DOES JESUS have a secret line of descendants who are living today? It's an oddly appealing idea. We tend to think of ancestry in terms of bloodlines, in which some individuals are descended from famous ancestors and others are not. And the idea echoes deeper religious themes of individuals and groups favored by God. But this is one idea in "The Da Vinci Code," which opens today in theaters worldwide, that just won't wash. Jesus couldn't have just a few descendants living today. If anyone alive today is descended from Jesus, then so are most of the people on the...