[David O. McKay]
You state in your letter that you 'have been going with girl for the past two years whose mother and your grandmother are half sisters, both having the same father,' and you ask my opinion as to the advisability of your marrying.
Of course you understand that the laws of Utah prohibit first cousins from marrying. The Church however, has made no ruling against such unions. One of my dearest friends, a leading man in the Stat of Utah, married his first cousin and has reared one of the choicest families in the State' they excel in intellectuality and in moral character.
[David O. McKay, Letter to Darrel L. Crane, as quoted in Minutes of the Apostles of The Church of Jesus Christ of Latter-day Saints, 1910-1951, Privately Published, Salt Lake City, Utah 2010]