Recently, scientists have reported some important findings from experiments conducted upon human stem cells. These results, we are told, signal the potential discovery of treatments for a number of dreaded diseases. Yet the stem cells used in these studies are usually taken from aborted fetuses or from embryos (zygotes) created in the laboratory. According to Jewish law and tradition, is it permissible to utilize human embryos and aborted fetuses in stem cell research?
1. The Scientific Background
. Stem cells are a type of cell found in the human body at all stages of development: embryonic, fetal, and adult (in this context, an "adult" stem cell refers to a stem cell that occurs in the human organism after birth). While all other cell types, such as heart cells or skin cells, are specialized or committed to conducting specific biological functions, the stem cell is unique in that it is uncommitted to any specific function and remains so until it receives a signal to develop into a specialized cell. All stem cells are capable of renewing themselves and of becoming specialized or differentiated to yield the cell types of the particular tissues from which they originate; when the tissues become damaged or destroyed, the stem cells enable the body to restore them. Yet there are some important differences among these stem cells. Some stem cells are "pluripotent": i.e., they have the capacity to develop into almost all of the more than 200 different known cell types. Stem cells that display this characteristic come from embryonic or fetal tissue. Adult stem cells do not have this capacity. Adult stem cells do possess to some extent a characteristic called "plasticity," the ability of a cell type derived from one tissue to develop into specialized cell types of another tissue. To date, however, it has not been demonstrated that the adult stem cell can be directed to develop into any cell type of the body.
During the past few years, researchers have succeeded in isolating pluripotent stem cells from the early (4- to 5-day) human embryo (called the blastocyst) and in growing them in a laboratory setting. This is a dramatic development, one that may well portend some significant advances in medicine and health. A number of deadly illnesses-among them Parkinson's disease, Alzheimer's disease, diabetes, chronic heart disease, liver failure, cancer, multiple sclerosis, and spinal cord injury- ravage the body by destroying organs and cell tissue. Scientists hope either to cure or to control these diseases by manipulating stem cells to generate new tissue to replace that which the diseases have destroyed and to restore vital bodily functions. In addition, as this technology becomes more advanced, it is possible that whole organs might be created for use in transplantation, a critical desideratum given the ongoing shortage of donor organs available for this purpose. Finally, the study of embryonic stem cells can help us gain a better understanding of genetics and human development, including the causes of birth defects, and consequently aid us in the effort to correct or prevent them.
2. The Moral Challenge
. Stem cell research, therefore, is fast emerging as one of the most hopeful fronts in our age-old battle against disease, and we are properly encouraged by its progress. Our happiness, however, is tempered by our concerns over the nature of this research, particularly as it involves fetal and embryonic stem cells. (The derivation of adult stem cells does not pose similar concerns; as we have noted, however, fetal and embryonic stem cells offer much better prospects for research.) In order to derive fetal stem cells, scientists must utilize aborted fetuses. In order to derive embryonic stem cells, they must destroy the embryo; that is, they must kill the human organism at its earliest stage of development. Such laboratory manipulation of human fetuses and embryos raises questions of great moral seriousness, and we must not ignore these questions even when that research carries the prospect of important medical breakthroughs. On the contrary: the demand that we behave in an ethical manner, a demand that is central to our concern as religious people, does not cease to apply to us when we enter the laboratory. In our scientific lives, no less than in our social or political lives, we are required to ask whether our acts, no matter how well-intentioned, pass muster before the bar of morality. As Jews, in particular, we ask these questions from the standpoint of our participation in a tradition that has a great deal to say concerning the ethics of science and medicine.
What, then, should be our stance with regard to stem cell research? Is this procedure coherent with the duties imposed upon us by our Jewish moral tradition as we Reform Jews best understand it? Are we permitted to abort the human fetus and to destroy the human embryo for the purpose of medical experimentation? If so, are we permitted to create embryos and fetuses intentionally in order to use them subsequently in this manner?
These, as we shall see, are not easy questions to answer. While the answers we have arrived at represent in our view the best and most persuasive response to these questions, we do not claim to have resolved all problems with absolute certainty. Our chief hope, therefore, is that our teshuvah will suggest a fruitful way for us as Reform Jews to think and to talk about the moral issues connected with stem cell research. In that way, it may prove helpful to us as we continue our discussions and debates over this latest development in medical technology.
