Moment of Conception

Since the point at which a fertilized human egg becomes "human"  has become a talking point for anti-abortion types following Obama's answer ("above my pay grade ") at the faith forum Saturday night, Andrew Sullivan felt it necessary to remind us all just what the biological facts are. Quoting Steven Pinker's book Blank Slate:

"Just as a microscope reveals that a straight edge is really ragged, research on human reproduction shows that the 'moment of conception' is not a moment at all. Sometimes several sperm penetrate the outer membrane of the egg, and it takes time for the egg to eject the extra chromosomes ... Even when a single sperm enters, its genes remain separate from those of the egg for a day or more, and it takes yet another day or so for the newly merged genome to control the cell. So the 'moment' of conception is in fact a span of twenty-four to forty-eight hours."