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Jewish Perspectives on Genetic Engineering

Filed under: World Jewry
Publication: Jewish Environmental Studies

No. 2     Tishrei 5762 / October 2001

One of the technological marvels of the modern age is genetic engineering — the manipulation of genetic material, and the transference of genetic material between different types of organisms, to create transgenic or genetically-modified organisms (GMOs) with modified traits. The use of genetic engineering is advancing and expanding rapidly in many traditional fields including medicine and agriculture, as well as new fields such as biotechnology. Along with the rapid advances and expansion, there is a growing discussion and debate over the benefits and risks of genetic engineering and the difficult ethical questions raised by this new technology.

Among the real and expected benefits from genetic engineering are new medicines and medical procedures that can save and extend human lives, prevent or cure diseases, and repair cellular damage. Genetic engineering also promises to enable greater and more efficient agricultural production that can feed more people while using less pesticides and under more adverse conditions. Proponents of genetic engineering also speak of creating GMOs that will improve the quality of the environment through cleanup of oil spills and toxic wastes. Among the potential risks of genetic engineering are the creation of new disease organisms to which there is no natural resistance and no available cure, new food substances that create allergic or toxic reactions, and irreversible damage to natural ecosystems and the environment. Genetic engineering may be, according to its proponents, one of the greatest scientific advances in the history of mankind, or, according to its detractors, one of the greatest threats to the existence of life on the planet.

Man’s Relationship with the Natural World

How does the Jewish tradition relate to the modern phenomenon of genetic engineering? To answer this question, we need to first understand how Jewish tradition views nature and man’s interactions with the natural world. Jewish tradition takes a very positivistic view of the natural world, stressing how each progressive step in the creation of the natural world was “good” in the eyes of G-d the Creator.1 After the creation of man, with his free will and his ability to alter the creation, the Bible states that it was all “very good” in the eyes of G-d.2 Jewish tradition posits that man was created in the “image of G-d”3 to be a partner with G-d in mastering and perfecting himself and the natural world, as the following sources indicate:

  • The Bible commands man to “replenish the earth and subdue it and have dominion over the fish of the seas and over the birds of the air and over every living thing that moves on the earth,”4 indicating that man is commanded to have mastery over the natural world. The twelfth century commentator Nachmanides writes that God gave man the ability and the rulership over the earth to do according to man’s will with (all of the) animals, plants, and inanimate matter.5

  • In a midrashic story, Rabbi Akiva is challenged by the Roman general, Turnus Rufus, to defend the Jewish practice of circumcision, the apparent mutilation of a work of the Creator. Rabbi Akiva demonstrates to Turnus Rufus through the comparison of kernels of “natural” wheat with man-made bread, that the works of man, as finishing touches to nature, are better than the unfinished works of the Creator.6 Man is permitted, and sometimes commanded, to alter nature in order to perfect the works of the Creator.

While Jewish tradition assigns man the G-d-given right and even obligation to manipulate nature in order to bring benefit to man and the world, it also recognizes that man, through inappropriate use of his free will, can negatively interfere with the creation to the point of destroying himself and the natural world, as is expressed in the following midrash:

When G-d created the first Man he took him and showed him all the trees of the Garden of Eden and said to him “See my works, how beautiful and praiseworthy they are. And everything that I created, I created it for you. Be careful not to spoil or destroy my world — for if you do, there will be nobody after you to repair it.7

G-d placed limits on man’s activities to prevent man from negatively interfering with or destroying the creation. These limitations are both in the form of natural laws and in the form of religious laws. Examples of religious laws are the seven Noahide laws for all of mankind and the additional commandments to the Jewish people, such as “bal tashkhit” the prohibition against needless waste or destruction.

Therefore, we see that from a Jewish perspective, the natural world as created by G-d started out intrinsically “good.” Man was created by G-d and given the role of utilizing and perfecting the natural world, but within limits that would prevent him from destroying it.

Jewish Legal Perspectives

Where does genetic engineering fit in with the Jewish perspective on man and the natural world? Only recently has man learned how to circumvent the natural laws in order to manipulate and transfer genetic material between different species. The ethical implications of this newfound “freedom” will be discussed later. First, we will discuss the Jewish religious laws that are relevant to genetic engineering.

Genetic engineering can be divided into three main categories:

  1. Genetic engineering of humans — medical procedures which can save and prolong human life, enhance the quality of human life, or otherwise modify human characteristics.

  2. Genetic engineering of animals — procedures which can modify the characteristics of animals to allow greater productivity, improved nutrient content, increased disease resistance, and enhanced aesthetic qualities.

