It is a debate with important consequences not just for embryo research, but also for wider debates over abortion and infanticide. At the heart of all this lies a central question: Where do we draw the line between a blob of cells and a human being with moral status?
The intractability of this issue reflects the fact that, as a matter of biology, the development of human life is rarely characterized by clear lines. A cell created by a fusion of egg and sperm is (if we ignore the possibility of cloning) a necessary condition of being a human being, but not a sufficient one.
A human being is created in the long journey from being a single, microscopic cell to becoming a self-conscious moral agent. That change does not happen at any one instant, but slowly over time, so that, almost imperceptibly, a qualitatively different being is created.
Read the full article in the International New York Times.