3. The Mitzvah of Medicine
. Jewish tradition holds the practice of medicine to be a mitzvah, a religious duty. The Torah, to be sure, does not explicitly enjoin us to practice medicine, and though the Rabbis deduce from Exodus 21:19 that the physician is permitted to ply his craft, they do not suggest that the verse obligates him to do so. That conclusion is left to the great post-Talmudic authorities, the rishonim, among them R. Moshe b. Nachman (Nachmanides or Ramban, 13th-century Spain). In his Torat Ha'adam Ramban writes that the "permission" of which the Rabbis speak is in fact a mitzvah, because medicine falls under the category of pikuach nefesh, the saving of life, an act that according to all opinions is most certainly a mitzvah and that takes priority over almost all other religious obligations set forth under the Torah. This understanding, which has been adopted by the leading halakhic compendia, reflects the predominant Jewish attitude toward the practice of medicine. Our tradition requires that we utilize our knowledge and our power to their utmost in order to heal the sick; "when one who delays in doing so, it is as if he has shed blood."
When we speak of the mitzvah of medicine, we have in mind more than just the dispensing of treatment to patients by physicians and other health care professionals. "Medicine" as we understand it today is a scientific discipline, defined by the canons and practices of a scientific community. Among these canons and practices is the insistence that medicine is an experimental science, founded upon extensive, carefully controlled laboratory and field research. It is this body of research, a continuing process of testing, verification, and discovery subject to the critical review of peer scientists, that commands our respect for the practice of medicine and that empowers physicians to speak and to act with authority. For these reasons, it is difficult to draw firm distinctions between the "pure" and "applied" aspects of medical science. The scientist who tests and develops a therapy is engaged in the mitzvah of healing just as surely as is the physician who administers it to the patient; the work of each is just as essential to the saving of human life as is the work of the other. If we define the administration of life-saving medical therapy as pikuach nefesh, we should not forget that physicians could not save lives were it not for the extensive scientific research upon which our contemporary practice of medicine is based. Since research into human stem cells partakes of the mitzvah of healing, surely our society ought to support it.
4. Jewish Tradition and Respect for Human Life
. Medicine, however, is not the only relevant aspect of the mitzvah of pikuach nefesh. The commandment to save life reflects our tradition's demand that we respect life and honor it. This implies an obvious limitation upon the way we are permitted to practice medicine: we are not allowed to commit murder, even if the shedding of one person's blood will lead to healing for another. This idea is linked in our classical texts to the concept of yehareg ve'al ya`avor: we recognize that there are certain actions we must never perform, even at the cost of our lives, because our covenant with God requires no less. In the present context, it teaches us that we may not practice medicine in such a way that is destructive of human life. For example, under certain carefully specified conditions it is morally permissible to conduct medical experimentation upon human subjects. Yet it is clearly forbidden to sacrifice the life of the subject, even if the therapy being tested has the potential to save many lives in the future, for we may not use murder as a means of healing. Does this rule hold in the case before us? Does the prohibition against murder, which protects the day-old infant, apply as well to the human organism in its prenatal stage? If it does, then it is difficult to imagine how stem cell research could be deemed moral from the standpoint of Jewish law.
Even if the destruction of the fetus or the embryo is not considered an act of murder under Jewish law, we cannot automatically conclude from that fact that the destruction is "permitted." The principle we call "respect for human life" is not identical with the prohibition against bloodshed. It reaches beyond the scope of specific prohibitions to touch upon our more general moral commitment to the sanctity of human life. To say that human life is sacred is to say that, at some definable point, it is inviolate, that it is protected and preserved from our power to control, to manipulate, and to destroy. How does this commitment inform our attitude toward prenatal life? Is our belief in life's sanctity compatible with laboratory experimentation upon-and the concomitant destruction of-the fetus and the embryo, even if that experimentation may lead to the discovery of life-saving medical therapies?
5. The Status of the Prenatal Human Being.
We are asking, therefore, whether and under what circumstances we may destroy the prenatal human organism for the advancement of medicine and, ultimately, the goal of pikuach nefesh. To answer this question, we must determine the status of the fetus and the embryo under Jewish law. Since we would never imagine that it is permissible to sacrifice the day-old infant "in the interests of science," we must ascertain whether the fetus and the embryo possess a status that is legally inferior to that of the infant. If its status indeed is a lesser one, then perhaps we are morally justified, under certain circumstances, in sacrificing the prenatal human being for the sake of medical research.
a. The Fetus
. The traditional Jewish discussion of the status of the fetus customarily begins with the following Mishnah:
"If a woman experiences life-threatening difficulty giving birth, the fetus is dismembered in her womb and removed limb from limb, for her life comes before its life (mipnei shechayeha kodmin lechayav). Once the major part of (the fetus) has emerged, it may not be harmed, for one person (nefesh) is not sacrificed on behalf of another."
