Genetic Engineering in Halacha – Part 2 by Ariel Caplan



Last week, we explained how genetic engineering involves the manipulation of the genetic code of an organism to induce a change in the structure, appearance, or functioning of the organism. We also described details of the Kilayim prohibitions, particularly those against crossbreeding animals and mixing plants. This week, we will examine approaches of contemporary Poskim as to whether genetic engineering violates any of the Kilayim prohibitions.

Does Halacha Acknowledge Microscopic Entities?

In an essay on genetic engineering and Halacha, Rav Dr. Carl Feit suggests that genetically modified foods should not be considered modified in Halachic contexts because the change is carried out through alteration of DNA, which is too small to be seen by the naked eye. This principle of ignoring that which cannot be readily seen has its basis in various Acharonim, including Aruch HaShulchan (Yoreh De’ah 84:36), who states that while there is no specific permission to ingest bacteria, their ubiquitous presence (including on food and in air) does not forbid eating or breathing. If Rav Dr. Feit’s approach were accepted, it would end the debate, as a Halachically insignificant action would certainly not violate any prohibition.

However, this approach is directly rejected by Rav Shlomo Zalman Auerbach in Minchat Shlomo Tinyana (97:27) and Rav Yehoshua Neuwirth (quoted in Nishmat Avraham, English edition, vol.3 p.300), and other Poskim who address the permissibility of genetic engineering imply their rejection by admitting that the question exists. Rav Shlomo Zalman argues that one is actively involved in the genetic transfer, and this involvement is enough to make the transfer Halachically significant. Rav Neuwirth adds that the results of genetic modification are (often) visible, unlike the microbial presence in food, which goes unnoticed. Either way, the point seems to be that we can ignore microscopic entities only so long as we ignore them – that is, provided we do not deal with them directly and cannot perceive their impact. However, if we involve ourselves in the microscopic world, we have no choice but to acknowledge the presence of microscopic entities and deal with them on Halachic grounds.

The Chazon Ish’s Approach – Potential for Life

Among the first Poskim to address genetic engineering was the Chazon Ish in his work on Seder Zera’im. He writes (Kilayim 2:16) that if one places sap from one tree into a groove in another tree from a different species, and a branch grows from that spot (presumably derived from cells within the transferred sap, as noted by Rav Mordechai Halperin), this constitutes a violation of the prohibition of grafting. He explains further that “There is…no difference between solid and liquid, and since sap has power to reproduce, it is considered grafting… Regarding twigs, each and every bit is a creature as long as it is fit for grafting and growing; hence, even sap is a complete creature.” Apparently, Chazon Ish believes that any piece of a plant which can be grown into a new plant under the right conditions is considered enough of an independent entity to carry a prohibition of grafting.

Regarding crossbreeding animals, however, Chazon Ish takes a very different tack. He writes that artificial insemination is completely permitted, as actual mating is the only act prohibited as Kilayim of animals. It is clear from this ruling that transferring genes between animals would not constitute a violation of Kilayim, as no action of mating is involved.

In two articles written about genetic engineering, Rav Mordechai Halperin (in one article) and Prof. Eliezer Goldschmidt and Dr. Arie Maoz (in the other) explain that in the context of plants, Chazon Ish requires a complete cell to be transferred for any Kilayim prohibition to be violated. (This is based on the fact that a single plant cell can be grown, under appropriate conditions, into a complete plant, hence fulfilling Chazon Ish’s description of something “fit for grafting and growing.”) It follows that transferring a single gene or a set of genes would be permitted.

Assuming that a complete cell is indeed required, Rav Halperin extends the Chazon Ish to allow cross-pollination between species, which results in the union of male gametes of the pollen-donating species with female gametes of the receiving species. This would generate hybrid plants. Rav Halperin explains that male gametes contain only half of the chromosomes necessary for a fully functional plant cell, and their only function is to unite with female gametes. Male gametes cannot be grown, even under laboratory conditions, into complete plants. Hence, they would not fall into the category of independently growing cells.

Action vs. Result – the Distinction of Rav Shlomo Zalman Auerbach

In a letter written to Dr. Abraham S. Abraham (quoted in Nishmat Avraham, Hebrew edition, 2007 printing, vol.4 p.182 and reprinted more fully in Minchat Shlomo Tinyana 97:27), Rav Shlomo Zalman Auerbach draws a somewhat different, more fundamental distinction. He addresses the question of injecting cells in a tree with tomato DNA, prompting it to grow a tomato where fruit should be. Rav Shlomo Zalman states that this would be prohibited, while transferring genetic material between animals would be permitted. The difference stems from the language used in the Pasuk in VaYikra 19:19: “Do not breed your animal as Kilayim, do not plant your field as Kilayim.” Rav Shlomo Zalman notes that the Torah focuses on the animals in the context of Kilayim of animals, whereas regarding Kilayim of plants the Torah focuses on the field itself being sown with multiple species. Hence, he concludes that only the union of two separate animal bodies would constitute a violation of Kilayim of animals, while Kilayim of plants is violated wherever a field is planted with two species. To frame the distinction in more conceptual terms, we might state that Kilayim of animals is defined by the action of mating two animals, while Kilayim of plants is defined by the result of two species planted in the same location.

Like the Chazon Ish, Rav Shlomo Zalman clearly permits genetic engineering of animals. Regarding plants, however, a significant distinction emerges. The Chazon Ish  states only that the union of distinct cells constitutes grafting. Rav Shlomo Zalman adds that a mixture of DNA within cells of one plant constitutes a violation of Kilayim. However, it is not clear if any amount would constitute a violation of Kilayim of animals or if there is some specific threshold that must be passed for the transferred genetic material to be significant.

