirely new organism.

Life Before Twinning

Another attempt to locate the beginning of the human being after fertilization is based on the rare phenomenon of monozygotic twinning and the even rarer phenomenon of fusion. Monozygotic twinning occurs when embryonic division results in two whole embryos. Apparently, fusion can also occur in humans: that is, two embryos can fuse to become one embryo. Such twinning and fusion are possible up to approximately day 14, with the appearance of the primitive streak, the visible precursor of the spinal cord and brain. Some argue that the possibility of twinning or fusion shows that prior to day 14 the embryo is not an individual; the individual who is clearly present at more mature stages of development has not yet come to be. Raymond Devettere expresses the argument clearly:

If we say a zygote is one of us, then we are also saying that one of us can become two of us, and that two of us can become one of us. This makes no sense. The possibility of the zygotes’ splitting or fusing suggests the zygote is not yet what we mean by one of us.

The puzzle, some seem to suppose, is that if we trace someone’s life back to adolescence, then to infancy, then to fetal existence, and then back to the embryonic stage, it does not seem as though the individual’s life traces back to fertilization. The tracing, in some cases, seems to stop at twinning or fusion.

But there is no puzzle here. Although twinning and fusion raise interesting questions about the details of early embryonic life, the argument that an individual life is not yet present is simply fallacious. Rather, in twinning, either the first embryo dies and gives rise to two others, or the first embryo continues to live and a second embryo is generated upon the splitting of the first one. We think the latter alternative is more likely, that twinning is (like induced cloning) a type of asexual reproduction in which the second embryo is reproduced asexually. For although monozygotic twinning can occur at the two-cell stage, most monozygotic twinning (at least two-thirds) occurs between days 5 and 9. In those cases, the growth trajectory of the original embryo continues, though the separation of some of the cells from the inner cell mass generates another embryo, with a distinct development trajectory. (If the splitting occurs after day 9, the embryos may share some of their permanent organs, resulting in conjoined twins, which are two distinct organisms that possess some degree of organic union.) The possibility of embryo fusion also poses no difficulty for the individuality of the embryo from day 1. If fusion in fact occurs, one embryo is absorbed into the system of another.

In a recent issue of Commonweal, Cathleen Kaveny attacks the position that an individual human life begins at fertilization, as it was articulated years ago by Germain Grisez:

Grisez’s attempt to preserve the claim that individuated human life begins at fertilization [by arguing, as we have, that twinning is a type of asexual reproduction] sacrifices too much of what we know about human nature—both from a Christian perspective and a scientific one. After all, human beings reproduce sexually, not asexually. Humans are mortal; they die and their bodies disintegrate. They don’t split neatly into two twins with no loss, cost, or remainder (as in twinning), nor do they merge fluidly into one another (as in combination).

Here we have a parade of assertions presented as if they constituted an argument. To assert that human beings never reproduce asexually is no argument at all, but simply a denial of the opposite position. Asexual reproduction is not the norm in humans, but embryological evidence shows that human beings in the early embryonic stage possess the capacity for asexual reproduction—a capacity that requires special environmental circumstances to induce it. Likewise, to say that when humans die their bodies always disintegrate, that their cells could never be absorbed by another, is just presupposing the falsity of the contrary position, rather than coming to terms with the scientific facts on which it is based.

When Kaveny asserts that our position “sacrifices too much of what we know about human nature—both from a Christian perspective and a scientific one,” she gives no indication of how it is supposed to conflict with Christian teaching. However, what we know about human nature from a Christian standpoint is fully compatible with the position set out above: namely, that a human individual is present even while the possibilities of fusion and twinning remain. Let us assume that each human being receives a rational soul when he comes to be. Just how he comes to be (whether immediately at fertilization or a few days later upon a splitting off of some of the first embryo’s cells) is irrelevant to that belief. And from a scientific standpoint, the position we have set out provides an intelligible explanation of the coordinated development of the embryo from day 1 up to twinning, should twinning occur, whereas the denial that there is an individual human organism prior to that point leaves such detailed coordination inexplicable.

Viewed biologically, the occurrence of monozygotic twinning and the possibility of fusion fail to show that in the first fourteen days the cells within the embryo constituted only an incidental mass. Just as the division of a single, whole flatworm into two whole flatworms does not show that prior to that division the flatworm was not a unitary individual, just so with the human embryo that twins. Parts of a flatworm have the potential to become a whole flatworm when isolated from the present whole of which they are part. Likewise, at the early stages of an embryo’s development, the degree of cellular specialization has not progressed very far (even if the process of orderly cellular activity is underway from the beginning), which means the embryo’s cells or groups of cells can become whole organisms if they are divided and have an appropriate environment after the division. But that does not show that prior to such an extrinsic division the embryo is a mere mass of cells rather than a single, complex, actively developing human organism.

