A collaborative team from UCLA, Harvard, UCSF, and the Oregon National Primate Research Center mapped cellular and molecular stages of ovarian reserve formation in rhesus macaques, which share close physiological similarities with humans. Utilizing single-cell sequencing and spatial transcriptomics, the study identified key developmental milestones and cellular players, including hormone-producing cells responsible for the neonatal hormone surge (‘mini-puberty’). This atlas provides a foundational resource to enhance models of human ovarian biology and may inform new treatments for infertility and hormone-related disorders like polycystic ovary syndrome.