In May 2016, scientists reached a new milestone — the culturing of human embryos to 14 days after fertilization.That experiment was stopped because of current international guidelines, but some scientists would now like policymakers to reconsider this rule.

Day 14 was originally chosen because it precedes formation of the primitive streak when cells begin to specialize in the process leading to neural development. It is also the last point of twinning, when one embryo can split into two, so some argue that prior to this point the embryo could potentially be more than one individual.

By creating a limit, policymakers confer a special status on the human embryo while still allowing for research and the pursuit of knowledge. Calls for an extension are understandable, but any change to the rule may be just as arbitrary as the 14-day mark. At what point does a fertilized egg warrant protections as a human subject? If response to pain is our measure, would administering anesthesia to the embryo satisfy concerns?

To develop a justifiable and thoughtful human embryo research guideline, we need a robust discussion that weighs moral and ethical concerns alongside potentially valuable medical knowledge.

The bottom line: Given the controversial nature of this work, knowledge for its own sake may not ultimately be an adequate justification for extending human embryo research, but now is the time for further debate.

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Updated 16 mins ago - Politics & Policy

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Illustration: Sarah Grillo/Axios

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President Trump returning to the White House from Minnesota on Sept. 18. Photo: Win McNamee/Getty Images

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Details: The suspect, a woman, was arrested while trying to enter New York from Canada, law enforcement forces said.

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Driving the news: Pennsylvania, which has 20 electoral votes, twice Wisconsin's number, actually has been trending higher in recent public and internal polling, a welcome development for the campaign.