The female ducts will then grow and develop into ovaries and a uterus. But this intricate and elegant development of external and internal sexual organs is a journey prone to detours caused by all sorts of influences like maternal hormones, drugs, genetic disposition, environmental hazards, and chance. Sometimes clitorises look more like penises. Sometimes the outer labia on a girl baby fuse into a scrotal-looking sac so her genitals may appear almost indistinguishable from a typical newborn baby boy's. Sometimes a boy's scrotum is empty, his testes undescended, and his penis tiny.
Some vaginas end before they reach the uterus.
These variations occur more frequently than most of us assume. And out of those, about 2,600 children a year are born with genitals that are not instantly recognizable as female or male. But by the 1950s, attitudes toward intervention were changing. Research by John Money, a young sexologist at Johns Hopkins University, suggested that a child's genitals could be altered during the first 18 months of life without undue problems for that child. Along with improved surgical skills and commercially available hormones, this led medicine into a protocol of intervention that still stands.