Roughly 50 years ago, scientists pursued a line of inquiry about the creation and development of human embryos in the lab. As of now, the extent of this research is limited to the first 14 days following fertilization — 14 days after one cell from mom joins one cell from dad to create a cell whose genetic composition has never before been seen in human history. 

This 14-day limit originates from a 1979 report produced by the Ethics Advisory Board of the U.S. Department of Health, Education, and Welfare. The report states that “it is acceptable from an ethical standpoint to undertake research involving human in vitro fertilization and embryo transfer provided that … no embryos will be sustained in vitro beyond the stage normally associated with the completion of implantation (14 days after fertilization).”

Recommended Stories

• Team Trump immortalizes the Jeffrey Epstein scandal
• Trump's tariff mania is anti-growth
• Iranian resistance groups need to show their cards

Since the report was published, researchers who studied these two-week-old human embryos discovered that 14 days is also about the time when a structure called the primitive streak forms inside the embryo. This structure delineates the central axis of the body, separating right from left. To quote the authors of a letter to the journal Nature advocating extending this 14-day limit, the choice of 14 days or the formation of the primitive streak (whichever occurs first, thank God), “was chosen as a pragmatic cut-off point.”

In the past few years, multiple influential academic societies and regulatory agencies have pushed for extending the 14-day limit on research with human embryos. In 2021, the International Society for Stem Cell Research removed the “culture of human embryos for research [past] … 14 days” from its list of prohibited research activities, partly because it may soon be technically feasible to keep them alive longer than 14 days. In 2024, the U.K.’s Human Fertilisation and Embryology Authority recommended that the current limit be doubled to 28 days — one month (i.e. one-third of the first trimester) spent undergoing experimentation in vitro — because scientific advances “have begun to push against the boundaries of the act” (the “act” presumably being the formation of human embryos in the lab).

In the previously mentioned letter to Nature supporting HFEA’s recommendation, the authors say that extending the limit to 28 days means that “researchers could learn more about crucial subsequent developmental stages and the processes that occur before neurons and sensations arise, such as the start of organ development and the formation of the placenta.” They also cite that the 28-day cutoff coincides with another “visual indicator,” this time the “closure of a structure along the embryo’s back called the neural tube; a different “pragmatic cut-off point.” 

As has been pointed out by others in this ethical debate, the shifting of the time at which embryo research should be prohibited to yet different “visual indicators” is a slippery slope. Why not use the emergence of the arm and leg buds at 32 days? Or the formation of eyelids at 41 days? Or the lengthening of the fingers and toes at 54 days?

Interestingly, the idea of a “slippery slope” was brought up in the report that proposed the original 14-day limit. It is worth noting that even those who oppose extending the 14-day limit still defend the 14-day limit as “the start of unique biological identity” (even though that identity was determined at conception on day 0) and maintain that the 14-day limit “makes sense.” The defenders of the 14-day limit say that “utilitarian objectives are limitless” when going beyond the 14-day limit (but, apparently, that the utilitarian objectives of the 14-day limit are acceptable).

To avoid this slippery slope and ethical issues altogether, I propose a different cutoff: zero days. After the fusion of sperm and egg, and the formation of a genome unique from every other genome that preceded it in history, no human embryos may be used for scientific research.

WISCONSIN SUPREME COURT STRIKES DOWN CENTURY-OLD ABORTION BAN

Does this mean that certain research questions about early human development will go unanswered? Of course. But research questions that deny the dignity of human life deserve to go unanswered. Any answers gained from denying antibiotics to black syphilis patients in Tuskegee, intentionally infecting prisoners from Stateville Penitentiary with malaria, or submerging Jews in icy water at Dachau weren’t worth gaining. 

The same goes for anything learned from experiments conducted on human embryos that might otherwise grow and thrive inside a mother’s womb, if they were ever given the chance.

Dr. William Mills is an assistant professor of biology at Mount St. Mary’s University in Emmitsburg, Maryland.