The text clearly mandates abortion in this case, but the authorities disagree as to the grounds on which it does so. Maimonides sees the fetus as a rodef, a "pursuer" that threatens the life of the mother; like all pursuers, the fetus may be killed if necessary to save its victim from death. Rashi offers another interpretation: so long as the fetus has not emerged from the womb, it is not a nefesh, a full legal person, and the mother's life therefore takes precedence over its own. Once it has emerged, it acquires the status of a legal person; therefore, "one nefesh is not sacrificed on behalf of another." Rashi, in our view, provides the better and more coherent reading of the Mishnah's text. And while others may differ on that point, there is general agreement that Jewish law does not regard the fetus as a nefesh, a full legal person. For this reason, the killing of a fetus is not considered or punished as an act of murder under the halakhah. And since the fetus possesses a legal status inferior to that of the mother, a number of halakhic authorities permit abortions in situations where the mother's life is not endangered by the birth of the child but where the abortion is necessary for her physical or mental health. Given that the fetus does not enjoy the entire range of protections that Jewish law accords to the full legal person, we might conclude that it is permitted to abort the fetus in order to utilize its tissue for experimentation aimed at the development of life-saving treatments.
That conclusion, however, would be a hasty one. Though the fetus does not qualify as a nefesh, the halakhah nonetheless accords it a high degree of protection. We see this protection at work in both a negative and a positive context. The negative context is that Jewish law prohibits feticide in the absence of serious cause. Virtually all authorities hold this view, although they vigorously dispute the nature of the prohibition and the definition of the "serious cause" that overrides it. The positive context is that the laws of pikuach nefesh apply to the fetus: we are required to violate the laws of Shabbat or Yom Kippur if necessary in order to save its life. Even though the fetus is not technically a nefesh, it is in any event a potential person, a "nefesh in becoming," so that "we violate one Sabbath on its behalf so that it may one day keep many Sabbaths." The fetus may occupy a lower legal status than other human beings, but it is a human being; it partakes of the sanctity of human life, and it deserves our honor and respect.
Taken together, these two elements of Jewish teaching concerning the fetus can serve as a guide to our own conduct. Because the fetus is not a nefesh and because the mother's life and health takes precedence over it, we can confidently permit abortion in circumstances other than mortal danger to her. Yet because the fetus is a human organism, a "potential nefesh," we condone abortion only for truly weighty justifications; "we do not encourage abortion, nor favor it for trivial reasons, nor sanction it 'on demand.'" Specifically, abortion is indicated in order to safeguard the health of the mother or to spare her great physical or emotional pain. It is difficult to define a set of abstract rules governing the decision for or against abortion. That decision requires a careful consideration of the facts and circumstances of the particular case. Yet we have written that abortion should not be performed for reasons other than "serious maternal anguish," that is, a real set of difficulties faced by a particular woman. The destruction of fetal life for any other reason stands in direct conflict with our commitment to the sanctity of that life. We therefore cannot sanction abortion for the purpose of harvesting fetal tissue for use in medical experimentation, even though the goal of that experimentation is the advancement of science toward new life-saving therapies. On the other hand, if a pregnancy has been terminated for a reason that we would regard as morally sufficient, we are permitted to use the aborted fetus in medical experimentation. We have long approved of autopsies for scientifically valid purposes; the use of fetal tissue and organs would clearly qualify for the same approval, so long as the research is not the actual motivation for the abortion.
b. The Embryo
. What is the legal status of the embryo, the fertilized egg that does not reside in utero? This question poses a special difficulty for the halakhist. The classical sources certainly did not envision the possibility that a human embryo might exist and develop in a petri dish; how then can they speak to the legal status of that embryo? Contemporary authorities, however, note that while the sources do not discuss the embryo, they do discuss the case of the fetus at its earliest stages of development and that we can learn much from those discussions. The Talmud holds that prior to its fortieth day of gestation the fetus, lacking form, is to be regarded as "mere water" (maya be`alma). This determination has some significant legal consequencesand, most importantly for our purposes, figures prominently in the Jewish law of abortion. A number of decisors agree with the stance of R. Eliezer Yehudah Waldenberg that "when an abortion is indicated for medical reasons, it is best to perform it prior to the fortieth day of gestation. The law is much more lenient at that point inasmuch as the fetus prior to forty days is maya be`alma." We should be careful not to read too much into the forty-day distinction. The fact that abortion is easier to permit prior to the fortieth day does not mean that it is not prohibited at all. And the law of pikuach nefesh, which as we have seen applies to the fetus, presumably applies to any fetus, even for one that is less than forty days old. The distinction does indicate, though, that while we respect and honor human life from its conception, the human organism at this earliest stage of its development is seen as having a lesser or inferior legal status than that possessed by the fetus at a later stage. Its lesser legal status, in turn, suggests that it exercises a lesser claim to protection than it does subsequently.
