Before deciding how we ought to treat the unborn—a moral question—we must first be clear about what the unborn is. This is a scientific question, and it is answered with clarity by the science of human embryology.
When sperm fertilizes egg
The facts of reproduction are straightforward. Upon completion of the fertilization process, sperm and egg have ceased to exist (this is why "fertilized egg" is an inaccurate term); what exists is a single cell with 46 chromosomes (23 from each parent) that is called a zygote. The coming into existence of the zygote is the point of conception—the beginning of the life of a new human organism. The terms zygote, embryo and fetus all refer to developmental stages in the life of a human being.
Four features of the unborn
Four features of the unborn (i.e., the human zygote, embryo or fetus) are relevant to his or her status as a human being. First, the unborn is living. She meets all the biological criteria for life: metabolism, cellular reproduction and reaction to stimuli. Moreover, she is clearly growing, and dead things (of course) don't grow.
Second, the unborn is human. She possesses a human genetic signature that proves this beyond any doubt. She is also the offspring of human parents, and we know that humans can only beget humans (they cannot beget dogs or cats, for instance). The unborn may not seem to "look" human (at least in her earlier stages), but in fact she looks exactly like a human at that level of human development. Living things do not become something different as they grow and mature; rather, they develop the way that they do precisely because of the kind of being they already are.
Third, the unborn is genetically and functionally distinct from (though dependent on and resting inside of) the pregnant woman. Her growth and maturation is internally directed, and her DNA is unique and different from that of any other cell in the woman’s body. She develops her own arms, legs, brain, central nervous system, etc. To say that a fetus is a part of the pregnant woman’s body is to say that the woman has four arms and four legs, and that about half of pregnant women have penises.
A whole organism
Fourth, the unborn is a whole or complete (though immature) organism. That is, she is not a mere part of another living thing, but is her own organism—an entity whose parts work together in a self-integrated fashion to bring the whole to maturity. Her genetic information is fully present at conception, determining to a large extent her physical characteristics (including sex, eye color, skin color, bone structure, etc.); she needs only a suitable environment and nutrition to develop herself through the different stages of human life.
Affirmed by textbooks, scientists
This fact is confirmed by embryology textbooks and leading scientists, who could be cited here ad nauseam. In The Developing Human: Clinically Oriented Embryology, perhaps the most widely used embryology text, Keith L. Moore and T.V.N. Persaud explain: "Human development begins at fertilization when a male gamete or sperm (spermatozoon) unites with a female gamete or oocyte (ovum) to form a single cell -- a zygote. This highly specialized, totipotent cell marked the beginning of each of us as a unique individual."
Langman's Embryology notes, "The development of a human begins with fertilization, a process by which the spermatozoon from the male and the oocyte from the female unite to give rise to a new organism, the zygote."
Adds Dr. Micheline Matthews-Roth of Harvard Medical School, "It is scientifically correct to say that an individual human life begins at conception, when egg and sperm join to form the zygote, and this developing human always is a member of our species in all stages of its life."
In 1981 a U.S. Senate judiciary subcommittee heard expert testimony on the question of when life begins. The official subcommittee report reached this conclusion:
"Physicians, biologists, and other scientists agree that conception marks the beginning of the life of a human being—a being that is alive and is a member of the human species. There is overwhelming agreement on this point in countless medical, biological, and scientific writings."
The report also noted that "no witness [who testified before the subcommittee] raised any evidence to refute the biological fact that from the moment of conception there exists a distinct individual being who is alive and is of the human species. No witness challenged the scientific consensus that unborn children are 'human beings,' insofar as the term is used to mean living beings of the human species."
Evidence is decisive
The evidence, then, shows that the unborn is a living organism of the human species from his or her beginning at conception. Thus, to kill the unborn by abortion or for embryo-destructive research is to kill a human being. This is not a moral claim about whether such killing is right or wrong, but a factual one, based on the scientific evidence of embryology.
Objections to this conclusion stem from scientific ignorance, confusion or misunderstanding. I consider common objections below.
Objection #1: 'No one knows'
The claim that "no one knows when life begins" is so often repeated that it bears addressing. While there is indeed debate about when a human being becomes (if she isn't by nature) valuable and deserving of full moral respect (i.e., a "person"), the strictly biological matter is clear, as I explain above. The life of a human being, a living member of our species, begins at conception.
(Contrary to what many pro-choice advocates apparently believe, agnosticism regarding the unborn is actually a decisive reason to refrain from killing her. A hunter does not shoot into the brush unless he is sure that his target is not a person.)
|Ultrasound image of unborn child|
Some say that if the unborn is a human being, then we must (absurdly) conclude that the sperm and egg are also human beings, for they also have the potential to become a child, a teenager and eventually an adult.
This is bad biology. The sperm and egg are simply parts of larger organisms. When they unite they cease to be and something new comes into existence: the zygote, a whole organism with the active capacity to develop into a mature member of its species, given only a suitable environment and nutrition. Each of us was once a zygote, but none of us was ever a sperm or egg.
Objection #3: Somatic cells
Some people compare the zygote and embryo to regular somatic (body) cells, which are also human, living and possessing of a full genetic code. Since these cells are not actual human beings—brushing skin cells off my arm is not the killing of hundreds of tiny humans—the zygote or embryo is not an actual human being either, the critic reasons.
But there is a crucial difference. The unborn is its own organism, not a mere part of another. The unborn from conception is a distinct and complete individual whose parts work together in a coordinated fashion to develop the whole to maturity. That is not true of skin or other somatic cells, which function as mere parts of a larger organism.
Objection #4: Twinning
Defenders of embryo-destructive research sometimes say that because very early embryos can split into two distinct embryos—an event called twinning—the early embryo must not itself be a unitary individual. But the conclusion does not follow.
When a flatworm is cut in half, or when an organism is cloned via somatic cell nuclear transfer, a single organism gives rise to two distinct organisms. In both cases the original entity is a unitary, self-integrating, whole individual. The scientific evidence shows that the embryo likewise functions as its own organism, from the zygote stage forward, regardless of whether twinning occurs.
Objection #5: Brain death
The irreversible cessation of brain activity is used as a criterion for the death of a human being, even though some of the body’s organs can live after brain death. For this reason, some advocates of embryo-destructive research claim that the life of a human being does not begin until the unborn develops a brain.
But brain death is accepted as a criterion only because it signals the end of the body's ability to function as an integrated organism, for which the brain, in older humans, is essential. After brain death there is no longer a unitary organism. By contrast, the embryo from conception is a unitary organism, actively developing herself to the next stage of human life. The brain, at this earliest stage, is not yet necessary for her to function as such.
All, or only some?
Because the scientific facts are clear, the permissibility of taking unborn human life hinges on a moral question. Do all human beings merit full moral respect and protection, as you and I uncontroversially do—or only some?