Human embryo research has been conducted under strict time limits.  Known as the 14-day rule, work was permitted only until the primitive streak appeared signaling the embryo had reached a condition of true individuation (1).  At his point the embryos can no longer split into twins or fuse together.  While the rule has guided research, it only serves to provide a readily discernable marker of development and no clear consensus has ever been reached regarding the point at which human embryos acquire full moral status (1, 2).  New capacities to culture human embryos make it feasible for investigators to push past the 14-day limit, suggesting it was time to reconsider the long-standing rule (1).


The situation has grown far more urgent as it is clear that new and impending developments will turn the 14-day rule into a scientific anachronism (2).  In fact, what is coming in embryo research is so revolutionary that the old rules are no longer useful because these new entities may follow totally unnatural developmental patterns.  The 14-day rule will be meaningless for any new synthetic human entities which bypass a primitive streak stage now used as the time limit for experiments.  Scientists are on the verge of creating synthetic entities which function enough like human embryos to make them useful experimental tools.  However, it is not clear how to draw ethical use guidelines or devise effective time restrictions when new developmental stage bypass strategies seem likely to emerge (2).

A group of scientists at the forefront of synthetic entity embryo development is calling attention to the fast approaching dilemmas and urging colleagues to devise new guidelines before the crises materialize (2).  Recognizing any preemptive strategy based on developmental staging could soon be futile, they suggest setting limits based on features or capacities that are linked with the emergence of moral status.  They argue that regulatory limits based on first entry into situations raising moral concern will avoid any quandaries posed by technological developments enabling synthetic embryos to bypass normal developmental stages.

The notion of creating embryos that violate the cardinal, evolutionarily-conserved sequences of ontogeny is mind boggling.  What is next?  Artificial wombs (3, 4).  Keeping embryos alive for 13 days, far longer than normal without implantation, pushed the regulation-allowable limits to the extreme (3).  Investigators have signaled that work is proceeding to develop artificial womb technology to do things like resurrect woolly mammoths from extinction (4).     

Dom questions        

The 14-day rule was a compromise to allow human embryo research to go forward within defined boundaries and, although deemed successful, was not accepted unanimously (1, 2).  Rightfully seeking public dialog to set new limits, the creators of synthetic human embryo entities may face objections from groups disinclined to accept the notion that moral status accrues in a graded sequence of steps.  The general public will understand that new technologies able to supersede fundamental rules of biology will likely transgress many boundaries. 

(1) I. Hyun, A. Wilkerson and J. Johnston. 2016.  Embryology Policy: Revisit the 14-Day Rule.  Nature, 4 May 2016.

(2) J. Aach, J. Lunshof, E. Iyer and G. M. Church. 2017.  Addressing the Ethical Issues Raised by Synthetic Human Entities with Embryo-like Features.  eLife

(3). S. Knapton. 2016.  ‘Artificial Womb’ Breakthrough Sparks Row Over How Long Human Embryos Should be Kept in Lab.  The Telegraph, 4 May 2016.

(4) H. Devlin. 2017.  Woolly Mammoth on Verge of Resurrection, Scientists Reveal. The Guardian, 16 February 2017.