Theology of Twinning

Issue #44

Last Update March 2, 2006

Religion On the Theological Implications of Twinning by Esau Isaaksen June14, 2005 Church doctrine holds that the soul enters the body at conception. Other religions that have a concept of soul assign different timings to its acquisition; Judaism and some segments of medieval Christianity regarded the eighth day, when the survival of the infant was more certain, as the correct time. Nevertheless, the moment of conception has been settled doctrine for some time. It is this, more than any concern for the sanctity of life, that is behind the Church's unyielding opposition to abortion; a being with a soul is human, while one without one is a mere animal, however human its form.

Certain problems are presented, however, by the natural process of twinning. Artificial human cloning is a complex subject that will not be considered here; twinning, or natural cloning, has been with us since the beginning of the human race, but I don't believed the theological issues have ever been addressed. The critical issue, and the one that is the focus of this paper, is that of the status of the soul of a twin.

Fraternal twins are not part of this problem. The result of two separate fertilizations of two separate eggs by two separate sperm, fraternal twins are two separate conceptions, and thus each has its own soul. Identical twins are another matter entirely.

We may distinguish two different kinds of identical twin: the somatic twin and the spiritual twin. Let us consider the somatic twin first.

The somatic twin is the common identical twin. After conception, the gamete splits and each portion develops separately into two individuals with a common genetic inheritance. Although only one soul was provided at the moment of conception (since there was only a single conception), four possibilities exist for these twins: (1) after the split, one twin retains the soul while the other twin is soulless; (2) God in his Mercy provides a second soul for one of the twins, while the other retains the original soul; (3) at the time of the split the soul splits as well, but develops as a complete soul, just as the bodies develop as complete bodies, resulting in two identical bodies with two identical souls; or, finally, (4) when the gamete splits the soul splits, leaving each twin with half a soul.

If (1) is truly the case, then we have one human being and one soulless animal in human form. This may account for the Good twin/evil twin dichotomy so beloved of fiction writers. Is is possible to determine which twin has the soul, and which twin is soulless? Is it permissible to destroy the soulless twin? Is it desirable to do so? Is it required?

If (2) is the case, there is no real problem, since both twins are truly human. In this case, the bodies are identical but the souls are different. Could this be the real cause of behavior differences which, in twin studies, is assigned to subtle environmental influences as the twins matured?

If (3) is the case, again there is no problem, with both twins truly human and sharing identical bodies and souls. Could this be the reason that identical twins are often credited with almost mystical communication and closeness?

If (4) is the case, is either twin truly human? What does it mean to have half a soul? Is the soul's communion with God impaired? Is half a soul immortal? Are there qualities to the soul that are parceled out, some to one twin and some to the other, or is the soul an undifferentiable thing, attenuated by being split?

Spiritual twins arise by an entirely different bodily process. Dual ovulation often occurs; if both eggs are fertilized, fraternal twins result. Occasionally, however, One of the fertilized ova is absorbed by the other, resulting in a teratogenic person, with some cells having the genetic content of one “twin” and some cells having the genetic content of the other. A case of this type made the news recently when tissue typing done to determine suitability for a transplant showed that, amazingly, the father of the transplant recipient was indeed the genetic father, but the mother, who had given birth to the child, was not the genetic mother. Further testing demonstrated that cells from different parts of the mother's body had different DNA, some cells proving that the mother was the genetic mother, and some showing that she was not. In this case, doctrine would hold that there were two souls originally, as there were two conceptions. Again, several possibilities exist for the dispositions of these souls: (1) both souls persisted after the absorption, resulting in a person with two distinct souls in one body; (2) one soul absorbed the other, as one embryo absorbed the other; or, (3) one soul remained with the body, while the other went to its eternal reward.

If (1) is the case, what is the effect on the person of having two souls? Do they always act in concert, or are inter-soul struggles possible? Is one dominant over the other? At the end of life, do both suffer the same fate, damned together or saved together? If the person commits evil, which soul was the cause? Is there as possibility for greatness from having an extra soul? Would that person have to take Communion twice, once for each soul?

If (2) is the case, is the resulting soul a hybrid, as the body is a hybrid? If so, just what does that mean? (As with the question of half-souls, is the soul at all divisible?)

If (3) is the case, the individual present no problem, being one person with one soul. But which soul is selected to remain, and which soul is selected to pass on to eternity? How is this selection done? Is it possible for a body 90% from one embryo and 10% from the other to end up with a soul that originated with the minority constituent? In effect, the body would have the wrong soul, someone else's soul. What would that feel like?

Further investigation of Church doctrine is needed to resolve these issues. Before pronouncements are made concerning the evils of cloning (which, depending on the answers gleaned from contemplation of natural twinning may turn out not to be evil after all), a consistent, rational doctrine of twinning needs to be created.