While there exist numerous reviews on the problem of sex, the historical side of the research in this field is often only loosely covered. Here, I provide a more detailed historical overview by analyzing the contributions of four of the most influential biologists: Charles Darwin, August Weismann, Ronald Fisher and John Maynard Smith. More specifically, I discuss why these four biologists became interested in the significance of sex in the first place, describe their respective theories on sexual reproduction and in which context those theories were developed. This approach provides a general overview over the conceptually important changes in the history of the research of sex. Most importantly, it shows that not only the potential answers on the existence of sex have evolved, but also the question itself.