Ask the rabbi: Individuality and the law

Does Halacha permit the medical separation of conjoined twins?

Sudanese conjoined twins (photo credit: Reuters)
Sudanese conjoined twins
(photo credit: Reuters)
Newspaper headlines periodically report ethical dilemmas and legal battles regarding the separation of conjoined twins. Estimates of the total incidence of conjoined twins, who may be conjoined in a variety of manners, range from 1 in 50,000 to 1 in 100,000 births, with a significant majority being stillborn or dying within 24 hours of birth.
Historically, the most famous twins were Chang and Eng Bunker of Siam (hence the colloquial term Siamese twins), participants in P.T. Barnum’s exhibitions, who were connected at the sternum but had separate limbs and organs. They lived active lives until the age of 63, and fathered many children by rotating weeks with their respective wives.
Medical advances would allow doctors today to separate similarly connected twins. Yet most twins possess more complex interdependency of organs and limbs, making them more difficult to separate, with one sibling frequently dying. An additional moral complication occurs when the siblings do not equally contribute essential resources, with weaker siblings considered “parasitic” since they utterly depend on their twins.
A central initial question is whether conjoined twins should be treated as one or two identities. The Talmud relates that Rabbi Yehuda Hanassi was asked on which head one should place tefillin on a conjoined twin (Menahot 37a). He took the question more seriously after a second person asked whether the father of a two-headed firstborn had to treat his offspring as one or two children for the purposes of pidyon haben (ritual redemption of the firstborn). Yet the Talmud notes that this question has its own unique considerations, leaving unanswered the larger dilemma of identity and its implications for other legal matters, such as inheritance.
The medieval Tosafist commentators, after confessing ignorance of this medical phenomenon, quote a midrash in which King Solomon poured boiling water on one head, and upon seeing the second head scream in pain, ruled that the two heads share one identity (Shita Mekubetzet). Since contemporary conjoined twins do not share such reactions, displaying distinct personalities and nervous systems, Jewish law treats conjoined twins as separate individuals. Rabbi Ya’acov Reischer (18th century) further noted that according to one talmudic account, Adam and Eve were created simultaneously as conjoined individuals and only later separated (Eruvin 18a). As separate individuals, conjoined twins cannot legally marry, since the other sibling may not share a bed with the spouse of his twin (Shvut Ya’acov 1:4).
This legal determination of separate identities creates quandaries regarding surgical separation, as it frequently leads to the death of one sibling. In some circumstances, untreated twins can continue to survive, but in many cases, inaction will lead to the death of both, especially when shared organs cannot support them.
In 1977, an Orthodox couple from Lakewood, New Jersey, agonized whether to separate conjoined twins who shared organs, including a six-chambered heart, thereby killing the weaker but giving the stronger twin a chance to survive. While their physician, C. Everett Koop (later to become US surgeon general), received permission from Philadelphia legal authorities to separate the siblings, the operation only proceeded following the oral directive of Rabbi Moshe Feinstein.
His reasoning, as recorded by his son-in-law Rabbi Moshe Tendler, noted that we generally do not sacrifice one life to save another. Yet Jewish law permits the killing of a fetus when it endangers its mother, deeming it a rodef (attacking pursuer) that threatens its carrier, upon whom it is utterly dependent (Sanhedrin 72). Rabbi Feinstein contended that analogously, since there was no way to save the first baby, which would have already died in utero without the support of the endangered stronger twin, one may kill the first twin. Rabbi Mordechai Halperin contends that one may similarly operate in comparable circumstances of asymmetric conjoined twins, including the controversial 2000 case of British conjoined twins who were separated against the wishes of their parents (Assia IV:1).
However, as Rabbi J. David Bleich noted, other scholars believe that the analogy to a rodef is inappropriate (Tradition 31:1, 34:4). Firstly, since both twins compete for the same contested resources, this is a case of mutual pursuit, under which Jewish law does not mandate third-party intervention (Rabbi Akiva Eiger, Ketubot 33a). Moreover, since the weaker sibling is definitively alive and has no malignant intentions, the case is more analogous to an innocent newborn child who has already emerged from the womb of its endangered mother. In that case, the Talmud declared, the child is not a rodef, since the mother is being “pursued by heaven,” and, as Maimonides tragically added, “This is the natural course of the world” (Rotzeah 1:9).
This remains an ongoing dispute, with scholars ultimately debating whether humans can choose between lives or must leave such matters in God’s hands.

The writer, online editor of Tradition and its blog, Text & Texture (, teaches at Yeshivat Hakotel.