When does human life begin?
Though not my intention to bring uscatholic.org down in a blaze of fury, I thought I'd pass along a Religion News story on a Missouri law  that defines when human life begins: ''The life of each human being begins at conception," according to Senate Bill 793, which adds new regulations to the state's 24-hour informed consent law for abortions. "Abortion will terminate the life of a separate, unique, living human being."
Not withstanding the legal force of such statement, which I can't figure out since it doesn't pre- or proscribe anything, the underlying assumption of the RNS story is that the claim is theological, specifically a Roman Catholic belief. RNS goes on to cite other religious traditions' approaches to the question, with some interesting results.
Jewish: "The question for Jewish law is not when does life begin, but when is the embryo entitled to the justice and compassion of society?" (Rabbi Yehiel Poupko of the Jewish Federation of Metropolitan Chicago)
Muslim: "[Most Sunni Muslims believe] life begins at the turn of the first trimester." (Abdulaziz Sachedina, professor of Islamic Studies at the University of Virginia)
Hindu: "Life cannot begin at conception when our lives have not ended in the first place." (Cromwell Crawford, retired professor, University of Hawaii)
I think the predominant Catholic tradition is that "human life begins at conception" is a principle of natural law rather than revelation, which means that anyone should be able to come to that conclusion regardless of faith. It's clear that convincing even other religious people of that is a challenge in a religiously pluralistic world, much less a secular one.