There is additional, decisive evidence for this point: if the individual cells within the embryo before twinning were each independent of the others, there would be no reason why each would not regularly develop on its own. But as we know, these allegedly independent, non-communicating cells actually function together to develop into a single, more mature member of the human species. This fact shows that interaction is taking place between the cells from the very beginning (even within the zona pellucida, before implantation), restraining them from individually developing as whole organisms and directing each of them to function as a part of a single, whole organism identical with the zygote. This means that prior to an extrinsic division of the embryo’s cells resulting in the existence of a twin, these cells together constitute a single organism. And prior to the (even rarer) event of fusion, the twin embryos that fuse are distinct, whole organisms exhibiting active development.

Scientific Truth—or Utility?

Science has not solved every mystery of early human development. But human embryology has advanced sufficiently to enable us to dismiss certain fallacies about when a new human life comes to be. We do not doubt the good faith of those who believe that individual life begins at implantation or after the powers of twinning and fusion have passed. But arguments advanced to support these beliefs collapse under scrutiny. We must not let the desire to use human embryos in research obscure our grasp of what those embryos truly are from day 1: namely, nascent members of the human species, worthy of that fundamental respect and protection that justice demands for every member of the human family.

Patrick Lee is professor of bioethics at the Franciscan University of Steubenville in Ohio. Robert P. George is the McCormick Professor of Jurisprudence at Princeton University and a member of the President’s Council on Bioethics.

Patrick Lee and Robert P. George, "The First Fourteen Days of Human Life," The New Atlantis, Number 13, Summer 2006, pp. 61-67.

TOPICS: Culture/Society
KEYWORDS: embryo; embryos; escr; life; prenataldevelopment; prolife

1 posted on 09/06/2006 8:10:47 AM PDT by
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PDF of article

2 posted on 09/06/2006 8:11:28 AM PDT by (A Catholic Respect Life Curriculum is available at
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Though very technical, it is worth reading, because it confirms, yet once again from a scientific standpoint, that life begins at the very moment of conception.

Human Personhood Begins at Conception

3 posted on 09/06/2006 8:15:18 AM PDT by (A Catholic Respect Life Curriculum is available at
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Must be shocking to those who mock God, but He declared that He creates man in the womb and "scientists" keep discovering that, while the Bible is not a science book, when it speaks on science - it is Truth.

4 posted on 09/06/2006 8:15:43 AM PDT by Manfred the Wonder Dawg (Test ALL things, hold to that which is True.)
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To: Coleus; nickcarraway; narses; Mr. Silverback; Canticle_of_Deborah; TenthAmendmentChampion; ...

Please Freepmail me if you want on or off my Pro-Life Ping List.

5 posted on 09/06/2006 8:16:32 AM PDT by (A Catholic Respect Life Curriculum is available at
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Life begins at conception—NOT birth.
Birth is one day in the life of a person who is already nine months old.

6 posted on 09/06/2006 8:27:36 AM PDT by (A Catholic Respect Life Curriculum is available at
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Funny thing, the old Israel (the Israel of God) believed this.

The Israel of today (the Israel of Talmud) does not.

7 posted on 09/06/2006 8:36:44 AM PDT by Spirited
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To: Spirited
Yes it is very sad.

"Abortionists kill more children than terrorists" - Rabbi Yehuda Levin "He who destroys his own children…who wrecks the handiwork of G-D…brings hunger, plague, and the sword upon the world." -Zohar, Shemos (Exodus)

"Abortion is murder, plain and simple." -Rabbi Moshe Sternbuch, Da Ma Shetoshiv

The Silent Holocaust in Israel

8 posted on 09/06/2006 8:41:10 AM PDT by (A Catholic Respect Life Curriculum is available at
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Life clearly DOES begin at conception, when for the first time the new individual takes physical form from the seed of both mother and father. But this is also the beginning of the most hazardous journey of that life, one that most do not survive. Implantation is not a rare event, of course, but few manage it successfully, and those that do not certainly perish.

Is this merely disposing of an empty vessel, or is it truly death - the departure of a soul from the body? Well, why would it NOT be death? I doubt there is any shortage of souls, so why would an omnipotent G_d be parsimonious with them? And surely a merciful G_d would provide a place for so many innocents.

9 posted on 09/06/2006 8:49:04 AM PDT by MainFrame65
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To: MainFrame65

Excellent points. It is we poor humans who are generally so unmerciful.

10 posted on 09/06/2006 8:54:16 AM PDT by (A Catholic Respect Life Curriculum is available at
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"I knew you before I knit you together in your mother's womb"

Darkness, as defined, is the absence of light.


11 posted on 09/07/2006 6:31:07 AM PDT by woollyone (Preacher; "If there was more love in the world, there'd probably be a lot less dyin'")
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To: 2ndMostConservativeBrdMember; afraidfortherepublic; Alas; al_c; american colleen; annalex; ...

THE CODE FOR HUMAN LIFE we were once a fertilized egg, a blast, once an embryo, once a fetus, human, with our very own Human DNA since conception.  We were once microscopic-Americans. Once we have our own human genetic code, we are metabolizing as a single-cell entity, we are a living human being, therefore; we are a human be-ing that is biologically and scientifically testable.   At that moment we have that inalienable right to: life, liberty and the pursuit of happiness and property.   

