The chapter examines the nature of anatomical, physiological aspects of human sexuality, as well as the origins of strange dissonances in the sphere. The author interprets them as relics of different stages of anthropogenesis. He emphasizes the close interrelationship of the sexual concerns and structures of both sexes, their mobile unity, and their evolution combining mutual adaptability and conflict. The sexuality of early hominins evolved through comprehensive processes of self-domestication that led to a decline in intragroup violence and the establishment of a norm of voluntary sex. Comparative testicular size in primates, covert ovulation in females, “military” mechanisms of sex cell interaction, and features of the male penis reveal ancient social processes and evolutionary trends. The size of the testes is an indicator of competition between cavaliers during coitus with a female. The main hypotheses of ovulation concealment include: “food for sex”, father retention (“daddy is home”), defense against infanticide. The concept of the “sperm war”, despite heated discussion and criticism, seems to be useful for understanding the ancient transformation of hominin sexuality. The chapter shows the evolutionary significance of menstruation as a mechanism for “evaluating” embryo quality and maternal defense. The excessive size of the human penis has led to several explanatory hypotheses. The author shows how the most plausible versions fit into a plausible chain of evolutionary steps. He proposes theoretical explanations for such habitual peculiarities as the invariable waning of passion during regular intercourse, the long “warming up” of women and the quick “shutting down” of men, and the involuntary female screams during coitus that cause strong male arousal. Judging from many indirect signs, early hominins practiced free group marriage, which provided peacekeeping, child care, and the ability to choose mates. The transition to polygamy and monogamy occurred later, but the ancient structures of sexuality did not change completely, leading to the well-known unrelenting tensions in this area. Finally, the author proposes hypotheses for current cross-cultural and sexological research.