The arrival of Zhong Zhong and Hua Hua, the world鈥檚 first cloned monkeys, has raised a lot of tricky questions. We address some of your biggest concerns here.
Is human cloning next?
No, but let鈥檚 look at this a little more closely.
In 2013, Shoukhrat Mitalipov at the Oregon Health and Science University and his colleagues听did, in fact, clone human embryos. They used a similar method to the one that created Dolly the sheep and this week鈥檚 cloned macaques. The team started with a fetal skin cell and fused it with an unfertilised human egg from which the nucleus had been removed. The use of viruses and an electric jolt triggered the embryo to start growing. In 2014, a team led by Robert Lanza at Astellas Global Regenerative Medicine in Marlborough, Massachusetts, did the same starting with skin cells from adult men.
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However, human embryos created in this way are not allowed to develop past 14 days, and certainly aren鈥檛 allowed to be placed into a surrogate. They are called 鈥渢herapeutic clones鈥� because they are used to create lines of stem cells that are genetically identical to the adult cell they are derived from. Researchers use them to learn more about human embryonic development and disease.
Human reproductive cloning 鈥� in which a cloned embryo is placed into a surrogate mother and allowed to grow to birth 鈥� is illegal in most countries. Even if someone did attempt it, it is unlikely to be a straightforward process.
Zhong Zhong and Hua Hua were created using fetal cells, and were the only live births after implantation of 79 embryos in 21 surrogate mothers. When the researchers attempted to use adult monkey cells, 181 embryos were implanted into 42 surrogates. Two live babies were delivered but they died soon after, one with developmental abnormalities.
This suggests that cloning adult cells 鈥� which would be needed to clone a living or dead human 鈥� remains a formidable technical challenge that would involve much wastage of donated eggs and a huge number of failed pregnancies.
Which all goes to say 鈥� and the scientific community is pretty unanimous on this 鈥� that the ethical, legal, philosophical and technical challenges make the cloning of a human a very unlikely proposition.
Why have primates proved so difficult to clone?
For reasons that are not fully understood, rewinding adult material back to the embryonic state needed to create a new individual has been more of a challenge in primates. 快猫短视频s have managed to clone 23 other species previously, although the reprogramming process has been somewhat hit-and-miss in other species too.
Could we clone even closer relatives, such as great apes?
This is currently out of the question, because research on great apes is either听banned or highly restricted听in most countries that have the technical capabilities to do so. The technical and scientific challenges would be formidable too, as we have already seen with macaques.听
Might it be possible to create a human clone assembled from cloned cells without having to go through normal development?
Again, no. 快猫短视频s are unravelling the secrets of disease and how the body works by creating and studying tiny 鈥渙rganoids鈥� of human organs and tissue, including听brains,听hearts听and听reproductive organs, but the idea of putting all of these together to create a whole person, is ludicrous.
Could you create a human clone without a brain that could supply spare organs, or be used for experimentation with new drugs?
Ethically, this is a complete no-no. But scientifically, it is hard to see how this would work. Genes that build the brain during pregnancy would have to be silenced in the embryo, and it is difficult to see how such a fetus could make it through pregnancy, let alone beyond. The brain is an important component of the body鈥檚 hormonal and electrical circuitry, and the brainstem controls important functions like breathing. It is unlikely a brainless body could be sustained or grow normally. There have been cases, however, of people surviving with听ultra-tiny brains, and听without the cerebellum.
Could you create cloned, pain-free, animals for scientists to experiment on?
It is theoretically possible if you could identify all of the genes involved in the pain process and either silence or mutate them in the embryo so that pain cannot be registered once the animal is born. But even if this was possible, the genetic modifications could impact other bodily functions in unexpected ways, and distort results by making the animal behave unnaturally 鈥� invalidating any experiments.
What about cloning highly endangered species before they go extinct?
This one could potentially be done. An endangered bison called a gaur was cloned two decades ago, but听died shortly after birth. A Brazilian conservation agency called听听proposed a听programme of cloning endangered species in 2012, but nothing appears to have come of it.
An attempt to clone endangered animals is apparently being made by a lab in South Korea founded by Woo Suk Hwang, the cloning scientist whose work on human cloned embryos in 2004 turned out to be fraudulent, but who has successfully cloned several animals, including the world鈥檚 first dog.
Hwang has听set up a programme to clone endangered animals, including Ethiopian wolves, Asian wild dogs called dholes and Siberian musk deer. But the biggest argument against this is that it would deflect effort and awareness away from addressing the major threats to all species, such as habitat destruction, logging, poaching and hunting. In addition, cloning endangered species would reduce the genetic diversity of the animals in the long run.
