For several hundred years, beginning in the fourteenth century, Spanish kings prohibited the breeding of mules, a practice that was thought to jeopardize the purity of Spanish horses. The Jesuit political philosopher Francisco Vitoria, lecturing in the first half of the sixteenth century, evidently found these prohibitions amusing and, in his discussions of the nature of law, made somewhat merciless fun of them: “Human laws derive in some way from the natural law. It is a natural law that the commonwealth be defended; from this derives the human law which prohibits mules.”
The prohibition does seem comical. Yet Diana Schaub, a member of the President’s Council on Bioethics, suggested in 2005 in a council meeting that the well-known ill temper of the mule might have its source in discontent with its betwixt and between status. Being a hybrid might not be so funny after all.
And indeed, recent news from the United Kingdom on the subject is anything but amusing. Last week, the British Parliament voted to allow the creation of “cytoplasmic hybrids,” which are being reported in the popular press as “part cow, part human.”
Even if one does not share Dr. Schaub’s general concerns about hybrids, one is likely to be very concerned about the creation of anything “part human.” Our respect for the barriers between species, and the profound differences between human beings and the other animals, seems to have taken a direct hit.
Moreover, other parts of the bill move us even further down the road toward “designer babies” than before. The bill permits the creation of so-called “savior siblings”¯children created through IVF who are tested to ensure that they are genetically compatible with older siblings who might need a tissue match for therapeutic purposes. These IVF children are certainly being treated as means and not ends in themselves.
These worries¯about the future of human nature and about the design of our children¯are real and profound. Unfortunately, they are not the most important part of the story here. Rather, what is central, and easily lost sight of amid the hype about anything interspecies, is twofold: first, that the procedure being used is really only a barely modified form of human cloning; and second, that the outcome , as in cloning, is a human embryo¯an individual human being at the earliest stages of his or her existence.
Some scientists will deny this on grounds that these embryos will never be implanted, and will thus never in fact grow to more mature stages of human existence. But these same scientists would not deny that these embryos, if they were implanted, would, if all went well, grow in the way characteristic of every other member of the human species¯first into a fetus, then into a newborn, then a child, an adolescent, and so on. These embryos are like any other member of the human species: They require a congenial environment in which to flourish, and, if denied that, they will die.
This only makes sense given the nature of the scientific process by which these “cytoplasmic hybrids” are created. The technique is a version of somatic cell nuclear transfer (SCNT), or cloning. In the “traditional” mode of SCNT, the nucleus of an ovum is removed and replaced with the nucleus of a “somatic” cell¯one containing the full genome of the species being cloned. Upon being electrically stimulated, the ovum’s cytoplasm reprograms the inserted DNA back to a totipotent, or an undifferentiated, state; the cell will now divide and develop as an embryo.
In interspecies SCNT, the only difference is that the ovum now comes from a member of a different species. So in human“bovine SCNT, human DNA is inserted into an enucleated cow ovum. But the genetic information that the embryo uses to pursue its developmental trajectory is entirely human. Otherwise, interspecies SCNT would not be all that desirable, since the stated purpose for this procedure is to provide embryos from which human embryonic stem cells can be derived. But, because researchers at the University of Newcastle, in England, found it difficult to persuade enough women to donate their eggs for cloning purposes, an end run was made around the egg problem by going to cow eggs, easily procured from abattoirs.
If one objects on principle to the cloning of human beings, one should then object to Britain’s endorsement of the creation of these cytoplasmic hybrids. Cloning has struck many as morally problematic because it seems to involve the manufacture of human beings. But human beings are persons, not things; they deserve to come to be as the fruit of parental love, expressed and made bodily in their physical embrace. Interspecies SCNT deviates even more from this normative pattern: The human beings who are created are made, not with the cooperation of one’s loving spouse, but by means of the technical joining of man and beast. Is it too old-fashioned to think that human beings ought not to beget with beings with which they can have no real reciprocity?
Even more important, if one holds that all human beings are worthy of full human respect, and that it is mere arbitrariness to withhold that respect on the grounds of an individual’s race, sex, or stage of development, then one should be aghast at what is being proposed in Newcastle and endorsed in the British Parliament. For that bill, and the work of the scientists at Newcastle, bring us all one further step toward the mass creation and destruction of human beings in their earliest stages of development. And this is, unlike quandaries over mules, no laughing matter.
Christopher Tollefsen is associate professor of philosophy at the University of South Carolina and co-author, with Robert P. George, of Embryo: A Defense of Human Life 
