"Joseph Campbell Joke" joke

Our local PBS outlet here has been showing a series of
Joseph Campbell lectures, as they always do when it's
time to wring a little money out of the viewers. On a
recent episode, the late Professor Campbell was talking
about the time when life begins, and he told this little
story:
A Catholic priest, a Protestant minister, and a Jewish rabbi
were discussing when life begins.
"Life begins," said the priest, "at the moment of fertilization.
That is when God instills the spark of life into the fetus."
"We believe," said the minister, "that life begins at birth,
because that is when the baby becomes an individual and is
capable of making its own decisions and must learn about sin."
"You've both got it wrong," said the rabbi. "Life begins
when the children have graduated from college and moved out of
the house..."