In ‘Naming and Necessity,’ Saul Kripke defends a number of essentialist claims. One of them is that having a certain origin is a necessary property of a material thing. Used in connection with a human being or, presumably, a living thing of another kind whose members sexually reproduce, ‘necessity of origin’ means that the organism must have been born of those individuals who are its parents, i.e., whose body tissues are sources of the sperm and egg from which it issued, in the actual world. To say that the origin of an inanimate material thing is necessary is to say that having its origin in the hunk of matter from which it came is essential to it.