Mormon polygamists of the 19th century had something in common with an unlikely creature: the fruit fly. In the 1940s, geneticist Angus Bateman discovered that the more sexual partners a fruit fly had, the less offspring those partners produced. Scientists examining the polygamous members of the Mormon Church—Brigham Young, for example, had 55 wives and 56 children—observed the "Bateman gradient" in people for the first time, reports the Guardian.
Researchers examined a Utah population database of 186,000 adults who lived between 1830 and 1894, and discovered that "although it is great in terms of numbers of children for successful males to have harems, the data show that, for every new woman added to a male's household, the number of children that each wife produced goes down by one," said a biologist. "It could be owing to competition between women within a plural marriage for shared resources, or it could be owing to other unknown factors," like lack of stamina, said the scientist.