|From "Why It Matters that Life Begins at Birth Not Conception" by Ari Armstrong and Diana Hsieh, Ph.D.:|
From the moment of fertilization to its implantation in the womb a few days later, the zygote consists of a few largely undifferentiated cells. It is invisible to the naked eye. It has no human organs, and no human form. It has no brain, and so no capacity for awareness or emotions. It is far more similar to a few skin cells than [to] an infant. Moreover, the zygote cannot develop into a baby on its own: its survival beyond a few days requires successful implantation in the lining of the woman's uterus. If it fails to do that, it will be flushed from her body without anyone ever knowing of its existence.
If the embryo matures normally after implanting into the lining of the uterus, it gradually develops primitive organs. Yet its form is not distinctively human in the early stages: it looks very similar to the embryo of other species. As it develops its distinctive human form, the fetus remains wholly dependent on the woman for its survival. . . . So before viability, the fetus is not capable of an existence independent of the pregnant woman.
After 26 weeks, when a fetus would be viable outside the womb, its organs continue to mature in ways critical to its survival and well-being after birth. It is aware, but that awareness is limited to the world inside the womb. Most importantly, however, so long as the fetus remains within the woman, it is wholly dependent on her for its basic life-functions. It goes where she goes, eats what she eats, and breathes what she breathes. It lives as she lives, as an extension of her body. It does not interact with the outside world. It is wholly contained within and dependent on her for its survival. So if the woman dies, the fetus will die too unless delivered quickly. The same is true if the fetus's life-line to her body is disrupted, such as when the umbilical cord forms a tight knot. A fetus cannot act independently to sustain its life, not even on the basic biological level possible to a day-old infant. It is thoroughly and solely dependent on the woman in which it lives.
That situation changes radically at birth. A baby lives his own life, outside his mother. Although still very needy, he maintains his own biological functions. He breathes his own air, digests his own food, and moves on his own. He interacts with other people as a whole and distinct creature in his own right, not merely as a part of a pregnant woman. He can leave his mother, either temporarily or permanently, to be cared for by someone else.
These important differences between the mode of life of the zygote, embryo, and fetus on the one hand, and the born infant on the other, show that the former cannot be persons. Rights, in other words, cannot be applied until birth. Why not?
First, the utter biological dependence of the zygote, embryo, and fetus on the pregnant woman shows that, until birth, it is not yet living its own life, but rather partaking in the life of the woman. It exists as part of the pregnant woman, not as an individual in its own right. Yet rights pertain only to individuals, not parts thereof. Such is the case, even when the fetus would be viable outside the womb. Even then, it is only a potential individual, not an actual one. The fetus only becomes an actual individual when birth separates it from the woman's body. Until then, it cannot be a person with a right to life. The pregnant woman, in contrast, is always an individual with full rights.
Second, the zygote, embryo, or fetus does not exist in a social context until birth. Due to its enclosure within the body of the pregnant woman, the new life cannot interact with other people: it experiences only muffled sounds and indirect pressure through the woman. It cannot be touched or handled, nor can it even engage in the primitive communication possible to infants. Even the pregnant woman cannot directly interact with her fetus, as she will do with her newborn infant. Until birth, she can only act as a biological host to the life inside her, not as a mother. A woman, in contrast, lives in society whether pregnant or not--and her rights are therefore absolute and inalienable.
Given these facts, to ascribe any rights to the zygote, embryo, or fetus before birth is a profound error. It is not a person--or rather, it is only a potential person, not an actual person. To suppose that mere potentiality is sufficient is to commit the fallacy of the continuum. The fact that a zygote may develop into a born infant does not prove the zygote to be the same thing as a born infant--any more than an acorn is an oak tree and a caterpillar is a butterfly. As philosopher Leonard Peikoff observes, treating a zygote--a potential person--as though it were an actual person makes no more sense than treating an adult human--a potential corpse--as though he were an actual corpse.