Talk of embryos -- and the scientific, religious and moral implications of their treatment -- as well as how that treatment is defined and understood, keeps alive the intense debate about when human life actually begins.
At the forefront of the dispute is Scott Gilbert, an internationally recognized Jewish professor of biology at Swarthmore College. His controversial statements, made at a November 2007 Vatican conference, titled "Ontogeny and Human Life," about embryos, and his stand about when they become human beings, created an uproar that continues to resonate on both sides of the issue, in worlds both secular and sacred.
Of the 20 speakers at that conference, Gilbert was the only one who disagreed publicly with the Catholic Church's view that a human being is the result of the process of fertilization.
And, despite his riling statements, Gilbert astonishingly was invited to return to the Vatican under the patronage, he said, of the Pontifical Council for Culture to attend a conference on evolution earlier this year.
Said Gilbert: "One reason for my being invited back is that I have become associated with espousing a particular view of evolution, sometimes called evolutionary developmental biology, and I've written a textbook in this area.
"This view says that evolution represents changes in development and that to understand evolution properly, one needs to have a theory of body construction."
He said that he didn't really know why he -- a Jewish scientist with views so diametrically opposed to the Catholic Church -- had been invited to the first Vatican conference, except perhaps for the textbooks that he'd authored.
"I felt honored to be invited, but I didn't expect to convert anyone to Reconstructionist Judaism. I felt that it was a 'teaching moment' and that I might be able to convince some people that there were other viewpoints that people could have on this issue, and that such people could consider these viewpoints to be as moral as their own."
Among claims of when human life begins, he said, are that "human personhood," as he put it, begins at day 14 after conception, or at gastrulation, with the acquisition of an individual physical identity; and when an embryo is between 24 and 28 weeks old.
"DNA has become synonymous with someone's essence. We're being told all of the time that DNA is our soul; no one knows when ensoulment begins," said Gilbert.
Arthur Kaplan, the renowned University of Pennsylvania-based bioethicist, said that embryos raise the question about the actual versus the potential: "They're not people, not persons; they don't have rights under civil law and under Jewish law. They don't have full moral standing, but they are more than objects. They are potential people."