Colleen McDannell, a professor of religious scientific tests at the University of Utah, told "20/20" that for Mormons, sexual intercourse and sexual exercise outdoors of the bounds of relationship are forbidden. The subsequent marriages of his mom and father yielded 4 50 percent-siblings for Gore Vidal - Vance Vidal, Valerie Vidal, Thomas Gore Auchincloss, and Nina Gore Auchincloss - one move-brother, Hugh D.