In science it often happens that scientists say, 'You know that's a
really good argument; my position is mistaken,' and then they would
actually change their minds and you never hear that old view from them
again. They really do it. It doesn't happen as often as it should,
because scientists are human and change is sometimes painful. But it
happens every day. I cannot recall the last time someting like that
happened in politics or religion.
-- Carl Sagan, 1987 CSICOP Keynote Address