Colleen McDannell, a professor of spiritual experiments at the University of Utah, advised "20/20" that for Mormons, intercourse and sexual activity exterior of the bounds of marriage are forbidden. The subsequent marriages of his mother and father yielded 4 50 %-siblings for Gore Vidal - Vance Vidal, Valerie Vidal, Thomas Gore Auchincloss, and Nina Gore Auchincloss - just one stage-brother, Hugh D.