mThough the Biblical mixed species law of kilayim is treated as a mathematical puzzle in recent daf yomi (Shab 84b-85), kilayim is also invoked in Jewish bioethics on genetic engineering. The kilayim law prohibits the planting and breeding of mixed species together. Kilayim has been used to argue against genetic engineering and, in particular, against genetically modified foods. The arguments against genetic engineering cite the Biblical verses (Lev. 19:19 cp. Dt. 22:9-11) on kilayim and later rabbinic texts (e.g., Ibn Ezra). For instance:
How does this verse [Lev. 19:19] relate to transgenic foods -- foods produced by combining DNA between species that are naturally prevented from cross-breeding? If we interpret it in the manner of Ramban, it seems to bar such trans-species alterations. According to Ramban, each species represents a special force and tampering with their boundaries can cause unfathomable harm. Because he was only considering crosses through naturally permitted pathways (as in creating a mule), it's likely he would have regarded genetic transfers between species that are naturally prevented from crossbreeding as a far more severe violation of the divine order, since it breaks down more fundamental boundaries. Accordingly, in an approach such as his, both the manufacture and consumption of transgenic foods would be prohibited.
Jewish opposition to genetically modified foods also draws upon the le-mino principle of Rabbi. Samson Raphael Hirsch. R. Hirsch writes:
Regarding the Species as Divine Order…. You should not interfere with the natural order which you find fixed by God in His world for its ultimate good. You must, by respecting the boundaries of that order, guard yourself against allowing the free use and transformation of this world, which He has granted to you, to degenerate into a God-forgotten, world-destructive presumption. (Horeb #402)
Hirsch asserts that the kilayim rules mandate a policy of non-interference with the actual reproduction of species. These rules avoid disruption of the natural order and of the purity required for the existence of the species. They apply to all species. However, Hirsch believes that species are fixed, eternal and unchanging, scientific presuppositions which are not endorsed by all.
To date, Orthodox posqim have not found the mixed species (kilayim) ban as a persuasive analogue against genetic engineering. Among the reasons not to apply the kilayim as a halakhic analogy for genetic engineering, it is argued: (1) The Biblical concern with mixed species does not pertain directly to GMOs. Still, Rabbinic authorities disagree about the kilayim of plants in shedding light on genetic engineering methods that transfer genetic material across species. (2) Kilayim cannot be extended analogically because it is a khoq, an “irrational” law. (3) Furthermore, there is some concern that genetic materials falls under the exclusion of materials that are not visible or are too minute. (But see R. S.Z. Auerbach cited by Wolff). (4) Finally, starting with the Talmud, rabbis disagree about whether kilayim rules ought to apply to non-Jews.
For Jews who differentiate the ethics of genetic engineering from a strictly halakhic (Jewish law) decision, you might appreciate this warning Rabbi Hirsch: “Do not forget that God has summoned you to the task of serving the world and cultivating it protectingly, but not to enter destructively into this orderly course of development through your self-seeking. Do not forget this, and do not put the powers of a created being which have been designated for its own species to the use of sustaining another species.” (Horeb 408)
Links to texts about kilayim and genetic engineering:
Goldschmidt, E., and Maoz, A. (1999) "Genetic engineering in plants--scientific background and Halacha aspects." Assia 17: 50-65 (in Hebrew).
Druker, Steven. Are genetically engineered foods in accord with Jewish law?
A Jewish Perspective on Genetic Engineering by Rabbi Akiva Wolff.