How might this insight inform our understanding of the status of the embryo? An important ruling on this subject is that of R. Shmuel Halevy Wasner, who considers a question arising from the IVF procedure: does the law of pikuach nefesh apply to the zygote? Are we permitted to violate the laws of Shabbat if this is necessary to "save" the embryo and to allow it to continue its development in the petri dish? Wasner responds that, while we are required to do just that for the fetus, and apparently even for the fetus prior to its fortieth day of gestation, we are forbidden to violate Shabbat on behalf of the embryo that has not yet been implanted into the womb. He writes that the law of pikuach nefesh applies to the fetus, even though it is not a full legal person, because most fetuses will survive, be born, and become full legal persons. In Jewish ritual terms, the fetus will likely become a ben mitzvah, a person subject to the obligations of Torah; accordingly, we apply to it the principle "we violate one Sabbath on its behalf so that it may one day keep many Sabbaths." We cannot say the same of the zygote. We cannot say that most of these embryos will "likely" develop into persons (nefashot), because they lack the minimum qualification--implantation into the womb--that would enable us to make that statement. The embryo, therefore, possesses a legal status inferior to that of the fetus, and one element of this lesser status is that Jewish law imposes no positive duty to "save" its life.
If we have no duty to protect the embryo from death, it might follow that the halakhah does not explicitly prohibition its destruction. And if destruction is not explicitly prohibited, it might well be permitted under particular circumstances. For example, the procedure of in vitro fertilization (IVF) requires the creation of many more embryos than can be implanted into the womb of the woman who donated the eggs or of a "host mother." What shall we do with the "excess" embryos, those not used for implantation? Must we preserve them ad infinitum or may we discard them? Two leading contemporary halakhists rule that it is indeed permissible to discard these excess embryos: not only are they not "likely" to become full nefashot, there is no possibility that they will do so, since there is no intention to implant them. We owe no moral duty to these embryos, in other words, that would forbid us from discarding them.
This Committee has previously reached a similar conclusion. We hold that it is permissible to destroy excess embryos for two reasons. First, we accept the Jewish legal doctrine of the nefesh. "Personhood," according to this teaching, is a characteristic possessed exclusively by members of the human community, that is, by men, women, and children; the human organism does not become a full legal person until birth. This does not mean that we owe no moral duty toward the human organism prior to its birth; we most certainly do. We believe, however, that these obligations exist precisely because the fetus and embryo are "persons in becoming." The excess embryo, unlike the fetus or the embryo that is intended for implantation, has no potential to become a nefesh; therefore, while we would not condone its wanton destruction, we would permit it for causes of lesser gravity than those we would ask in the case of abortion. Second, the discarding of excess embryos is positively indicated as an important element of IVF. Were we to require that every one of these embryos be preserved, we would place a cumbersome burden upon hospitals and laboratories. Under such conditions, many of these institutions would likely refuse to perform IVF, thus rendering the procedure intolerably expensive or simply unavailable to many of those who seek it. The destruction of the excess embryos therefore serves to make possible the fulfillment of the mitzvot of healing and procreation. Moreover, we have extended this permit to cover medical experimentation: if Jewish tradition allows us to destroy these excess embryos, we think it would surely allow us to use them in experimentation aimed at the advancement of medicine, to the fulfillment of the mitzvah of pikuach nefesh. These embryos may therefore be utilized in human stem cell research. This opinion, we might add, is shared by other leading scholars in the field of Jewish medical law and ethics. This permit for the destruction of such embryos for research purposes would obviously extend to the use of existing stem cell lines, that is, stem cells that have already been derived and that are currently preserved in laboratories.
