Polygamy practiced by some 19th century Mormon men had the curious effect of suppressing the overall offspring numbers of Mormon women in plural marriages, say scientists from Indiana University Bloomington and three other institutions in the March 2011 issue of Evolution and Human Behavior.

Simply put, the more sister-wives a Mormon woman had, the fewer children she was likely to produce. "Although it's great in terms of number of children for successful males to have harems, the data show that for every new woman added to a male's household, the number each wife produced goes down by one child or so," said IU Bloomington evolutionary biologist Michael Wade.

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