In my decade of teaching bioethics at Columbia University, I have always advocated for the application of five traditional guidelines to evaluate the ethics of an emerging biotechnology. These guidelines are: beneficence, maleficence, justice, autonomy, and respect for human dignity. Still, hovering in the back of my mind, there is another guideline to be considered called the “yuck factor.”

Originally termed by Dr. Arthur Caplan, the “yuck factor” was popularized by Dr. Leon Kass in 1997 when he described his position against cloning human beings. Dr. Kass defined the bioethical “yuck factor” as an intuitive response rather than a reasoned, ethical or moral violation by a new technology. Here is an extreme example: existing stem cell technologies could be used to create laboratory-cloned human hamburgers—something that would undoubtedly trigger the yuck factor. Of course there are no known research laboratories pursuing the cloning of human hamburgers, but many scientists are experimenting with cloning beef hamburgers.

The yuck factor also has been used to argue against other biotechnologies such as human-animal chimeras. Human stem cells could be theoretically transplanted into the fetus of an animal to reconstitute a human organ system in an animal model. Since the early studies to reconstitute a human immune system in mice, scientists have begun reconstituting human sperm and eggs or brain cells in mice. While many scientists understand the value of such animal models in studying gamete cell differentiation and neuroscience, few would actually ethically approve the use of human sperm produced in mice as a sperm source to generate a human embryo. Why? In large part, because of the yuck factor.

The technology that would be used to generate laboratory-cloned human meat for human consumption is similar to that used to clone  beef hamburgers; it involves harmlessly obtaining a small sample of muscle tissue from a living animal and isolating individual muscle stem cells called myosatellites. Myosatellites can reproduce fairly quickly in the laboratory and, when cultured under the appropriate in vitro culture conditions, fuse to form muscle fibers. Layered together, these strands of muscle cells and fibers form the essential components necessary to produce cultured edible meat.

Professor Mark Post of Maastricht University in the Netherlands created the world's first lab-grown cloned beef hamburger in 2013. Culinary experts tasted the hamburger and concluded that the hamburger tasted like real meat, although it was a little dry. The dryness was probably due to the lack of fat cells in the meat, since it is difficult to culture adipose cells together with muscle cells. Recent scientific innovations, such as the creation of artificial veins in synthetic organs, can improve the taste of cloned hamburger.

This first beef hamburger cost $350,000. Currently, the cost of the cloned beef has been reduced by 80 percent to $70,000. The commercial goal is to produce a five-ounce cloned hamburger for $10. There is even a cookbook containing 45 recipes using in vitro meat or cloned hamburgers as the main ingredient.

The advantages to producing cloned, animal-derived hamburgers include: a) creating a more sustainable option for meat production, b) eliminating animal waste, a significant source of land and water pollution, c) halting the livestock’s production of methane gas that is a significant source of global warming and d) producing healthier meat that is low in saturated fats and high in omega 3 fatty acids. Finally, cloned beef doesn't involve the slaughter of millions of cows and is a viable alternative to potential issue of animal cruelty.

Producing laboratory-cloned beef hamburgers triggers another interesting bioethical dilemma. Will a cloned beef hamburger be deemed Kosher or Halal certified by Jewish and Islamic scholars, respectively? Both Jewish and Islamic law requires ritual slaughtering before meat from a cow can be eaten. With cloned beef there is no need for animal slaughter. Moreover, if the cloned meat is derived from pig muscle, will these religious scholars permit or ban its consumption? The resolutions of these culturally-based ethical issues remain to be decided.

History has taught us several bioethical lessons that are pertinent to the ethics of cloned human meat. When the report of cloning Dolly, the sheep, appeared in 1997, there was considerable moral disdain in applying the technology to cloning human beings despite the natural precedent of identical twins being human clones. The tide of public opinion is now slowly changing regarding the application of cloning technology to human reproduction. A new Gallup poll released in 2016, found that 13 percent of Americans now say that it’s morally okay to clone human beings. The percentage of individuals who support human cloning is at its highest level in 15 years, and probably reflects the potential clinical applications of cloning to human infertility and to mitochondrial replacement therapy.

In fact, any new technology that presents a defined and necessary medical benefit has a high probability of eventually being ethically accepted, even if it initially elicits the yuck factor. That was true in the case of fecal transplants, which were first proposed to cure C. difficile infections. However, research emerging from fecal transplants in treating other diseases such as Crohn’s disease and ulcerative colitis has greatly improved our understanding of the role of microbiome in combatting a wide variety of diseases and subdued the relevance of the yuck factor.

There is no data, as yet, describing the potential medical, environmental, or nutritional benefits that ethically justifies the production and consumption of cloned human hamburgers. If such foods will have medical benefits, then the public may be more likely to accept their consumption.

Regarding ethical challenges associated with producing cloned human hamburgers, I am not concerned that the production of cloned human meat would lead society to embrace cannibalism along a slippery slope argument. Unlike generating cloned beef hamburgers, I strongly believe producing cloned human meat for human consumption indeed violates bioethics—not because of traditional guidelines or logical justification, but rather because of the yuck factor. This gut human reaction may not be logical, but is rooted in intuitive moral feelings. In the coming year when I teach bioethics to the next generation at Columbia College, I will present the yuck factor as a potential ethical guideline. I will hear my students’ reactions in applying moral intuitions to bioethics and whether they agree with my opinion that this lexicographical pearl should be included as an additional bioethical guideline.