And one more interesting tidbit...
Here's yet another example of how everything is far more complicated than it seems - this Reason article describes some of the fallacies and challenges biologists confront when they attempt to do stem cell research. Here's a very interesting quote, which I hadn't really heard anything about:
John Opitz, a professor of pediatrics, human genetics, and obstetrics and gynecology at the University of Utah, testified before the President's Council on Bioethics that between 60 and 80 percent of all naturally conceived embryos are simply flushed out in women's normal menstrual flows unnoticed.
which leads to this thought:
So millions of viable human embryos each year produced via normal conception fail to implant and never develop further. Does this mean America is suffering a veritable holocaust of innocent human life annihilated? Consider the claim made by right-to-life apologists like Robert George, a Princeton University professor of jurisprudence and a member of the President's Council on Bioethics, that every embryo is "already a human being." Does that mean that if we could detect such unimplanted embryos as they leave the womb, we would have a duty to rescue them and try to implant them anyway?
"If the embryo loss that accompanies natural procreation were the moral equivalent of infant death, then pregnancy would have to be regarded as a public health crisis of epidemic proportions: Alleviating natural embryo loss would be a more urgent moral cause than abortion, in vitro fertilization, and stem-cell research combined," declared Michael Sandel, a Harvard University government professor, also a member of the President's Council on Bioethics.
The article goes on to say that only about half of these embryos are defective in some way - the rest just simply didn't implant for whatever reason. There's also some other very interesting details about the early days of embryonic development, and some suggestions as to how biologists could perhaps make stem cell research palatable for the embryonic right-to-life crowd.