Gambler's fallacy
As early as 1796, the idea of the gambler's fallacy was used to "predict" the sex of children. In his work A Philosophical Essay on Probabilities, published in 1796, Pierre-Simon Laplace wrote of the ways in which men calculated their probability of having sons:"I have seen men [who wanted to have] a son, who could learn only with anxiety of the births of boys in the month when they expected to become fathers. Imagining that the ratio of these births to those of girls ought to be the same at the end of each month, they judged that the boys already born would render more probable the births next of girls." In short, the expectant fathers feared that if more sons were born in the surrounding community, then they themselves would be more likely to have a daughter.