c. The Creation of Embryos for Medical Experimentation
. The human embryo is largely "unprotected" by Jewish law. There is no explicit halakhic prohibition against its destruction, and partly for this reason we feel morally confident about permitting the destruction of "excess" embryos created as part of the IVF procedure and about permitting the use of these embryos in medical research. Let us take our inquiry to its next logical step: would it be also permitted to create embryos explicitly for purposes of medical research? It is not difficult to sketch an argument in favor of a "yes" answer. Newly-created embryos, after all, are destined for the laboratory and not for the womb. Like excess embryos, they have no potential to develop into full human persons. If the lack of that potential leads us to permit the use of excess embryos in medical research, why shall we not say the same for embryos that are created for no other purpose than medical research? The analogy between the two sorts of embryos, however, is not tight enough to support that conclusion. We do not create excess embryos with the explicit intention to destroy them. They are the necessary and unavoidable by-product of the procedure of in vitro fertilization, which requires the creation of more embryos than can be utilized in the initiation of pregnancy. If we could perform IVF without creating excess embryos, we would do that; if we could use these embryos for other purposes or store them in an economically feasible manner so as to obviate the need for their destruction, we would do that. We permit the discarding of excess embryos, not because of their "inferior" legal status (though that low status does remove a major moral obstacle to their destruction), but because in order to make IVF available to those who seek it we have no choice but to discard them. Given that the excess embryos will in any event be destroyed, we think it is entirely proper that their destruction be accomplished as part of the research that might lead to the discovery of life-saving therapies. None of this requires the conclusion that we are permitted to create human embryos explicitly in order to destroy them, even for medical purposes. The analogy, in short, does not work.
On the other hand, we could argue for an affirmative response without resorting to analogies at all. We might reason in a more deductive fashion: if the mitzvah of pikuach nefesh overrides virtually all other religious and moral obligations imposed in the Jewish tradition, then surely it justifies the creation-and destruction-of human embryos in the name of medical science, particularly given the lack of any concrete prohibition against killing the embryo. This argument does have persuasive force, but that force lies in the sheer power of calculation. It depends upon the assignment of relative values to the human organism at different stages of its development: the nefesh receives a higher score than the not-yet-nefesh. It then imagines a conflict between the life of the nefesh and the life of the embryo, a conflict that the nefesh automatically wins. This mathematical approach is elegant in its simplicity, but in our judgment it is too simple, for it ignores some vital moral issues raised by the destruction of embryonic human life.
We repeat: embryonic human life. Let us not mince words. Although the fertilized egg may be called an "embryo," a "zygote," or a "blastocyst," these labels can mask the fact that we have here a human being, an organism that contains all the genetic material that would, under the proper conditions, develop into a full legal person. As a leading medical text puts it: "The time of fertilization represents the starting point in the life history, or ontogeny, of the individual." The embryo may not have attained the status of a nefesh, a legal person, a member of the human community, and its unwarranted killing may not be defined as "murder." It is, however, a human being, and by that token it partakes of the sanctity of all human life.
Rather than attempt to calculate the value of one human being against that of another, let us instead ask ourselves what this sanctity means. Before we say "yes" to the creation and destruction of human embryos, with all the marketing, trafficking and commercialization that would inevitably accompany their widespread use in laboratory research, let us consider what our commitment to the essential humanity of the embryo ought to demand of us. We Reform Jews might well answer that question in various ways. Yet even in its most minimal definition, sanctity requires the recognition that human life is at some point inviolate, that it lies beyond our reach and our manipulation. This inviolability is the single greatest moral distinction between human and all other forms of life. We accept the notion that animals can be brought into the world with the express purpose of being killed to serve our purposes. We do not apply that notion to human life, because our sense of the sanctity of human life calls forth from us a response of awe and reverence rather than dominion and utility. There is no reason to assume that this awe and reverence do not apply to human life even at the embryonic stage, for even there, in the microscopic fertilized egg, lies the supreme potential for humanity.
Differences in legal status do help us to make difficult choices. This is particularly true in the matter of abortion. It is precisely because the fetus is not classified as a nefesh that we are permitted to make the otherwise unjustifiable decision to sacrifice its life on behalf of the life, health, or extreme anguish of its mother. Yet that decision is made in light of the actual and direct danger that the continuation of the pregnancy poses to a particular woman. As we have suggested, the fetus's lower status would not justify its destruction for the sake of medical research that might yield results that might be helpful to some as-yet unknown persons in the distant future. We think that the same considerations apply to the embryo. The zygote's status under Jewish law may be lower even than that of the fetus; for this reason, we can countenance the destruction of excess embryos created as part of the IVF procedure and their use in medical research. We do not accept, however, that this lower status would permit us to create embryos for no other purpose than to destroy them in furtherance of research that might well not lead to therapeutic benefits for some unknown person in a far-off future. To permit that action would be to stretch the definitions of pikuach nefesh and refuah beyond plausible boundaries. To permit that action, indeed, would be incompatible with our commitment to the sanctity that inheres in these embryonic human lives.