  3. Genetic engineering of plants — procedures which can modify the characteristics of plants to allow greater productivity, improved nutrient content, increased resistance to diseases, pests, or pesticides, and enhanced aesthetic qualities.

Genetic Engineering of Humans

Jewish law (halakhah) places supreme importance on pikuakh nefesh — the preservation of human life — which overrides all other commandments in the Torah except for murder, idolatry, or adultery.8 Therefore, the utilization of genetic engineering on humans in order to save or prolong human life is certainly permitted and may be required as long as the likely effectiveness of the procedure would justify the risks involved. Examples of this include procedures to remove, repair, or deactivate genetic defects; and procedures to increase resistance to disease or other stress. The usage of genetic engineering and, moreover, the usage of cloning on humans raises many ethical issues, particularly when this is done for non-life-preserving motives. These issues are very complex and are beyond the scope of this essay.9

Genetic Engineering of Animals and Plants

Genetic engineering of animals and plants in order to save or prolong human life would certainly be permitted, if not required, by halakhah. Examples of this may include genetically modified foods that increase the quality and quantity of the food supply, and genetically modified organisms that can clean up spills of hazardous wastes. On the other hand, some expressions of genetic engineering may threaten human life and health. Procedures which create a significant risk to human life and health — either directly or indirectly through their effect on the environment — may be prohibited by halakhah.

Aside from the above considerations, the two areas of halakhah most relevant to genetic engineering of animals and plants are kashrut (prohibited foods) and kilayim (prohibition of mixing different species of animals and plants). Relative to genetic engineering, these laws are only concerned with the transference of genetic material across species boundaries, not within the same species.


The kashrut laws delineate between species of animals which Jews are permitted to eat and those which are not permitted10 (all plants are considered kosher). When genetic material from non-kosher species of animals are mixed with kosher species of animals or with plants, does this render the receptor non-kosher? Most rabbinic authorities consider genetic material that is separated from or synthesized from the parent organism to be essentially “inert,” in other words, independent of the defining characteristics of the parent organism. Rabbi Eliyahu Bakshi-Doron, Chief Sephardic Rabbi of Israel, points out that, generally speaking, the genetic material that is transferred from non-kosher species is not considered “food,” has no taste, and is of negligible quantity relative to the permitted host species11 — all important factors negating the effects of the transferred material. According to most authorities, genetic material from non-kosher species is not itself non-kosher and does not render the new host organism non-kosher.

Another aspect of genetic engineering that relates to the kashrut laws involves changes to physical characteristics that are used to indicate the kosher status of certain mammals and marine animals. For example, only mammals that have split hooves and chew their cuds and only marine animals possessing both fins and scales are kosher. What if a non-kosher mammal such as a pig, which has split hooves, is genetically engineered to chew its cud? What if a catfish, which has no scales, is genetically engineered to grow scales? Both Rabbi S.R. Auerbach and Rabbi Bakshi-Doron discuss these complicated issues in their halakhic responsa.12


The biblical prohibition of kilayim, which forbids the mixing of different species of animals and plants, appears in Leviticus 19:19: “You shall keep my statutes. You shall not let your animal mate with a different species; you shall not sow your field with different species of plants.” The prohibition of kilayim, in general, applies only to the act of mixing different species and does not forbid deriving benefit from the products of this mixing (except for the prohibition on intermixing grapes with certain plant species where it is forbidden to derive benefit from the product as well). Furthermore, according to almost all rabbinic authorities, the prohibition of kilayim applies only to Jews and not to non-Jews.

Most rabbinic authorities rule that the prohibition of kilayim is restricted to the specific acts of interbreeding spelled out in Leviticus 19:19. Therefore, the non-sexual transfer of genetic material between different species of animals or between animals and plants is not within the legal bounds of the prohibition. The transfer of genetic material between different species of plants is less clear, and there is some disagreement among rabbinic authorities as to the permissibility of performing certain types of genetic engineering on plants. Many halakhic authorities take the position that there is no prohibition of kilayim in the genetic engineering of plants unless the material being transferred from one species to another has the ability, if planted in the ground, to grow a complete plant on its own — and this is seldom the case with genetic engineering.

