When Does a Human Life Begin? 17 Timepoints

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(Bonnie Gruenberg photography)

(Bonnie Gruenberg photography)

On September 24, the direct-to-consumer genetic testing company 23 and Me was granted patent no. 8543339, covering the selection of traits in offspring by genotyping eggs and sperm. (“Gamete donor selection based on genetic calculations.”) An analysis of the ethical issues the patent raises is published today in Genetics in Medicine. (Coincidentally, a co-author of the paper was so critical of a recent DNA Science blog post that comments had to be cut off. Small world.)

I’d started thinking about today’s post a few weeks ago, when a prominent science writer posted on a listserv “What was the CEO of AAAS thinking?” and then quoted Alan I. Leshner telling the New York Times: “K-12 students need to know the nature of science, how scientists work and the domains and limits of science. Science can’t tell you about God. Or when life begins.”

“Um…when life begins is a pretty basic idea in biology,” commented the originator of the compelling listserv thread that followed. Actually, no.

I’m the author of an intro college biology textbook called “Life,” my having nabbed that title before Keith Richards did.  Life science textbooks from traditional publishers (I’m with McGraw-Hill) 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 idea comes from that textbooks define life as beginning at conception. 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.” Sneaky.

Being a biologist, a textbook author, and a mother, 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 preference 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.

A human fertilized ovum. (Spike Walker, Wellcome Images)

A human fertilized ovum. (Spike Walker, Wellcome Images)

3. The fertilized ovum. Of the hundreds of sperm surviving the swim upstream to the oocyte, one jettisons its tail and nuzzles inside the much larger cell, which obligingly becomes an ovum, completing its own meisosis. A fertilized ovum = conception.

4. Pronuclei merge, within 12 hours. After fertilization, the packets of DNA from male and female — the pronuclei — approach, merge, and the intermingling chromosomes pair and part, as the first mitotic division looms. A new human genome forms. Following that first division, some genes from the new genome are accessed to make proteins, but maternal transcripts still dominate 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. An 8-celled embryo whose cells are teased apart could lead to an octomom situation.

A day 5 human embryo, at upper left. (David Becher, Wellcome Images)

A day 5 human embryo, at upper left. (David Becher, Wellcome Images)

6. Day 5. The new genome takes over as maternal transcripts are depleted. The inner cell mass (icm) separates from the hollow ball of cells and takes up residence on the interior surface. It will become the embryo proper, distinguishing itself from the remaining part of the ball fated to become the extra-embryonic membranes. The icm is what all the fuss about human embryonic stem (hES) cells is about — the stem cells aren’t the icm cells, but are cultured from them.

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

8. Day 16. The gastrula. Tissue layers form, first the ectoderm and endoderm, then the sandwich filling, the mesoderm. Each layer gives rise to specific body parts.

9. Day 14. The primitive streak forms, classically the first sign of a nervous system and when some nations set the deadline for no longer using human embryos in experiments.

10. Day 18. The heart beats.

11. Day 28. The neural tube closes, within which the notochord, preliminary to the spinal cord, will form, while the bulge at the top will come to house the brain. If the tube doesn’t close completely, a neural tube defect (anencephaly, spina bifida, and a few others) results.

A human embryo on the brink of becoming a fetus.

A human embryo on the brink of  becoming a fetus.

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 in her abdomen that will progress to squirms and kicks from within.

14. Week 22.  A fetus has a chance of becoming a premature baby if delivered.

15. Birth.

puberty16. Puberty. The Darwinian definition of what matters on a population and species level, when reproduction becomes possible.

17. Acceptance into medical school. I don’t know where this came from, a joke about Jewish mothers, but in some circles it might now apply to acceptance into preschool. Or when one’s grown offspring leave home.

My answer? #14. The ability to survive outside the body of another sets a practical limit on defining when a sustainable human life begins.

Having a functional genome, tissue layers, a notochord, a beating heart … none of these matter if the organism cannot survive where humans 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. We can collect and select gametes, now thanks to patent no. 8543339. We collect and select very early embryos in pre-implantation genetic diagnosis, allowing those without a specific disease to continue development. And although the gestational age at which a premature infant can survive has crept younger, it hasn’t by much, not since I starting thinking about these things back when I was a stage #16.

Until an artificial uterus becomes a reality, technology defines, for me, when a human life begins, rather than biology. Alternative views are welcome!

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129 Responses to When Does a Human Life Begin? 17 Timepoints

  1. Chris says:

    The mere fact that we have to as a society to decide when “life” deserves protection under the law shows the deteriation of society as a whole.

