Abstract

The evolutionary history of the male and female reproductive tracts is reflected in the human embryology and adult anatomy. The sexually indifferent gonad consists of primary and secondary sex cords. The primary cords proliferate in the medulla and the secondary cords regress in the male gonad, forming a testis, whereas the secondary sex cords proliferate from the cortex of the female gonad, forming an ovary. The persistence of both primary and secondary sex cords in primitive vertebrates allows for the rare phenomenon of functional hermaphroditism, where the gonad can function as a testis or ovary. The internal genitalia are formed from two sets of ducts; the paramesonephric ducts form the female internal structures and the mesonephric ducts form the male internal structures. The paramesonephric ducts are primitive in many aquatic vertebrates that exhibit external fertilization and development of the embryo, whereas the ducts form a muscular and vascular uterus in mammals, allowing the embryo to develop and grow internally. The male and female external genitalia are formed by the same embryonic precursors, which are feminized in the absence of male hormones, or which undergo virilization in the presence of dihydrotestosterone. The embryology of the male and female reproductive system is reflected in its evolutionary history; therefore a basic knowledge of comparative anatomy facilitates a better understanding of human development.

Keywords: Comparative anatomy; Paramesonephric; Mesonephric; Cloaca; Reproductive embryology