The slogan "human life begins at conception" embodies pro-life advocates' position that a new human being comes into existence at the moment an ovum is fertilized. The unstated assumption behind the slogan is that "personhood" begins at the same time as "human life", and therefore the fertilized egg is a person with a right to life from the very moment of conception.

Pro-choice advocates argue that the slogan human life begins at conception is potentially confusing or misleading. They agree that it may be technically true in one sense, but charge that it deliberately uses ambiguous language to gloss over the crucial issue of the time personhood begins at - an issue on which there is a wide scale of opinion. They attribute any force the slogan has to the exploitation of this confusion.

Pro-choice advocates, while acknowledging that the living biological tissue of an early fetus is human - just as body parts such as a white blood cell, sperm cell, or a finger are "human" - do not consider the early fetus to be a person. Most do concede, however, that as the fetus develops and approaches birth, its claim to be considered a person increases.

A moderate pro-life position is that personhood begins at viability; an extreme position is that it begins at birth. Other positions exist.

Because the fetus is in a constant state of development, many on the pro-choice side would admit that it is difficult to find a sharp cut-off point at which it obviously becomes a person. This is one reason why the "at conception" slogan has the appeal (to some) that it does, as it seems to offer a clear, unambiguous solution.

The human conceptus is not necessarily an individual. But individuality is essential to personhood. Therefore, the conceptus cannot be reasonably regarded as a person." Proponents of this argument cite as evidence the fact of so-called "identical" twins and other multiple births resulting from the causality of a single ovum and sperm. They rightly insist that the living zygote which divides in half cannot be viewed as one, identical human being dividing into two.

Jerome Lejeune of Paris, for instance, has indicated that individuality may be fully existent at the point of fertilization, but that so far we do not have the technical capacity to discern how many individuals are present at that point. Also, at this early stage of human development there may occur at times a process of generation similar to that common in other species. In that case, we could say that one of the twins would be the parent of the other. The original zygote could be regarded as the parent of the second, even though we may never know which one was parthenogenically the parent.

See also:

• abortion, legal and moral issues
• religion and abortion
• "A woman's right to choose"

External links

• Survey of several alternative definitions (http://www.pregnantpause.org/develop/when.htm)
• Some less-common scientific viewpoints - An interesting list but the author does seem to conflate the terms 'life' and personhood. (http://zygote.swarthmore.edu/intro5.html)
• Abortion viewpoint (http://www.andkon.com/stuf/abortion/) - A short essay arguing that "a fetus is a human and not a parasite".
• - Personhood and the Conception Event by Robert E. Joyce. (http://www.homestead.com/lifemeaning/Personhood.html)