Actually, We Do Know When Human Life Begins

I n a recent New York Times piece asking “When Does Life Begin?,” religion correspondent Elizabeth Dias presents multiple lines of evidence to conclude that the question is simply too complex to be answered. She relays the poignant story of a woman who is pro-choice but who experienced a 16-week miscarriage as the loss of her child, Maya. She enumerates how different states (Arizona, South Carolina), different cultures (China, ancient Egypt), and different religious traditions (Judaism, medieval Christianity) have offered different answers to the question of when life begins. She notes that defenders of the view that life begins at sperm–egg fusion often cite “Christian principles,” suggesting that this conclusion is nothing more than a religious conviction. Dias acknowledges that “more than half of American adults say the statement ‘human life begins at conception, so a fetus is a person with rights’ describes their views at least somewhat well”; yet she goes on to present contrasting views offered by biologists, physicians, philosophers, anthropologists, and clerics.

Let me be clear: Outside of a few quibbles with the biology (the embryo clearly does not arise from a “fraction” of the cells present at the time of implantation; the placenta is manifestly not “a new organ that a woman’s body makes”; and it is absurd to characterize a pregnancy as a woman’s “making a new organism with her body”), I agree with all of the evidence Dias presents and with the obvious fact that opinions on this question are both complex and diverse. What I do not agree with is the conclusion that, simply because people hold diverse opinions on the subject, the question of when life begins cannot be definitively answered.

The question of when human life begins is a matter of biology, not opinion. And the scientific facts are unambiguous: The life of a new human being initiates at the instant of sperm–egg fusion. While some individuals may deny this conclusion, it is supported by hundreds of peer-reviewed scientific papers (discussed here) and is entirely uncontested in the scientific literature. Dias accurately reports that a “scientific consensus” on this question has existed for over 150 years, ever since sperm–egg fusion was first viewed using a microscope. Amander Clark, the president-elect of the International Society for Stem Cell Research (hardly a bastion of pro-life sentiment), clearly endorses this consensus, telling Dias, “From the biologist point of view, I’d need to say life of a mammalian organism begins at fertilization.” In considering the specific question of when human life begins, the mammalian organism in question would be a human organism.  And another term for “human organism” is “human being.”

Given the clarity of the long-standing scientific evidence, why is there such a diversity of opinion on this question? I would argue that a number of confusions and inaccuracies cloud the question, making it appear more complex than it really is.

The irrelevant appeal to historical opinions: It is important to note that prior to the application of medical ultrasound to the field of obstetrics in the late 1950s, human prenatal development was largely inaccessible to direct observation. Consequently, although scientists, philosophers, bioethicists, and theologians have considered the origins of human life for a long time, the conclusions they have drawn were based on very little factual evidence, and appealing to such historical authorities yields a plethora of contradictory opinions, just as Dias notes.

Yet why is it meaningful to appeal to opinions that were formulated centuries before we understood even the most basic biological facts about human life and human embryos? Before microscopes. Before cell theory. Before the discovery of DNA. Opinions formulated in complete ignorance of the relevant biology are free to take any form they choose, and the diversity of those opinions is entirely irrelevant to the actual scientific facts.

Confusing human organisms with human cells: Dias offers the familiar “circle of life” argument to conclude that it is impossible to determine when life begins. Dismissing it as “not a good question,” Cambridge professor Nick Hopwood says: “The egg is alive, the sperm is alive, the cells from which they develop are alive, it is a continuum.” Yet this argument is profoundly misleading. While an embryo arises from the fusion of living sperm and egg cells, an embryo is a human organism, not merely a human cell. And human organisms can be distinguished from human cells by clear scientific criteria (as discussed here and here). The essential characteristic of an organism is the ability of parts to act together in an orderly manner to support the health and survival of the entity as a whole. For multicellular organisms, such as humans, the earliest manifestation of organismal integration is development: the active process of autonomously constructing a mature body. And human embryos immediately enter into a self-directed developmental trajectory that sequentially produces all of the structures required for more mature stages of life. Development is what defines an embryo as an embryo, and this process is entirely distinct from the behavior of mere human cells. The generation of a living organism from living cells is clearly a biologic discontinuity, not a continuum.

Confusions about embryo loss and twinning: The fact that all living human individuals will eventually die does not call into question the humanity of those individuals. Similarly, the fact that a significant number of embryos do not survive to live birth (a number that is greatly exaggerated; see here) is irrelevant to the question of when life begins. Early development is a risky and complex stage of life, much like adolescence. Yet experiencing a high risk of death does not mean you are not (or not yet) alive.

A second challenging aspect of early development is that a single embryo can occasionally split to generate identical twins. For some, this raises doubts about whether the life of a single human being truly begins at sperm–egg fusion. Yet identical twinning is simply a form of asexual reproduction that is common to many animal and plant species, including humans at early stages of life. When an earthworm is cut in half and both halves regenerate to form two identical worms, this does not call the identity of the original worm as a single organism into question. So too for embryos. Substantial evidence indicates that the embryo is a human organism whose life begins at sperm–egg fusion, and twinning does not call this evidence into question (see here for a more detailed discussion of twinning).

Confusing the question of when human life begins with the question of “personhood,” or when a human life is worthy of protection: The diversity of opinion on when life begins largely reflects the diversity of opinion on the independent question Dias raises at the conclusion of her essay: “When does the responsibility for a life begin and end?” We are not struggling with the scientific facts of biology (facts that no one credibly debates). We are struggling with the far more nuanced question of what makes a human being a person; when does a human life become worthy of living? And we have placed this more difficult question under the simpler heading of “When does life begin?”

This is a curious conflation, and one that points to the difficult ethical question we as a society are largely unwilling to engage: What rights are due to human beings at the earliest stages of life?

The belief that equality, freedom, and justice apply universally to all human beings is so deeply rooted in the American mindset, it is difficult to imagine circumstances that could justify depriving any human of these basic rights. Why should any human being be treated unequally under the law? When should the freedom of a human being to live their own life be arbitrarily revoked by another human? Should anyone be refused what is due to them in justice, including the right to life, liberty, and the pursuit of happiness? Because it is difficult to imagine circumstances where a human being should not be granted the basic rights of equality, freedom, and justice, we hide behind an imagined uncertainty regarding whether a human being actually exists prior to birth. But science is certain beyond any reasonable doubt that a human being does in fact exist from the moment of sperm–egg fusion: that the “life of a mammalian organism begins at fertilization.” An inconvenient truth with challenging ethical implications, but a truth nonetheless.