    We are the caretakers of earth; therefore, should value all forms of life with respect and dignity.

    To simply end a “life” because the person has equated it to a nuisance could possibly be determined to being selfish.

    To echo another’s sentiments, using technology as basis to determine legality is a frightening slippery slope.

    In the US alone, nearly 40 million fetuses have been “aborted”, almost totaling the number of people who died during WW II.

    I wonder if the author realizes the greatest number of clincis per capita are within areas stricken with poverty. I also fine it ironic that the greatest number of abortions performed are at places called planned parenthood.

    No disease, plague, sickness, cancer, natural disaster, wars, tobacco or any other form of force that ends life can hold a torch to abortion as the greatest vehicle of genocide ever.

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  2. David Michelson says:

    I would say “Thank you all for the enlightening and interesting reading,” but I’ll be really tired tomorrow since I couldn’t stop reading, so I’ll just say “Good night.”

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  3. Thanks to all those who took my question seriously and answered it seriously.

    I accept at face value Dr. Lewis’ answer about wanting to write about the various stages because she’s never seen them all discussed outside of a textbook.

    But that response does not answer my real question: Why is the matter of when life begins even asked in the first place?

    When I wrote the question I thought the short answer was “politics,” but I think the short answer might be a bit too pat, as “politics” is a loaded word. Maybe “ethics” is a little less so. But then again, isn’t ethics about the behaviors and/ or policies that we think are acceptable and not acceptable, and isn’t that what is about too?

    Labels aside, Bob Hunt has two good points. 1) Who has the power to decide who is expendable and who is not?, and 2) what is the criteria for that decision?

    Mveal2006 is also right that at bottom it’s about abortion (which is about ethics, and politics, and about Hunt’s points).

    The comment that has the most resonance with me is the one that David Gaw made because it encompasses all the others. Further, if we answer his question then we answer all the others too.

    The real point of contention is not in defining when life begins, but in defining when moral and/or legal rights ensue.

    And no, the debate is not about a woman’s right to choose whether or not to have an abortion. Just as my right to swing my fist ends at the tip of your nose, a woman’s right to choose abortion ends when that right violates the rights of another person.

    The primary (only?) practical reason we agonize over when life begins is the presupposition that it is at that point when rights ensue. If not for that presupposition the debate would be nothing more than an interesting academic exercise of little or no consequence.

    Is the presupposition correct? (I think not).

    Of the many definitions of when life might begin, most of the debate seems to be centered around the point at which the fetus could survive outside the womb. Sharon makes this point quite eloquently, but I’ll add a couple thoughts anyway.

    It seems that some argue that it takes extreme measures of care for premature babies to survive, and so even survival outside the womb is not the point at which rights ensue. But aren’t even full term babies incapable of surviving without care? So isn’t the question of viability really a question of relative amounts of care? And eo we really want to go down the path of deciding when life begins and therefore when rights ensue based on some predetermined level of care, which means dollars?

    And anyway, isn’t the point at which a fetus can survive much earlier today than it was 10, 20, or 30 years ago? Doesn’t it seem likely that as technology advances that point will continue to be earlier and earlier? Is it all that far-fetched to imagine a time 20, 50, 100 years from now when an egg can be fertilized and grow to full “babyhood” (for lack of a better term) completely outside the womb?

    At some point along that timeline into the future, doesn’t the question of when life begins become a matter of some arbitrary, academic, definition, and therefore for all practical purposes moot? How close are we to that point right now? Have we already passed it and we just don’t know it yet?

    The real question, the most important question, the question that will never become moot, the question for which the matter of when life begins is really just a proxy, is the one that David Gaw suggested; “When do rights ensue?”

    My personal opinion is this: We are all created equal. And while we will probably never EVER really know, outside of some definition that we ourselves rationalize, when life actually begins, we DO know the exact instant at which we are created, and it is in that moment when our rights ensue.

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    • Rebecca Dalmas says:

      This question of rights being based on dependency intrigues me. To be blunt, an embryo or human is often enough referred as a parasite. Yet there are people in state care, right now, who are legally human, legally alive, who are completely dependent on constant care.

      Some would say that yes, but they can be passed on to another person’s care. That is often, but not always the case. I could be closed off from civilization for weeks or even months due to living in a remote location in blizzard conditions, but that does not give me the right to kill my children or abandon them to die.