We should emphasize, finally, that we speak here exclusively to the current scientific situation. The question before us has to do with experimentation, with the destruction of human embryos as part of a research protocol that might some day lead to discoveries that would offer therapeutic benefit to actual patients. It is because any such benefit is many steps and quite possibly many years removed from medical reality that we cannot apply to that research the designation of pikuach nefesh. Were that reality to change--specifically, were science to develop from stem cell research real therapies to treat life-threatening illnesses like those mentioned at the outset of this teshuvah-then our answer would quite possibly change as well. In that case, we might well conclude that the need to derive the necessary stem cell material overrides our concern for the life of the embryo We might say this for two reasons: first, because there is no Jewish legal prohibition against the destruction of the embryo at any rate; and second, because the real prospect that this material would provide therapeutic benefit to an actual patient would easily qualify the therapy as pikuach nefesh. The matter requires further careful study, not only by this Committee, but by all who are concerned with Torah and its application to the fateful moral choices that we are called upon to make.
. In summary, we hope to have made the following points.
1. The practice of medicine is a mitzvah, partaking of the duty to save life. Because medicine is an experimental science, the mitzvah of medical practice includes medical research as well as the direct treatment of patients. For this reason, we are encouraged by the dramatic therapeutic prospects offered by research into human stem cells.
2. All human life, including prenatal human life, possesses an inherent sanctity that requires our respect and honor and that conflicts with the demand that we destroy it for our own purposes, even medical purposes.
3. The fetus is not a nefesh, a full legal person. Abortion is therefore permitted for reason of the life or health of the mother. It is not permitted in order to obtain fetal tissue for medical research. The tissue of fetuses that have been aborted for morally justifiable causes, however, may be utilized in that research.
4. The legal status of the embryo that exists outside the womb is inferior to that of the fetus. There is no duty to save it from death; nor is there an explicit prohibition against its destruction. For this reason, it is permissible to discard the excess embryos created as part of the procedure of in vitro fertilization and, by extension, to use them for purposes of stem cell research. If we may destroy some embryos in order to derive stem cells for the sake of that research, it is certainly permissible for scientists to make use of the already existing lines of stem cells in possession of scientists.
5. It is not permissible to create embryonic human life for the purpose of destroying it in medical experimentation. It might be permissible, however, to create and destroy embryonic human life in order to derive stem cell material that would be used as medical therapy for actual patients. The development of such therapies, if it ever occurs, lies in the distant future. In the meantime, it is incumbent upon all of us to continue to study, consider, and debate the moral implications of this promising new avenue of medical research.
Bava Kama 85a, a midrash on the words rapo yirapei.
, ed. H.D. Chavel (Jerusalem: Mosad Harav Kook, 1964), 41-42.
and Shulchan Arukh, Yore De`ah 336:1.
Yore De`ah 336:1.
. Nidah 5:3; Yad, Rotzeach 2:6.
. Ohalot 7:6. Some texts, including the printed version of BT Sanhedrin 72b and Rashi ad loc., read rosho ("its head") in place of rubo ("the major part of it").
, Rotzeach 1:9. On the law of the rodef, which the Rabbis derive from Leviticus 19:16 ("do not stand idly by the blood of your fellow"), see M. Sanhedrin 8:7 and BT Sanhedrin 73a.
Sanhedrin 72b, s.v. yatza rosho.
Yoma 85b and Shabbat 151b, on the verse "the Israelites shall keep the Sabbath...throughout their generations as an everlasting covenant" (Exodus 31:16). The Talmudic references apply this midrash to persons (i.e., nefashot) and not to a fetus in utero. The extension of the rule "we violate one Sabbath on its behalf" is Ramban's innovation; see Torat Ha`adam, 29.
, no. 16, p. 27.
, no. 5755.13; Contemporary American Reform Responsa, no. 16; American Reform Responsa, no. 171.
, no. 5755.13, end.
, no. 82; Rabbi's Manual (New York: CCAR, 1987), 247.
Yevamot 69b. We should note that this designation is made by the halakhah in accordance with its own categories and frames of reference. It is not a scientific designation, i.e., it is not based upon scientific observation as we understand that term today.
If needed, please consult Abbreviations used in CCAR Responsa.