Scientists make first human-monkey embryo

Monkey business: Human cells injected into macaque embryos survived for up to 20 days. © Getty

Are scientists opening a Pandora’s box? The latest breakthrough could make it possible to grow human organs inside animals. It will save lives, but the ethical implications are enormous.

In a plot twist straight out of Planet of the Apes, scientists confirmed last week they have created the world’s first human-monkey in a laboratory in China. The embryos were kept alive for only 20 days in petri dishes, but future experiments could produce organs for life-saving transplants.

The US-Chinese team injected human stem cells into 132 embryos of long-tailed macaques. These cells were modified to appear bright red so researchers could study their development. The principal investigator Tao Tan said what they saw was “amazing”: human cells multiplying and interacting with monkey cells.

Organisms with two sets of DNA are called chimeras. The same team, led by Juan Carlos Izpisua Belmonte, created the first human-pig chimera in 2017, but with limited success. Pig and human cells were simply too different. However, in macaques, “the human and monkey cells cooperate with each other in building the embryo”.

But why create a chimera in the first place? Belmonte hopes they will solve the global shortage in organ donations. In 1954, doctors accomplished a modern miracle when they carried out the first successful kidney transplant. But only 10% of patients worldwide receive a transplant and the organ shortage fuels the so-called red market in illegal body parts.

One solution is to take organs from animals in a procedure called xenotransplantation. In 1984, an American infant known as Baby Fae was given a transplanted baboon heart. She died 21 days later, her body’s immune response rejecting the foreign tissue. With any transplant, doctors try to match the donor’s and patient’s blood types and use drugs to suppress the immune system. This is even harder between species.

Chimeras could solve this problem, because they allow human organs to grow inside animals for transplants. This research is in its early stages, but bioethicist Julian Savulescu believes “it is only a matter of time” before science fiction becomes reality. This experiment, he says, opens a Pandora’s box of ethical questions we must face before it is too late.

The key issue is the moral status of these animals. What rights do they have? If chimeras become more like us than non-human animals, would it be ethical to harvest their organs for our benefit? Savulescu says we will have to assess their “mental capacities” to avoid the dystopian nightmare of creating an exploited second-class of humans.

Others argue chimeras are not necessary. Biologist Alfonso Martinez Arias says the experiments “do not work” and the alternatives are much more promising. For example, exciting research into 3D bioprinting and tissue engineering could lead to designer organs, with none of the ethical concerns. And the economist Alvin Roth thinks the solution is even simpler: change the current transplant system to encourage more people to donate.

So, are scientists opening a Pandora's box?

Frankenstein’s monkey

Some say yes, this is a monstrous idea. These scientists have clearly never seen any science fiction movie. The story will either end badly for the chimeras, who will live short miserable lives in organ farms so that we can extend ours a little longer. Or the chimeras will break free, reproduce in the wild and take revenge on their creators. We should not play God and meddle with nature.

Others say no, we shouldn’t confuse medical progress with science fiction. From hybrid fruit likes clementines to animal crosses like mules, humans have been engineering nature for millennia. Scientists are nowhere near making a race of superintelligent apes. The current research is about a small number of human cells in a laboratory that could help cure disease and save lives.

You Decide

  1. Would you accept a life-saving organ which was grown inside an animal?
  2. Should scientists be allowed to create chimeras for experiments?


  1. Create your own chimera, combining two or more animals to make a new species. Draw a picture to show what it looks like and list how it will change the world.
  2. Write a one-page story from the point of view of a human-animal chimera that escapes the laboratory where it was created.

Some People Say...

“Accursed creator! Why did you form a monster so hideous that even you turned from me in disgust?”

Mary Shelley ( 1797 – 1851), English author of Frankenstein

What do you think?

Q & A

What do we know?
It is generally agreed that chimeras are organisms containing at least two different sets of DNA. Besides laboratory experiments, there are other ways this can happen. Mothers and their children share a small number of identical cells exchanged during pregnancy. A more unusual case is Vanished Twin Syndrome, where one twin absorbs the other and is born with both sets of DNA. Chimeras should not be confused with hybrids, where two species are crossed through sexual reproduction.
What do we not know?
One main area of debate is where to draw the line between humans and animals. Most philosophical traditions argue that it is morally justifiable to kill an animal to save a human life. These human-monkey embryos contain up to 7% human cells, but at what point do they become human? Some argue our soul or mind separates us from animals, so does a monkey with a human brain also have a soul? Others argue that, since we share over 90% of our DNA with them, it is impossible to draw a line between us.

Word Watch

A small cluster of fertilised cells that will develop into a new organism. Research on human embryos is limited to the first 14 days of development but the exact point it becomes a living being is a hotly debated and highly emotional issue.
Stem cells
A special embryonic cell with the ability to develop into many different cells and repair damaged tissue. In 2006, researchers discovered how to reprogramme adult cells to become stem cells, overcoming ethical concerns surrounding embryo research.
In Greek mythology, the fire-breathing Chimera had the head of a lion, the body of a goat and a snake for a tail.
Red market
Iran is the only country where it is legal to sell organs. In the rest of the world, they are traded illegally by criminal gangs who exploit vulnerable and desperate groups.
Immune response
The body attacks the organ, treating the transplant like an invading virus.
Bioethics is the study of moral and philosophical questions arising from advances in biology and medicine.
Pandora’s box
In Greek mythology, a jar that, when opened, released sickness and death into the world.
For example, in Kazuo Ishiguro’s 2005 science fiction novel Never Let Me Go, self-aware clones discover their fate as organ donors.
3D bioprinting
Instead of ink and plastic, tissue engineering uses a “bio-ink” of living cells to make artificial tissue and organs.
Alvin Roth
The Nobel Prize-winning economist devised a “kidney exchange”, using economic theory to link up matching pairs of patients and donors.

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