John W. Gunnison reported in his book that Latter-day Saints practiced polygamy to account for population differences between men and women.
John W. Gunnison, The Mormons, or Latter-Day Saints, in the Valley of the Great Salt Lake (Philadelphia: Lippincott, Grambo, 1860), 71
It is further maintained that there is great disparity of numbers between the sexes, and that the predominance of the female is more than can be accounted for from war, the dangers of the sea and other perils, and therefore nature indicates the propriety of plurality, as "marriage is honorable to all;" but the decision of this question can safely be instrusted to the relative numbers of the sexes, as exhibited in our census returns.