Colleen McDannell, a professor of religious scientific tests at the University of Utah, explained to "20/20" that for Mormons, sex and sexual action exterior of the bounds of relationship are forbidden. The subsequent marriages of his mom and father yielded 4 half-siblings for Gore Vidal - Vance Vidal, Valerie Vidal, Thomas Gore Auchincloss, and Nina Gore Auchincloss - 1 stage-brother, Hugh D.