I described it above. You even replied to the post where I did so.
Philosophical ideas about what it means to be a human being/person are all well and good and can play an important part in abortion discussions as well as stem cell research discussions. However, the pro-life side is correct when they say that fetuses are humans. You can reasonable argue that the development of various features informs its rights, but you cannot win an argument saying that a fetus is not a human because that is the biological/taxonomic definition rather than the more philosophical one you want to use. You would be better off arguing that rights increase as maturity does rather than trying to hand wave away the definition of "human" because taxonomy just doesn't count somehow.