E. Goldshmidt and A. Maoz,13 on the other hand, state that whereas in interbreeding of animals only the procreative act itself is forbidden, and therefore the non-sexual transfer of genetic material is permitted, some forms of transgenic engineering of plants may present a halakhic problem. Goldshmidt and Maoz cite Rabbi Avraham Karelitz and Rabbi S.Z. Auerbach, two major halakhic authorities of the twentieth century. According to Rabbi Karelitz, the transference of plant juices from one species of plant to another can be considered kilayim if the juices have the ability to cause new growth of the donor species in the receptor.14 Rabbi Auerbach similarly writes,

Whereas (genetic engineering) in animals…does not involve any prohibition of interbreeding, since the mixing is done only by means of the transfer of “material” from one species into another species of animal, regarding the grafting of trees it appears to be forbidden even if the mixing is done only by means of the injection of plant juices, which if planted in the ground would not sprout on its own; nevertheless, in the end the field is sown with two species.15

It should be noted that the genetic material from a donor species can be synthesized in the laboratory, which would probably avoid any halakhic problems cited above.

Another halakhic factor often introduced into the discussion on genetic engineering is the general principle that a prohibited substance has no halakhic consequence unless it can be seen with the unaided human eye or it causes a discernable effect. Since the transferred genetic material is only visible on a microscopic level, and since the effects are often not visible, some claim that this removes it from legal prohibition. Here, again, we find rabbinic disagreement. Rabbi S.Z. Auerbach writes that this exclusion does not apply in the case of genetic engineering since it is specifically this genetic material, however small, that we are interested in working with.16

In general, the Jewish legal decisors take a lenient position on genetic engineering. This is consistent with the general principle that anything not explicitly prohibited in the Bible and Talmud is assumed to be permitted. In the words of the early nineteenth century commentator Rabbi Yisrael Lifshutz, “Anything which we have no reason to prohibit is permitted, without having to find a reason for its permissibility. For the Torah does not mention every permissible thing, but rather only those things which are forbidden.”17 Rabbi Dr. Avraham Steinberg likewise writes, “As long as the act of perfecting the world does not violate halakhic prohibitions, or lead to results which would be halakhically prohibited, then we are given a mandate to use science and technology to improve the world.”18

Jewish Ethical Perspectives

Jewish ethical perspectives on genetic engineering are less clear than the legal perspectives. Genetic engineering crosses G-d-created boundaries that were until recently closed to mankind. Judaism gives man the ethical right to manipulate and change the natural world, but all of man’s actions must bring the world closer to perfection and not further away. There is still a great deal of uncertainty as to the effects (spiritual as well as physical) of genetic engineering on man and his environment, particularly in the long term. The extreme importance placed on the preservation of human life may require us to cross these boundaries. The ethical permissibility of genetic engineering for non-human-life-preserving (NHLP) purposes is less clear.

Does genetic engineering in NHLP situations violate the “spirit of the law” against mixing different species even if it does not violate the letter of the law? There is disagreement among the sages as to whether the rationale behind the laws against interbreeding are within the realm of human comprehension or not. The classical commentator Rashi writes that as hukim, these laws are “decrees of the King”19 and are beyond any human comprehension. If we cannot understand the reasons for these prohibitions, then perhaps the ethical scope of these laws can be limited to the specific cases given in the Torah, just as the legal scope was limited in the discussion above. Nachmanides, on the other hand, believes that humans are capable of understanding, at least partially, the reasons for these laws. Nachmanides writes that one who mixes two different species is “changing and denying the Divine Creation of the world,”20 a sin that may well go beyond the scope of the halakhic prohibition given in the Torah.

Supporters of Nachmanides’ position include the thirteenth century author of Sefer HaHinukh who writes on the prohibition of mixing species: “and all that G-d did is intended for the perfection of that which is needed in His world…and the species should not be mixed, lest it detract from the perfection and there will not be (G-d’s) blessing.”21 The eighteenth century German Rabbi Samson Raphael Hirsch writes in his commentary on the Bible:

[T]he Torah must consider this law (against mixing different species) which G-d implanted in the organic world of nature to be of the very highest importance for our human and Jewish calling, for it has interwoven consideration of it (the prohibition of mixing different species) in the whole of our life. Not only does it forbid us actual interference with this law by the prohibition of interbreeding animals and grafting trees, the unnatural crossing of species of plants and animals which are of different species in nature, but in our whole association with the organic world — in sowing and planting, in the use of animals for work, in using materials obtained from animal and vegetable sources for our clothes, and in the food we eat….It teaches us to keep such order that brings to our minds again and again the great law of “keeping species separate,” and its greater Lawgiver.22

