The Scary World of Human Animal Chimeras


Imagine you are hospitalized and in critical condition. You need an organ transplant quickly, as the doctor has confirmed you cannot survive long without it. Unfortunately, no human donor can be found – but there’s still hope.

In the hospital backyard, or in a research institution not too far from your hospital bed, pigs and sheep have been implanted with human organs for just such an emergency situation as yours.

A pig or sheep is hastily killed and its organ harvested for your sake. You become the recipient of this ‘chimera’ or animal hybrid donor and you survive.

According to, chimeras, named after creatures from Greek mythology, are created artificially by combining genetic material from different species into a single embryo.

The adult animals that develop have different populations of cells that reflect different contributions from the species from which they were produced. Scientists have created the ‘geep’, for example, by combining genetic material from both a goat and a sheep.

Partially human hybrid embryos have been created by fusing human cells and animal eggs, and partially human chimeric embryos have been created by injecting human embryonic stem cells into animal embryos.

Most scientists want to produce such embryos only for research and oppose experiments that would allow human-animal chimeras to be brought to term.

Ronald Bailey in a recently published article stated that more than 120,000 Americans are currently on waiting lists for lifesaving organ transplants. Every day some 22 of them die before they can receive a transplant. Not surprisingly, though, valid questions have also had to be raised with respect to how ethical the organ-harvesting processes are.

At Stanford University, stem cell researcher Hiromitsu Nakauchi has made some significant steps toward growing human organs inside of animals.

Nakauchi is now working with Pablo Ross, a developmental biologist at the University of California, Davis, to create human-pig and human-sheep embryos to see if the technique can produce human organs.

Once the human-pig and human-sheep chimeric embryos are created, they are installed in the wombs of pigs and sheep, where they are allowed to gestate for 28 days before being removed for examination.

Normal gestation is 114 days for pigs and 152 for sheep. For now, they stop short of full gestation to avoid ethical controversy.

Last year, the National Institutes of Health (NIH) imposed a moratorium on funding any research in which human pluripotent cells are introduced into nonhuman animal embryos. But why would anyone object to this potentially lifesaving research?

“You’re getting into unsettling ground that I think is damaging to our sense of humanity,” the New York Medical College biologist Stuart Newman recently told In the same NPR report, Jason Robert, a bioethicist at Arizona State University, said, “One of the concerns that a lot of people have is that there’s something sacrosanct about what it means to be human expressed in our DNA.”

He added that some people might consider that inserting human DNA into “other animals and giving those other animals potentially some of the capacities of humans that this could be a kind of violation – a kind of, maybe, even playing God.”

One issue that worries folks like Newman and Robert is the possibility that human stem cells, instead of growing into transplantable hearts, kidneys or livers, might migrate to the brains of animals or to their reproductive organs. Would human neurons in the brains of pigs generate something like human consciousness?

Another concern cited by Bailey is even more chilling: If human stem cells grew into ovaries and testes, it might be possible for human-pig chimeras to mate and possibly give birth to a human child.

The simplest way to avoid this problem would be to make sure that any such chimeras never get close enough to one another to breed.

There have been other serious concerns as well. Iain Brassington in a report for the Medical Ethics blog, noted in late 2014 that although chimera organs are ‘personalized’ and unlikely to be rejected, one of the major concerns about using organs transplanted from animals is the risk of ‘zoonosis’ – the possibility that an animal virus might be transmitted along with the organ, resulting in a new disease that could cause a pandemic.

Brassington raised yet another worry about adding human stem cells to pig embryos: the resulting pigs might acquire human features. If a pig grew a human foot, it could be disconcerting.

But what if it showed signs of human self-awareness? The risk of this happening is even lower than the risk of zoonosis, but if it did, could we still confidently draw the line between humans and animals?

In the words of NIH ethicist David Resnik during the agency’s November meeting: “The specter of an intelligent mouse stuck in a laboratory somewhere screaming ‘I want to get out’ would be very troubling to people.”

In an article published in early 2016, Antonio Regalado made reference to some startling biotechnological developments. “We can make an animal without a heart. We have engineered pigs that lack skeletal muscles and blood vessels,” said Daniel Garry, a cardiologist who leads a chimera project at the University of Minnesota.

While such pigs aren’t viable, they can develop properly if a few cells are added from a normal pig embryo. Garry says he’s already melded two pigs in this way and recently won a $1.4 million grant from the U.S. Army, which funds some biomedical research, to try to grow human hearts in swine.

Regalado observed that the new line of research goes further because it involves placing human cells into an animal embryo at the very earliest stage when it is a sphere of just a dozen cells in a laboratory dish.

This process, called “embryo complementation,” is significant because the human cells can multiply, specialize, and potentially contribute to any part of the animal’s body as it develops.

In 2010, while working in Japan, stem cell researcher Hiromitsu Nakauchi used the embryo complementation method to show he could generate mice with a pancreas made entirely of rat cells. “If it works as it does in rodents,” he says, “we should be able to have a pig with a human organ.”

Other scientists find these possibilities unnerving. Pablo Ross, a veterinarian and developmental biologist at the University of California, Davis, where some of the animals are being housed queried: “What if the embryo that develops is mostly human? It’s something that we don’t expect, but no one has done this experiment, so we can’t rule it out,” he said.

Animal lovers have their concerns too. Alicia Kennedy for Good ( recently pointed out that the animals in which Ross’s team generates these organs will not survive; in essence, they’re turned into disposable organ factories, à la the nightmarish book/movie Never Let Me Go, in which human children are raised to grow organs for the rich.

Katherine Ripley for the Huffington Post recently reviewed some of the ethical concerns and noted: “…I think the real reason these experiments scare us is that they will force us to confront the question of what makes humans different from animals.

Bioethicist Jason Robert, who was interviewed by NPR, offered one possible answer: our humanness lies in our DNA. If that is the case, and you put human DNA in a non-human animal, you could blur that line between humans and other species.

And once you consider that possibility, you get into even scarier questions. Could you give a pig so many human characteristics that you can’t justify experimenting on it anymore?

Could you give it so many human characteristics that slaughtering it to give the pancreas inside it to a dying person would not be a sacrifice for the greater good, but rather, murder?

This is the reason that the NIH (National Institutes of Health) has forbid funding this research. They worry about the ethical consequences that could result from it. But I think you can take the concerns one step further, and ask what this research reveals about our current ethical standards.

If it is possible to combine the DNA of a human and the DNA of a pig into one creature, does that mean the pig was never really that different from a human? And if so, what right do we have to experiment on it?”

She concluded: “When we so frequently see evidence of emotion, communication, and even empathy in non-human animals, it becomes more difficult to justify our domination over them.

What gives us the power to designate pigs as the bearers of our organs? Will we acknowledge that their bodies are similar enough to ours to harbor our own beating hearts, while maintaining that their brains are different enough to justify slaughtering them?

And that leads into the final question: Do these experiments not only make pigs more human but also, perhaps, make humans less human?

The word “humane” is synonymous with compassionate and merciful, as if we humans are the only animals who have the mental capacity to treat other creatures justly and kindly.

Will we lose that quality if we continue to experiment on less powerful beings for our benefit? Or, have we already lost it?

There is a reason why God forbids sexual interaction between humans and animals; bestiality. And the aforementioned experiments come dangerously close to crossing that line.

Mankind is not ‘just another animal; another species’, as so many try to argue today. The Bible informs us that God created man “a little lower than the angels” (Psalm 8.5), not ‘a little higher than an animal’. And Gods commandment is that each should reproduce after his kind… and God saw that it was good.” (Genesis 1.24, 25).

Article Credit: Prophecy News Watch