In many respects the current debate about embryo experimentation resembles the older debate about abortion. Although one central argument for abortion–the claim that a woman has the right to control her own body–is not directly applicable in the newer context, the argument against embryo experimentation remains essentially the same as the argument against abortion. This argument has two forms, one relying on the claim that from the moment of fertilization the embryo is entitled to protection because it is a human being, and the other asserting instead that the embryo is entitled to protection because from the moment of fertilization it is a potential human being.

The first form of this argument is considered in Chapter 5; our focus is on the argument from potential. Those who use this argument against embryo experimentation frequently describe the potential of the early in vitro embryo in terms which are identical with the terms used to describe the potential of the early embryo inside the female body in the context of the abortion debate. For example, Teresa Iglesias, writing on in vitro fertilization, says: ‘We know that a new human individual organism with the internal potential to develop into an adult, given nurture, comes into existence as a result of the process of fertilization at conception.’

But can the familiar claims about the potential of the embryo in the uterus be applied to the embryo in culture in the laboratory? Or does the new technology lead to an embryo with a different potential from that of embryos made in the old way?