The idea that men are naturally promiscuous and women are naturally monogamous was propped up by a 1948 study by Angus John Bateman that concluded that male flies gain an evolutionary advantage from having multiple partners while female flies do not. The study hadn’t been repeated until recently, at which time scientists realized a fatal flaw in Bateman’s methodology:

“The insects mated freely in the experimental populations, and Bateman examined the children that made it to adulthood. To count the number of adult offspring engendered by each of his original insect subjects, Bateman needed a reliable way to match parents with children.

“Nowadays, modern geneticists would use molecular evidence to determine the genetic parentage of each child, but DNA analysis was not available in the 1940s. Instead, Bateman chose his initial specimens carefully, selecting D. melanogaster flies that each had a unique, visible mutation that could be transferred from parent to child, [UCLA Prof. Patricia Adair] Gowaty said.

“The mutations were extreme. Some of the flies had curly wings, others thick bristles, and still others had eyes reduced in size to narrow slits. […] 

“But by counting only the children with two mutations, Bateman probably got a skewed sample, Gowaty said. In repeating Bateman’s experiment, she and her colleagues found that the flies with two severe mutations are less likely to survive into adulthood. […]

“Bateman concluded that male fruit flies produce many more viable offspring when they have multiple mates but that females produce the same number of adult children whether they have one mate or many. But Gowaty and her colleagues, by performing the same experiment, found that the data were decidedly inconclusive.

“[Gowaty:] ‘Bateman’s results were believed so wholeheartedly that the paper characterized what is and isn’t worth investigating in the biology of female behavior.’ […]”

“‘Our worldviews constrain our imaginations,” Gowaty said. “For some people, Bateman’s result was so comforting that it wasn’t worth challenging. I think people just accepted it.‘”

-“Biologists reveal potential ‘fatal flaw’ in iconic sexual selection study.” ScienceDaily, 26 Jun. 2012. Web.