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17 Timepoints When a Human Life Begins: 2024 Version in the Wake of the Alabama Ruling

I wish that I could stop reposting this essay – I do so whenever limitations on women’s reproductive rights become ever more egregious. And that certainly happened when the Supreme Court of Alabama ruled on February 16 that human embryos, even those in the suspended development of a deep freeze, are “children” under the state’s Wrongful Death of a Minor Act.

I wrote this essay in 2013, in response to common confusion of “embryo” and “fetus” – never imagining the blurring would extend to “baby”. We scientists are sticklers for precision and accuracy. Even physicians oversimplify human prenatal development, counting the weeks of pregnancy from the last menstrual period, two weeks before fertilization. That error has legal repercussions in so-called “heartbeat” laws claiming a deadline of 6 weeks for termination that, biologically speaking, really means 4 weeks.

“17 Timepoints” in 2013 apparently hit some nerves, for it’s been quoted, cited, excerpted, complimented, criticized, and tweeted. Various right-to-lifers in particular have trashed me, taking exception to my litany of biological facts.

In 2017, I reposted the essay in response to a document from the Department of Health and Human Services citing its role of “serving and protecting Americans at every stage of life, beginning at conception.” Oops.

I posted again in 2022, in the wake of Justice Alito’s leaked 98-page draft abortion opinion that would doom Roe v. Wade. So now, in some states, a woman in the throes of a miscarriage can be refused care at a hospital, and when the fetus becomes a dead baby in her home, she’s accused of murder. That’s what happened to Ohio resident Brittany Watts in January.

And now, ARTs – assisted reproductive technologies – have joined the discussion. Three couples have sued The Center for Reproductive Medicine and Mobile Infirmary Medical Center in Alabama because one of them accidentally dropped a vial containing a frozen embryo in the “cryogenic nursery” in response to “freeze-burned” skin. The unfortunate fumble happened in 2020; the suit filed in 2023.

The language of the lawsuit is telling.

The three couples are “parents,” the offspring “deceased embryo/minor,” and one in particular, “Baby Aysenne.” The legalese deems the “parents” “next friends,” which means that they represent another who cannot comment, such as the ball of cells that is a human blastocyst residing in a freezer.  

Because the embryos arose with the help of IVF, the immediate aftermath of the Alabama ruling was for some fertility clinics to halt the procedure, calling into question even the storing of frozen embryos. The rage has yet to subside.

But the meme equating an unfertilized chicken egg with a chicken suggests the need for another biology lesson. How many people are reposting variations on that theme without realizing the biological distinctions, and their relevance? So, here we go again, updated only slightly.

From October 3, 2013

I’m the author or co-author of nearly 40 editions of several college-level life science textbooks published by McGraw-Hill: general biology, human anatomy and physiology, and my favorite, now in its 14th edition, human genetics. All have had detailed chapters on human reproduction and development, including tracking the history of assisted reproductive technologies.

Life science textbooks from traditional publishers don’t explicitly state when life begins, because that is a question not only of biology, but of philosophy, politics, psychology, religion, technology, and emotions. Rather, textbooks list the characteristics of life, leaving interpretation to the reader. But I can see where the disingenuous idea comes from that textbooks define life as beginning at conception — it requires a leap off the page.

Consider a report from the Association of Pro-life Physicians. After a 5-point list of life’s characteristics from “a scientific textbook,” this group’s analysis concludes with “According to this elementary definition of life, life begins at fertilization, when a sperm unites with an oocyte.”

I’ve thought a great deal about the question of when a human life begins. So here are my selections of times at which a biologist might argue a human organism is alive. I’ll save my opinion for the end.

1. Life is a continuum. Gametes (sperm and oocyte) link generations.

2. The germline. As oocytes and sperm form, their imprints – epigenetic changes from the parents’ genomes – are lifted.

3. The fertilized ovum. Of the hundreds of sperm surviving the swim to the oocyte, one jettisons its tail and nuzzles inside the much larger cell, which becomes a fertilized ovum. That’s conception.

4. Pronuclei merge. The DNA in these packets from each gamete replicate, and then the pronuclei meet and merge, within 12 hours. The intermingling chromosomes form a new human genome. Following the first mitotic division, the information present in the DNA sequences of some genes from the new genome are accessed to make proteins. But maternal genetic information, in the form of messenger RNA “transcripts,” still guides development.

5. Cleavage divisions ensue. The cells of an 8-celled embryo (day 3) have not yet committed to becoming part of the embryo “proper” (one with layers) or the supportive membranes. Such a cell can still, on its own, develop. Sometimes that happens, and multiples result.

6. Day 5. The new genome takes over as maternal transcripts are degraded, their parts recycled. Cells continue to divide, forming a hollow ball. A smidgeon of cells, the inner cell mass (icm), that separates and lodges on the interior surface will become the “embryo proper,” as the hollow ball contorts into the extra-embryonic membranes. (The icm is what all the fuss about human embryonic stem cells is about — but the stem cells arise in a glass dish, they don’t actually come from an embryo, never have.)

7. End of the first week. The embryo implants in the uterine lining.

8. Day 15. The primitive streak forms. This marking along one side is the first inkling of a nervous system. Some nations ban experimenting on human embryos from this point.

