An organism that contains cells from one or more species is called a chimera.

Now American and Chinese researchers have created embryos from monkeys containing human stem cells.

In a study published in the journal Cell, the researchers present how they injected human stem cells into monkey embryos and saw how they grew.

Three of the embryos lived up to 19 days after they were created.   

Will provide knowledge about embryo development 

The embryos were in petri dishes and there were no intentions to implant the embryos in a monkey's uterus.

What the researchers wanted was to understand the early development of embryos.

A monkey embryo with injected human stem cells.

Photo: Weizhi Ji / Kunming University of Science and Technology

Research on human and animal chimeras also aims to be able to create animal models in the future that will be used to understand diseases in humans and find new treatments.  

But the experiments have aroused controversy among various researchers who believe that the research is in an ethical gray area. 

- This research opens up Pandora's box to human and non-human chimeras.

These embryos were destroyed after 20 days, but it is only a matter of time before these chimeras will be fully developed, perhaps as a source of organ transplantation in humans, which is one of the long-term goals of this research, says Julian Savulescu, professor of medicine and bioethics at Oxford University.

Can make chimeras smarter with human cells 

He questions what the moral status of these beings is. 

- If in the future we produce pigs with human cells that function as organ donors, the human cells will be present in the whole pig's body, that includes the brain.

By modifying the brain, the pig's cognition can also be modified.

He points to an experiment in which human stem cells were injected into the brain of a mouse where they were multiplied.

The chimeric mouse developed better memory and learning ability.

- We do not know the capacity of a human-pig chimera.

Even if they look like a normal pig, their cognitive capacity may be affected.

In extreme cases, they could become human beings imprisoned in a non-human body.

Or they could have capabilities unknown to us humans. 

“Moral limbo” 

Anna Smajdor, associate professor of philosophy at the University of Oslo, also believes that these embryos, which partly contain human DNA, "float around in a moral limbo". 

- We treat animals differently than humans and we clearly know what the difference is between humans and animals.

But these chimeric organisms challenge the way we differentiate between animals and humans.

Since the organism has cells from both, should it then be partially protected because it partly contains human cells?

Or should we see it as fully human because it has human cells?

These questions, among other things, have not been answered, says Anna Smajdor. 

But Gert Helgesson, professor of medical ethics at Karolinska Institutet, does not agree that it is unethical, at least not at an embryonic stage.

He believes that there are often religious features in the criticism. 

- There are those who think it is wrong to cross species boundaries. They believe that there is a disrespect for the species. "We should not go in and tinker here with the cornerstones of life." But the question then is, why should we not do it? We have already done this many times, for example to get the desired properties in plants and animals. Maybe we need to tinker wildly for the next 50 years to save humanity. But then, of course, we must have our moral compass with us.