      The way I see it, we cannot possibly control the gestation of a pregnant woman, especially against her will, but we also do not have to, as a civilized society, take part in killing the unborn within her if she does not want to keep the pregnancy. It is at that point, if she so chooses, that we could say civilization breaks down in reference to her, it won’t support her.
      A woman in this case is not unique. There are endless everyday cases where civilization breaks and is remended, often entirely depending upon one person doing what only they can do, whether it be for a minute or an hour, or weeks, months or years. Conscripted soldiers defend the country. A bystander calls the police to report criminal activity. Parents feed their children. Adult children feed and tend to their elderly parents. Doctors, worn to exhaustion, remain and tend to emergent care cases. Their loved ones wait and support them. A reluctant leader stands and takes a mantle they don’t desire but which is required for the welfare of the whole.
      There are so many times individuals are called upon by society to bear adversity, pain, discomfort, even risking their lives just so civilization can continue. It’s not just about life but human life, and what kind of human life we want to have. Abortion on demand is not civilized.

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  4. Bob Berry says:

    When you argue science, you do not have to even discuss the messy thoughts of moral decisions. Our declaration of independence states that all humans have an unalienable right to life, without declaring when that right is in effect. For me, it is conception, because they are on their way to being born human.

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  5. Kyle says:

    Sadly, Ricki has used imprecise language to confound two different questions, and therefore she perpetuates confusion. The sperm, egg, and all their products possess life, and life has been continuous on planet earth for more than a billion years. The question of when a human life begins is therefore misleading.

    The true question to be debated is: when should our society grant human rights, and civil rights, to the developing individual?

    See how this change of terminology simplifies and clarifies the issue? It also keeps biologists – like me, who make their careers out of the study of life – appropriately distanced from the true debate. Our PhD’s do not give us special leverage on this topic.

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    • My goal was to provide biological information because I am a biologist. I left the philosophy and bioethics for others.

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  6. Thewake52 says:

    Is a healthy 5 minute old baby truly self “sustaining” outside the womb? Or a 5 week old baby? Or a 5 month old baby? or a 5 year old child? Or a 10 year old? Is an 85 year old “sustainable” on their own in many cases? Should culture allow termination of these by others if for someone else the answer turns out to be “no.” And if so, who should that “other” be? The state? The mother, alone. A child of an elderly parent? Who grants that authority? When does the other come into its authority to terminate? When does that authority transfer to the “child”

    The idea of sustainability itself seems arbitrary and leads to a myriad of problems.

    Try another approach.

    At any step along this process, how ever you define or describe it, the fertilized egg it will develop into an independent self sustaining entity for some period of its existence unless some action is taken to prevent it. Now, of course, many events could derail this process “naturally.” But no one considers an uncontrollable or accidental act to be the willful termination of life. And really what we are talking about is when is it acceptable for one human being to make a willful determination to end a life? The Question is uncomfortable so it is easier to shift the terms of the question to a definition of life and then to endless discussions about the countless descriptors we have for the phases of this process: gamete, embryo, baby, child, adult etc. This seems like a convenient diversion.

    The question needs to be focused where it more truly belongs. On the nature of the termination as an act of will. An act of will to terminate only occurs in those cases where allowing the process to unfold will produce a child. No act of will by an other is in play when the termination occurs naturally or accidentally.

    At any stage, again barring the accidental or “natural” failure of some kind, the fertilized egg will become a “sustainable” human being unless someone willfully neglects the child, or actively seeks to terminate it. At what ever stage.

    If allowed to unfold the process will produce, inevitably and inexorably what we will all agree on is a human being. The only thing that will prevent that is a volitional act of essentially violent interference in this process. This is true at any and all stages of the process. At 6 weeks, at 14 weeks, at 22 weeks, and so on.

    The moment doesn’t matter. Every moment along the way is part of a continuum that connects inextricably with the next moment and carries the full potential of the next moment within it. Any act at any time that halts this process prevents a human life from occurring. However you choose to define it.

    Again, without that act of will by one human being, another human being will come into existence. Changing this process anywhere along the continuum -requires a determined act of alteration of, or interference in, or violation of the process already underway. “Life” is already underway, in process, moving forward, and will result in what ever entity you choose to finally call “life” So, logically, it is life at every point and its life is already independent since only an act of interference driven by another’s will can change that.

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    • petrossa says:

      This is getting polemic. The basic premise is, is the infant born capable of full body control functions as it should at the moment of conception. If it isn’t it would die in nature regardless the care of the mother so it isn’t viable. Non-viable life is life that is not meant to be which equals to no life.

      As i said earlier eugenics is a regular daily practice in many civilized parts of the world. In even more civilized parts even postnatal abortion is possible within a timeframe of a couple of hours

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