Rabbi Levi Yitzchak Halperin, a contemporary rabbinic judge and Director of the Institute for Sci- ence and Halakhah, believes that, aside from cases where the Torah would clearly permit genetic engineering — for the preservation of human life and for enabling human procreation (for example, fertility treatments) — we should refrain from genetic engineering. While acknowledging that NHLP genetic engineering is permitted by Jewish law, Rabbi Halperin is concerned that we do not sufficiently understand what we are doing when we mix genetic material of different species and we could be causing unforeseeable damage to the good world that God created for us.23

Most contemporary Jewish authorities (rabbinic and otherwise) take a permissive but cautious position on NHLP genetic engineering. None of the major Jewish authorities have expressed blanket opposition to NHLP genetic engineering on either legal or ethical grounds. Rabbi Dr. Avraham Steinberg, an expert in Jewish medical ethics, believes that we should proceed with NHLP genetic engineering as long as we believe that the benefits to man outweigh the risks.24

Aside from the question of violating the spirit of the law against mixing different species, NHLP genetic engineering raises many other ethical and halakhic issues which require further research and discussion. For example:

  • How are we to determine which purposes justify the potential risks of genetic engineering, and what degree of certainty regarding the benefits and risks of genetic engineering are required in order to permit it on an ethical basis?

  • What if there is a reasonable certainty that a new genetically-modified (GM) food will harm a small number of people, but that it will also benefit a greater number of people? Related to this is the question of whether food manufacturers should be required to list all GM ingredients on their products — as is currently done in Europe but not in the U.S.

  • What if a new product may cause irreparable damage to certain plants or animals in the ecosystem in which it is released, but will also produce less expensive food, which will benefit consumers?


Judaism posits that the natural world, as created by G-d, started out as intrinsically good. Man was given the mandate to perfect himself and the natural world as a partner with the Creator. To fulfill his task, man may manipulate the creation, but only within certain limitations — these being defined by the natural and religious laws given by the Creator. The defining ethical criteria is that all of the legally permitted actions must bring the world closer to perfection and not further away. Genetic engineering is still a new technology with great promise and, some claim, significant risk to mankind. For the sake of preserving and enhancing human life, genetic engineering is generally encouraged by Jewish authorities, although there are reservations, and there are ethical issues in the genetic engineering of humans which are not covered in this article. Aside from situations where human life or health is at stake, the majority of rabbinic authorities rule that most forms of genetic engineering on animals and plants do not violate Jewish religious laws. There is disagreement as to the ethical permissibility of NHLP genetic engineering, although there seems to be little or no official objection. As genetic engineering continues to advance and spread, there is a great need for further research and discussion among Jewish authorities in order to address the halakhic and ethical issues.


Author’s Note: This article presents some general principles of Jewish law and ethics. For specific questions and direct application, please consult a qualified expert.



* The author wishes to acknowledge his gratitude to the following individuals for their assistance with this article: Rabbi Levi Yitzchak Halperin, Dr. Arie Maoz, Rabbi Pinchas Rosenstein, Rabbi Arie Avraham Smadja, Dr. Avraham Steinberg, and Dr. Ari Zivotofsky.

1. Genesis 1:1-25.

2. Genesis 1:31.

3. Genesis 1:26-27.

4. Genesis 1:28.

5. Nachmanides commentary on Genesis 1:28.

6. Midrash Tanhuma, Tazriah 19.

7. Koheles Raba 7:13.

8. See Talmud Bavli Shabbos 132a; Yoma 85b; Shulhan Arukh Orakh Hayim 328.1.

9. For further discussion on human cloning, see B’Or Ha’Torah, vol. 12 (5761/2001) (English).

10. Leviticus 11:1-47.

11. Binyan Av, section 4, siman 43, question 2.

12. Binyan Av, section 4, siman 43, question 3; Minhat Shlomo, section 2, siman 97, number 27.

13. E. Goldshmidt and A. Maoz, “Genetic Engineering in Plants — Scientific Background and Halachic Perspectives,” in Assia — articles, digests, and surveys in matters of halakhah and healing, 66-67 (September 1999):60 (Hebrew).

14. Chazon Ish, Hilchos Kilayim 2:16.

15. Minhat Shlomo, section 2, siman 97, number 27.

16. Ibid.

17. Tiferet Yisrael on Mishna, tractate Yadayim 4:3.

18. Quoted in B’Or Ha’Torah, vol. 12 (5761/2001) (English).

19. Rashi commentary on Leviticus 19:19.

20. Nachmanides commentary on Leviticus 19:19.

21. Sefer HaHinukh, mitzvah 62.

22. Rabbi Samson Raphael Hirsch commentary on Genesis.

23. Personal communication, May 2001.

24. Personal communication, July 2001.