The right to life is considered the most fundamental inalienable right there is.  Therefore, no one can determine when that right begins and no one can give that to you.  You have it when you become a human at conception.  When you get your full human genetic code.  Unmistakable to be matched to any other species, you’re human. 

Because of the intrinsic dignity of each and every person, each individual has certain rights and obligations, which every other individual would have to respect.   This is what’s required in order to live as a human, as the Lord Himself wanted it to be lived. (CCC) Created in the image of the one God and equally endowed with rational souls, all men have the same nature and the same origin. Redeemed by the sacrifice of Christ, all are called to participate in the same divine beatitude: all therefore enjoy an equal dignity.  

Inalienable rights belong to us by our very nature and existence; we are human and have that intrinsic dignity of a human being; we automatically have these intrinsic rights. No human being gave us these rights; they came from God.   So, we humans all owe each other certain inalienable rights which belong to us by our very nature and existence, by the fact that we are human and that we exist.  By the fact that we have the intrinsic dignity of a human being and that we exist, we automatically have these rights because of that intrinsic dignity, period. 

12 posted on 09/07/2006 9:59:19 PM PDT by Coleus (RU-486 Kills babies and their mothers, Bush can stop this as Clinton allowed through executive order)
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"The inalienable rights of the person must be recognized and respected by civil society and the political authority. ... Among such fundamental rights one should mention in this regard every human being's right to life and physical integrity from the moment of conception until death" (CCC-2273).

"Since it must be treated from conception as a person, the embryo must be defended in its integrity, cared for, and healed, as far as possible, like any other human being" (2274).

13 posted on 09/07/2006 9:59:50 PM PDT by Coleus (RU-486 Kills babies and their mothers, Bush can stop this as Clinton allowed through executive order)
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To:; syriacus

Freeper Syriacus once offered the analogy of 'would you shoot into a box if you weren't sure it was empty, and then if you wouldn't shoot into the box under those circumstances, would you shoot into the same box if you didn't know whether there was more than one person in the box?... As a refutation to the notion that embryos should be fair game for killing and exploiting so long as they are young enough that twinning could still occur. [I think I got that right ... perhaps you could correct me, syriacus.]

14 posted on 09/07/2006 10:26:24 PM PDT by MHGinTN (If you can read this, you've had life support from someone. Promote life support for others.)
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To: Coleus

Even in the morula age, as the newly conceived human life is moving along th fallopian tube toward the uterus, the embryo/morula is poerforming purposeful actions as an organism, for it is preparing itself to hatch from the zona pellucida and implant in the uterine lining, and this process cannot be accomplished until the new life has differentiated certain cells to accomplish the release of enzymes necessary for the preparation of the uterine tissue! That there may actually be two humans in that early cell structure, with one about to emerge but not yet seen doesn't mean the life is less human, less at least one human being.

15 posted on 09/07/2006 10:31:47 PM PDT by MHGinTN (If you can read this, you've had life support from someone. Promote life support for others.)
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Thanks for pinging me to this wonderful article, MGinTN.

I hope to have the time to read it with more thought.

Yes. I did say that you don't shoot at a box if you suspect there might be a child within.
And you don't say, "There might be two or three children inside, not just one, so it's okay to shoot at the box."

The humanity of the contents is what counts, not the number of humans.

So, what if at one moment you have one human embryo, and at the another moment you have two, and then at another moment you have one never have "no" embryos.

16 posted on 09/08/2006 4:21:02 AM PDT by syriacus (Why wasn't each home in New Orleans required to have an inflatable life boat?)
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I've bookmarked this great article, It's filled with great arguments and great details and I'm sure it will come in handy for future reference, too.

17 posted on 09/08/2006 4:28:35 AM PDT by syriacus (Why wasn't each home in New Orleans required to have an inflatable life boat?)
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And from what I understand, right after conception, it's the father's DNA, the father, who protects that new human life from the mother's immune system and is responsible for building the chorion, amnion and the other layers that make up the placenta.
18 posted on 09/08/2006 7:03:46 AM PDT by Coleus (Roe v. Wade and Endangered Species Act both passed in 1973, Murder Babies/save trees, geese, algae)
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To: Manfred the Wonder Dawg
Must be shocking to those who mock God, but He declared that He creates man in the womb and "scientists" keep discovering that, while the Bible is not a science book, when it speaks on science - it is Truth.

But this article refutes the idea that life begins in the womb. It states that life begins at conception, which naturally occurs within the fallopian tube, or artificially occurs in vitro.

19 posted on 09/08/2006 7:16:04 AM PDT by Caesar Soze
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To: Coleus

That is my understanding as well.

20 posted on 09/08/2006 9:32:15 AM PDT by MHGinTN (If you can read this, you've had life support from someone. Promote life support for others.)
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