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A team of scientists has created synthetic human embryos from stem cells, without the need for either an egg or sperm — a remarkable breakthrough that raises plenty of thorny ethical questions.

While these embryos only resemble ones in their earliest stages of development — they are still far from forming a brain or beating heart — the researchers are hoping to study how genetic disorders affect this process as well as the causes of recurrent miscarriages.

Still, the research has some serious ethical and legal implications, The Guardian reports, and it's currently illegal to implant synthetic embryos into a patient's womb.

The researchers aren't planning to grow these embryos beyond the internationally agreed-upon limit of 14 days, and it's still unclear if they'd even be able to mature beyond that stage anyway.

Team lead Magdalena Zernicka-Goetz, a biological engineering professor at the University of Cambridge told CNN the research has already been accepted into a reputable scientific journal.

But it hasn't been published just yet, meaning that many experts are waiting before they comment.

The cells were grown from human embryonic stem cells and were manipulated to develop cells that typically lead to the formation of a yolk sac, placenta, and the embryo itself.

"Our human model is the first three-lineage human embryo model that specifies amnion and germ cells, precursor cells of egg and sperm," Zernicka-Goetz told The Guardian. "It’s beautiful and created entirely from embryonic stem cells."

Given the extremely sensitive nature of the research, Zernicka-Goetz was measured in her statements to the media, but still stressed the importance of her work.

"I just wish to stress that they are not human embryos," she told CNN. "They are embryo models, but they are very exciting because they are very looking similar to human embryos and very important path towards discovery of why so many pregnancies fail, as the majority of the pregnancies fail around the time of the development at which we build these embryo-like structures."

Zernicka-Goetz and her team have previously shown that stem cells from mice could be coaxed into assembling themselves into early embryo-like structures, including the beginnings of a brain and beating heart.

At the time, experts called it a "new technological revolution," likening the research to "the birth of Dolly the sheep."

And her team's latest efforts are only the beginning of translating this concept into human models. Many challenges remain and even in the case of mice, these synthetic embryos have yet to be successfully grown into live animals inside the womb.

Even synthetic monkey embryos that were implanted into female monkeys in China didn't make it past a couple of days of pregnancy.

And then there's the question of regulating human-embryo research. Some experts argue these synthetic embryo models shouldn't be governed by the same laws as actual human embryos, but finding a consensus on the topic could take a while.

"These findings suggest that we would soon develop the technology to grow these cells beyond the 14-day limit, with potentially more insights to gain into human development," Ildem Akerman, a gene regulation researcher from the University of Birmingham, told the BBC.

"Nevertheless, the ability to do something does not justify doing it," she added.

More on embryos: Scientists Create Synthetic Mouse Embryos Without Sperm or Eggs

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