Contradictory Pesakim of Rav Shlomo Zalman

Several individuals have noted an apparent contradiction between this ruling of Rav Shlomo Zalman and another ruling cited in his name in Sefer Kashrut Arba’at HaMinim. In this Sefer, Rav Shlomo Zalman’s nephew Rav Yechiel Michel Stern discusses an Etrog grown from a flower that was fertilized by pollen from a lemon tree. He quotes Rav Shlomo Zalman as having told him that this Etrog is not considered to have been grafted. (Thus, whereas a grafted Etrog is unfit for use in the Mitzvah of Arba’ah Minim on Sukkot, this Etrog would be valid for the Mitzvah.) Rav Stern explains that grafting requires material from multiple species, each of which could grow on its own, to the point where if each was placed in the ground, it would grow into an independent tree. It follows that a pollen grain, which cannot bring forth a plant on its own, is not considered a separate species.

This idea seems difficult to reconcile with the previously quoted ruling of Rav Shlomo Zalman that a transfer of genetic material alone would constitute a violation of Kilayim. Indeed, some treat the two statements as irreconcilable. Rav J. David Bleich notes the contradiction and leaves it unanswered. Prof. Eliezer Goldschmidt and Dr. Arie Maoz also mention the difference but offer no resolution; they imply that the ruling regarding tomatoes on trees supplants his ruling about Etrogim, which seems to have come earlier (and was transmitted orally rather than in writing).

Dr. Abraham S. Abraham, however, assumes that the two statements are not contradictory. He suggests that the distinction between the two lies in the fact that the Etrog that emerges from this cross-pollination will still essentially retain the properties of an Etrog, except that it will be somewhat nicer. However, a tomato growing on a tree constitutes a clear and apparent variance from the natural state of the tree, and we may therefore logically treat it as a distinct entity that would be subject to the prohibition of grafting.

Rav Shaul Yisraeli’s Approach – Requiring Two Separate Entities

In a responsum written to Rav Yoel Friedman, Rav Shaul Yisraeli severely limits applications of Kilayim of plants. In permitting cross-pollination of plants, he writes, “We have not found any prohibition of grafting except in that which is similar to and learned from mating [of animals]…and this happens only when one makes the connection with the body of the tree.” He concludes, “We have only that which the Torah prohibited, and hybridization was not included in [the Torah prohibition].” Apparently, Rav Yisraeli believes that the prohibition of grafting is limited to bringing together two completely separate entities.

Technical Arguments for Leniency

Prof. Eliezer Goldschmidt and Dr. Arie Maoz point out that certain aspects of the process of genetic duplication and introduction create degrees of separation between the donor plant and the recipient. First, the original extracted DNA is not put directly into the plant; rather, it is copied many times over through a process called PCR (Polymerase Chain Reaction), which compiles nucleic acids into new strands of DNA that are exact copies of the original strand. The original strand plus millions of copies are then inserted into the recipient plant. If the nucleic acids used as copying material are derived from non-plant sources, we might decide that their introduction does not constitute a mixing of plant materials.

Second, there is an additional step in the transfer of DNA in many cases, namely bacteria or viruses which are induced to incorporate the new genetic material and then are allowed to infect the plant. We might therefore consider the genetic material to have been absorbed by the bacteria or virus and considered of viral or bacterial origin rather than plant origin.


Until now, we have examined the question of whether Jews would be permitted to engage in activities of genetic engineering. Would the prohibitions of Kilayim impact Nochri involvement in this sphere?

Sanhedrin 56b records a prohibition for Nochrim to engage in crossbreeding of animals and grafting. This ruling is codified in Rambam (Hilchot Melachim 10:6). Hence, if any aspect of genetic engineering includes grafting, it should be prohibited for a Nochri as well. While this question may not initially appear very significant due to the small number of non-Jews interested in Halacha, it is actually a critical issue, as it should influence public policy of Jews and Jewish organizations whose statements carry influence in the public sphere.

To understand why, in this area, we should press for observance among Nochrim of those Halachot which apply to them, a certain perspective is necessary. If genetic engineering is considered a form of grafting, this indicates that it is subject to the universal moral restraint which the Halacha places on man’s creative activity, and thus should apply to Jew and Nochri alike. (The same might be said about other areas of Halacha which apply to Nochrim, mainly the Seven Noahide Laws. As advocates of universal ethical and moral standards, we look to the Halacha as our guide in understanding what constitutes a universally applicable ethic.)


Based on our original study of the facts of genetic engineering and the Halachot of Kilayim, we have seen various perspectives on whether genetic engineering would constitute a violation of the Kilayim prohibitions. It is clear that genetically engineering animals would not violate any prohibition. Transferring genetic material from one plant to another would not seem to pose a problem of grafting, as per the rulings of Chazon Ish, Rav Shlomo Zalman Auerbach (in Sefer Kashrut Arba’at HaMinim), and Rav Shaul Yisraeli. However, Rav Shlomo Zalman’s comments in his letter to Dr. Abraham S. Abraham seem to prohibit such an endeavor if it results in a dramatic and visible change (in accordance with Dr. Abraham’s interpretation) or even unconditionally (unlike Dr. Abraham’s interpretation).

Since the potential problem is one of grafting, a prohibition on genetic engineering of plants would follow the rules of grafting, as detailed last week.  Hence, genetic engineering of plants would be forbidden equally in Eretz Yisrael and Chutz LaAretz.  It would also apply to all plant species, whether they bear fruit or not.

Next week, we will address Torah perspectives on the ethical questions involved in genetic engineering.

Genetic Engineering in Halacha – Part 3 by Ariel Caplan

Genetic Engineering in Halacha – Part 1 by Ariel Caplan