In a popular form, the author analyzes the causes of the appearance of the sexes, their functions in the process of reproduction, the motives for the convergence of the sexes from the historical scene. The work examines the factors contributing to the birth of a child of one sex or another, outlines the prospects for the development of family-marriage relations, for the first time offers reasoned solutions to the so-called sexual phenomena (excessive birth of boys in wartime, a decrease in the proportion of girls in the offspring of unhealthy men, an increase in the likelihood of having daughters in women who have suffered stress before and during pregnancy, etc.).