The embryo, George and Tollefsen argue, is a whole being, possessing the integrated capability to go through all the phases of human development.
[This argument favours rather the opposite conclusion: since embryos have just the capability, they haven’t gotten through all the phases of human development, i.e., they are not completely human. A similar problem is recognised by the authors of the book, as we see below:]
An embryo has what it takes to be a free, rational, deliberating, and choosing being; it is naturally fitted to develop into a being who can be an “uncaused cause,” a genuinely free agent. Some will object, of course, that the embryo is only potentially human. The more precise version of this objection is that the embryo is human — not a fish or a member of some other species — but not yet a person. A person, in this view, is conscious enough to be a free chooser right now. Rights don’t belong to members of our species but to persons, beings free enough from natural determination to be able to exercise their rights. How could someone have rights if he doesn’t even know that he has them?