Souls of identical twins
Question from Pete on 3/2/2008:

Dear Judie,

I'm taking a University course in Psychology, and I'm reading about how stem cells might be used to heal problems with the brain and nervous system. The book mentions how George W. Bush and the late Pope John Paul II (among many ethicists and religious leaders) have raised moral objections to embryonic stem cell research.

I know that most Catholic theologians are in agreement that an embryo receives a soul from God at the moment of conception. Hence they are a person from the very beginning of pregnancy.

My course textbook asks the question of whether embryos are people. It states that the government of the United Kingdom considered the available evidence. The evidence goes to say that, in the first 14 days following fertilization, the embryo can go through many changes, such as splitting into twins or recombining back into one embryo, that make it difficult to accord to it the status of an individual human being. It states that, from this perspective, conception of a person does not happen in an instant but occurs over 14 days.

So, do you know what this implies for the Catholic perspective that a person has a soul from conception? In particular, so it's not certain whether an embryo is a person before 14 days? So then wouldn't abortion not really be murder before then? Can you please tell me how an embryo which splits into identical twins, can still be a person before that split? How about the soul, so do those embryos only receive souls after that split? So, hypothetically, using say the morning-after pill would not be considered abortion in this case?

Going further, I guess, what if the twins recombine into one embryo, so would the twins then not even have a soul until that recombination? So, wouldn't God have to wait perhaps 14 days, until it's definitely decided whether there will be twins or not, for instance? I'm a little confused actually.

I checked online, and I saw 2 Catholic views for this last case. One is that God knows whether there will be twins or not from the very conception, and waits until then. The other view I saw is that God creates one soul, then makes a 2nd one when the twin is created, and when they recombine, kills the 2nd zygote. I also remember reading that St. Thomas Aquinas held a minority view, based on Aristotle's biology, that the body only receives a soul 40 days after conception.

That confuses me even more. Do you know perhaps any scientifically informed Catholic views or website on this that are approved by the Church, say? Perhaps any saints or Church doctors or Fathers, whose views might be relevant here? Perhaps a view cited by the Pope? I'm just confused and hoping you could help me clear things up.

Thank you very kindly and God bless you, Pete

Answer by Judie Brown on 3/2/2008:
Dear Pete

The simple response to your question is that the textbook is totally inaccurate. If you want to read a concise, accurate presentation on when a human being begins, I can refer you to the writings of two remarkable scientists:

Dianne Irving, PhD C. Ward Kischer, PhD

Their articles on these subjects are searchable at http://www.lifeissues.net/

The specific question you ask on twinning is addressed by both scientists, and to give you but one excerpt from an article by Kischer (http://www.lifeissues.net/writers/kisc/kisc_10humandevelopment.html):

Developmental Individuality McCormick's reliance on developmental individuality is derived from Grobstein's recently published "stages".15,16 Grobsteint17,18 claims the stage of developmental individuality is reached when division of the inner cell mass no longer can divide to produce twins or multiple identical individuals. Ancillary support for this contention comes from a report by the American Fertility Society, which states that at least up to the eight-cell stage the developmental singleness of one person has not yet been established.22 This, quite simply, is not true. Seventy percent of all identical twins (monozygotic origin, that is, derived from one fertilized egg) are accounted for by division of the inner cell mass. The other 30% are accounted for by division at the two-cell to eight-cell stage of cleavage.20,21 Multiplicity of birth from dizygotic origin (two different ova) appears to be familial. However, the factors determining the origin of monozygotic multiplicity are not known, but, statistical data does not support a familial origin. The fact that 30% of all monoygotic twinning is determined in early cleavage stages strongly suggests that the singleness of all cases other than monoygotic twinning is determined at fertilization, or, perhaps at the first cleavage division. Compounding the problem explaining the onset of individuation is the fact that multiplicity beyond twinning may include a combination of diygotic and monoygotic-derived embryos.(21)

The fact is, not a shred of evidence exists which would explain the origin of monoygotic multiplicity. The kind of evidence which McCormick needs to support singleness occurring at the inner cell mass stage, and which would justify his "new moral status", is simply not in existence.

The overwhelming majority of individuals on this earth now and since the beginning of hominid development have been, and are, derived from one fertilized egg without further separation of the blastomeres. If exceptions to this fact prompt a new definition for the right of ensoulment, it would be done for a very small fraction of the total human population now and in the future. Further, there would be no certain way ethically to withhold ensoulment from stages prior to formation of the blastocyst, because the factors or stimuli which produce monoygotic twins are not known and therefore not predictable.

By designating developmental commitment to a single individual (singleness) as a determining factor for ensoulment, then in cases in which totipotentiality is lost early in development (called determinant cleavage), for example, in the annelids (worms), would there be an entitlement to ensoulment? Certainly there has never been a suggestion that the Catholic Church, nor any traditional religion, should recognize ensoulment for other than humans. Therefore, it would seem that the human quality would have to exist. This quality is established at fertilization. But, by qualifying this entitlement and restricting it to a later stage, such as the inner cell mass, the human quality is thereby equivocated. Indeed, a stronger case can be made for developmental individuality occurring at the time of fertilization of the ovum rather than at the inner cell mass stage.

McCormick states that the potential for a fertilized egg to become an adult is a theoretical and statistical potential because only a small minority actually achieve this in the natural process.(22) But, so what? What does that have to do with those zgotes which do successfully develop? A significant number of zgotes, embryos, fetuses and born individuals encounter biological faults, many of which precipitate early death before and after the inner cell mass stage.

There are other significant facts about human development that are commonly misstated. For example, in the case of human development, we have traditionally believed in the totipotentiality of the cleaving blastomeres (cells) until the inner cell mass stage (the blastocyst). but, not each blastomere has the same potential as the zygote, not even in cases where subsequently there might be a division of the inner cell mass into multiple copies of the embryo. Some of the blastomeres are destined to assume a peripheral position of the cleaving mass. During the formation of the blastocyst, these peripheral blastomeres will assume the identity of the trophoblast. The innermost blastomeres correspondingly, become distinguished from the peripheral-most cells by forming the inner cell mass. Positional differences are not to be exempted from consideration of totipotentiality.

McCormick states the organization of the inner cell mass into two layers (referred to as the bilaminar embryo) is reflected by the formation of the primitive streak.23 That is incorrect. The appearance of the streak marks the beginning of the formation of the trilaminar embryo.

It has also been reported by Short that it is untrue that identical twins may have progressed through two distinct inner cell masses at the fifth day.24 They certainly could have and could have been derived from separate earlier stages, which would have been derived from early monoygotic twinning.(20) Short also states if "cleavage of the embryo is delayed until eight or more days after fertilization, the two resulting embryos have come from a single inner cell mass, and share one common set of all placental membranes." If twinning is delayed until eight or more days after fertilization, the two resulting twins will share a common placenta, but also a common amnion. They represent an anomalous condition and are rarely born alive.(20)

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Judie Brown