9. The gastrula forms throughout week 3. Tissue layers arise, first the ectoderm and endoderm, then the sandwich filling, the mesoderm. Each layer eventually becomes specific body parts.

10. Day 18. The heart beats.

11. Day 28. A strip along the back of the embryo, the notochord, closes. Within it forms the neural tube, which gives rise to the spinal cord; a bulge at the top comes to contain the brain. If the tube doesn’t close completely, a neural tube defect results.

12. End of week 8. The embryo becomes a fetus, all structures present in rudimentary form.

13. Week 14 or thereabouts. “Quickening,” the flutter a woman feels that will progress to squirms and kicks from within.

14. Week 21. A fetus has a (very slim) chance of becoming a premature baby if delivered. This is the earliest point of viability. Obstetricians call this week 23.

15. Birth.

16. Puberty. Sexual maturity is the Darwinian definition of what matters to populations and species, when reproduction becomes possible.

17. Social milestones. Acceptance into (a) preschool (b) college or (c) medical school; marriage; a career begins; when grown offspring leave home.

My answer? #14. The ability to survive outside the body of another sets a practical, technological limit on defining when a sustainable human life begins. That limit may of course change. (Meanwhile, a February 27, 2024 BBC report, Global Perspectives on the Alabama Ruling, IVF and When Cells Become a Person, quoted the italicized sentence from 2013.)

Having a functional genome, tissue layers, a notochord, a beating heart … none of these matter if the organism cannot survive where humans naturally survive.

Technology has taken us to the ends of the prenatal spectrum, yet not provided too much for the middle, other than fetal surgeries for a handful of conditions and attempts at mimicking a uterus. We can collect and select gametes to guide conception, collect and select very early embryos to avoid those genetically destined to a terrible medical fate.

Although the gestational age at which a premature infant can survive has crept ever younger, it hasn’t by much, not since I starting thinking about these things back when I was a stage #16. In high school I worked in a lab that processed material that would arrive in dixie-cup-like containers, the “products of conception” after abortions, which was legal in New York state. The cups held floating tiny tissue pieces, nothing like the brutal images on the placards held up in front of Planned Parenthood clinics to antagonize women making the hardest choice of a lifetime.

I would really love to retire this post. I can’t bear to read the entire Supreme Court of Alabama decision, after having read excerpts that cite the bible – hardly a document of expertise on human prenatal development – for I fear my head might explode. Religion, with its reliance on belief and not facts and the tendency to speak for all others, should never trump biology in making decisions that affect women’s bodies.

  1. There are two aspects of “when a human life BEGINS” that your selection (#14) fails to address.

    1. The existence of the actual human being / organism in question.

    2. The significant meaning of the word “begin.”

    Haploid cells have the potential for creating a new organism, but until conception occurs and that potential is realized, that’s all they are. Haploid cells.

    Conception is the earliest point that the New Organism actually “begins.”

    You can’t BEGIN something after it has already began.

    1. I agree that the process of development begins with the fertilized ovum. But the organism cannot survive, given current technology, until a certain point. And that is where I draw my logical, practical, and not theoretical conclusion, which is just my opinion. I could argue in favor of several other stages as well. I just wish the politicians threatening women’s reproductive rights would be expert in biology, or just even understand the basics.

  2. The “organism” is a “human” organism in this case and it HAS began, by your own admission.

    Furthermore, the organism already has biological parents.

    Does it not?

    The question is rhetorical.

    Human beings are “Placental Mammals.” Placental mammals, by definition “carry their YOUNG in the womb as their YOUNG develops towards parturition.

    You can try to justify your support for abortion and the denial of basic human rights some other way. The biological facts are not going to bend to fit that denial.

    1. You misunderstand my intent. I listed many options for defining the start of life to make the point that there are many options! I could just as easily argued for day 5, when the new genome becomes active – as a geneticist, that’s what I’d say. But practically speaking, my personal opinion is that viability outside the woman’s body makes the most sense. I’m trying to provide biological context because much of the public discussion is void of biological facts. Even a “”6-week” heartbeat law is nonsensical, because it is really FOUR weeks from fertilization, not 6! Just trying to educate folks on the biology.

  3. You say, “Life science textbooks from traditional publishers don’t explicitly state when life begins, because that is a question not only of biology, but of philosophy, politics, psychology, religion, technology, and emotions.” Yet, you also seems to vehemently disagree with the philosophical, religious, and political decision made by the Supreme Court of Alabama. You try to make your case that #14 is where life begins more forceful by engaging in the fallacy of appeal to authority, using your own credentials as the “authority.” The problem is that you are not the qualified authority for when life begins, even if you have a great understanding of human development. As you conceded, the question of life’s beginning also rests in other disciplines other than just science. In this case, that definition rests in philosophy, law, and the cultural norms of Alabama. Therefore, in this case, the proper authority was indeed the Supreme Court of Alabama. While the fertilized ovum is seemingly the beginning of a separate organism, it obviously isn’t independent at that time. Alabama simply afforded that organism legal status and protection. Neither is a fertilized eagle’s egg independent immediately. Yet, it is afforded legal protection by our federal government under the Bald and Golden Eagle Protection Act (Before the eagle’s egg can be viable, the organism inside must develop. Nonetheless, it is still alive; separate and distinct from its mother.

    By the way, thank you for the in depth explanation of the earliest stages of human development. I found it very interesting.

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