(Abstracted from Science 2019;365:1466–1469)While it is understood that young females (≥13 years to early 20s) and women of advancing maternal age (AMA, mid-30s or older) have reduced fertility rates, the exact mechanisms behind this feature of the fertility curve remain unclear. Because chromosomal errors and aneuploidy cause a significant amount of pregnancy loss and congenital disorders in women of advanced maternal age, meiotic error rates throughout the entire reproductive life span may shape natural fertility.