The net result is that slightly fewer than a third of all conceptions lead to a fetus that has a chance of developing. In other words, if you were to choose a zygote at random and follow it through the first week of development, the chances are less than one in three that it would still be there at full term, even though there has been no human intervention. Nature, it seems, performs abortions at a much higher rate than any human society. It is simply not true that most zygotes, if undisturbed, will produce a human being.
American biophysicist (1927-2016)
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Even with this abbreviated sketch of the process of fertilization, one thing is obvious. When biologists object to statements about life beginning at conception, they are not splitting hairs or being pedantic. There is no time in the sequence we’ve just described where new life is created. In fact, from the point of view of the biologist, at conception, two previously existing living things come together to form another living thing.
The end point of this reasoning is that any policy based on assigning a unique status to conception in the emergence of humanness must be seen as coming from subjective evaluations—evaluations that may not be shared by others. Subjectivity does not, of course, does not make these arguments wrong; it simply means that they cannot be given the kind of public universality we assign to arguments grounded in scientific understanding.
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We recognize that to many people such a statement of cold biological fact misses something essential about the developing fetus. We recognize that there is a strong inclination to assign personhood or a soul to the single cell that results from fertilization on the grounds that it represents “potential life.” Our position is that this inclination, as strongly as it may be favored on religious or social grounds, has no basis in science because, as we point out in Chapter 1, personhood and soul are simply not scientific concepts.
Decisions cannot be made on purely scientific grounds. We can, however, use scientific information to guide our moral and political judgments. No matter which side of the debate we take in any public dispute, we should, at a minimum, get the facts straight and understand the scientific dimensions of the problem.
In the end, the abortion controversy comes down to one question: Will this particular pregnancy be terminated or not? There are only two possible choices, neither good. One is to abort the fetus. The other is to demand that the pregnancy be brought to term and, in effect, to compel the birth of an unwanted child. The second choice is repugnant to me. Not only does it entail real and immediate risks for the mother, but it may create a lifetime of misery for the child – misery that will, in all likelihood, persist for generations. Frankly, I can imagine fewer human acts more deeply evil than bringing an unwanted child into the world.