Amid a demand for experimentation on older human embryos, bioethicists in Europe are arguing for an extension of the “14-day rule,” which prohibits the use of embryos beyond that age.

In an article in the peer-reviewed journal EMBO Molecular Medicine, John Appleby of the University of Lancaster and his co-author Annelien Bredenoord of University Medical Center Utrecht write that the time has come to extend the 14-day rule to 28 days, reported Inverse, which covers technology, science and culture.

The 14-day rule, which is the law in nations that lead genetic research, including the United States and Britain, was established in 1985 after the birth of the first “test tube baby,” Louise Brown.

The rule is based on the premise that at that point, cells no longer simply copy and paste themselves. They begin to differentiate into three layers and become a unique individual, called “individuation.”

But Appleby and Bredenoord contend there are “both scientific and ethical reasons to extent the 14 day rule to for example 28 days.”

“Extending the window for embryo research to 28 days would allow scientists to reveal a new in-depth chapter of knowledge about the developmental processes that take place in embryos,” he wrote.

The authors argue that the tools are now available to manipulate human biology, allowing, for example, parents to pick and choose genes that could eliminate genetic diseases in their children.

But to do so, the authors insist, they need to know more about how those genes fare after the 14-day mark.

Critics argue that recent developments in stem-cell research make using the embryos unnecessary. The stem-cells allow scientists to create “synthetic” embryos that mimic early stages of human development.

Appleby and Bredenoord acknowledge that synthetic embryos are important research tools. But they maintain that extending the 14-day rule would allow them to develop them technology further and determine whether they really are useful alternatives to “real” human embryos.

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