During the 19th century, scientists and physicians came to understand that the life of a human being (an individual member of the species Homo sapiens) begins at conception. The old idea that "quickening" was relevant to the nature of unborn children had been shown to be biologically mistaken. "The true scientific position,” explained an essay published in 1866 in the United States Medical and Surgical Journal, "is this: from the moment of conception, when the spermatozoa coalesces with the cell-wall of the ovule, the ovum is a distinct human being." For Americans of this era, the humanity of unborn children settled the question of the morality of killing them. "Because the medical and legal establishment presupposed the moral axiom against killing innocent human beings," writes Justin Buckley Dyer in his historical treatment of the subject, "the physicians involved with the anti-abortion movement in the nineteenth century thought a demonstration that life begins at conception was sufficient to establish the wrongness of abortion at any point during pregnancy." Unborn children are, as a matter of empirical fact, human beings. Intentionally killing innocent human beings is wrong. So abortion is wrong. Case closed. Unborn children deserve protection just like all other members of the human family. Consequently, in the mid- to late-19th century, states replaced the common law or earlier anti-abortion statutes with statutes banning all elective abortions, both before and after quickening. But the commonsense view that killing innocent human beings is wrong isn't as common now as it was back then. A 1970 editorial in the California Medical Association's journal called for abandoning the "traditional western ethic" that upholds "the intrinsic worth and equal value of every human life regardless of its stage or condition." Instead, "it will become necessary and acceptable to place relative rather than absolute values on such things as human lives," the editorial explained. Of course, "since the old ethic has not yet been fully displaced," the authors noted, "it has been necessary to separate the idea of abortion from the idea of killing, which continues to be socially abhorrent. The result has been a curious avoidance of the scientific fact, which everyone really knows, that human life begins at conception and is continuous whether intra- or extra-uterine until death." In the subsequent years, that scientific fact became much, much harder to avoid, especially with the development of ultrasound technology. Acceptance of abortion, then, required that "the idea of killing" become less socially abhorrent. And, to a certain degree, it has. In 1973, the U.S. Supreme Court erased all of the 19th century laws protecting unborn children, effectively legalizing abortion for any reason nationwide. Most Americans didn't (and still don't) agree with the radical extent and consequences of that decision. Nevertheless, many in our society have indeed rejected the view—taken for granted by doctors in the 19th century—that killing innocent human beings is simply wrong. They don't support killing in general, of course. But they think it's permissible to kill human beings in utero who, according to this view, lack the value or rights or "personhood" that older members of our species enjoy. "Merely being human is not in itself a reason for ascribing someone a right to life," write two philosophers (who defend both abortion and infanticide) in the Journal of Medical Ethics. "So what if abortion ends life?" asks one writer for Salon. "All life is not equal."
This current debate is similar, in one important respect, to the disagreements over other issues among the same 19th century Americans who prohibited abortion. Those Americans rejected discrimination against human beings on the basis of age, size, dependency, or location (in the womb or out). But many of them, horrifically, still defended discrimination on the basis of race, ethnicity, and sex. Today the reverse is true. Our society discriminates against the young and small while cherishing diversity of race, ethnicity, and gender. But the core principle that is at stake—the principle of human equality—is the same with regard to all of these issues. It's the same principle Americans grappled with 150 years ago. It's also the principle laid down in the beginning of our nation's founding document. We must work harder to live up to it.