Research was published earlier today in Nature and in Nature Cell Biology reports that human embryos have been kept alive outside the womb for up to 13 days, right to the edge of a “fourteen day/development of the primitive streak” rule enshrined in both guidelines and some nations’ laws.  And already three authors, Insoo Hyun, Amy Wilkerson, and Josephine Johnston,  have called, also in Nature, for “revisiting” that rule.  At Nature’s request I wrote a short piece giving my views on this issue; with its permission, I am reposting a slightly modified version of it here. Somewhat unusually, for me, I am not in favor of opening up more possible research, at least not now, based on what I currently understand.  For “why,” see below.

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When I was 8 years old my family drove to the Grand Canyon. At our last stop I begged my father to let us walk to the river: “It’s only a half hour away”. (I was probably off by about ten hours.) To get me back into our van, he promised me we would do that the very next time we went to the Grand Canyon. Oddly enough, in the next 37 years, he never took us back.

In the past few decades, bioscience has made several promises it couldn’t be called on. “No human germline engineering,” “no human reproductive cloning,” “no embryo research more than 14 day after fertilization.” None were possible at the time of the promises; all have started looking plausible in the last few years.

The latest is embryo research. It was easy to promise not to do research past 14 days (or the appearance of the primitive streak) because no one could keep ex vivo human embryos alive past at most nine days (usually seven).

But now two groups have kept human embryos alive on “in vitro implantation platforms” for 12 or 13 days. At least one of the groups destroyed its embryos to abide by the 14-day limit.

At the same time as the scientific publication comes a call to “revisit” this limit. Frankly, I am not convinced.

What is the benefit from keeping human embryos alive in vitro for extra days? It is said it can “lead to scientists being able to study all aspects of early human development with unprecedented precision.” Yet is an in vitro embryo attached to an “implantation platform” really a model for “early human development”? Who knows – and, perhaps more importantly, who can know barring unavailable detailed information about early embryos inside women’s wombs?

On the other side, if we do not use a 14 day rule, what limit will we use? Twelve weeks or so as in many European abortion laws? Viability (at around 23 weeks) as in U.S. abortion law? Human development is a seamless process, but ultimately lines need to be drawn even when – especially when – they do not naturally exist. I do not see a politically, or, for most people, morally acceptable line after 14 days. Given the questionable scientific value of the research, no case has been made for even revisiting the line, let alone changing it.

Hank Greely

Director, Stanford Center for Law and the Biosciences