Abstract
Over the last century and a half there has been a secular decline in the age of menarche in Western, industrialized cultures. This trend has been largely ascribed to improved nutrition and health, and we offer an alternative hypothesis that changes in socio-economic conditions have resulted in changes in the pheromonal climate to which prepubertal females are exposed, thereby affecting onset of menarche. Extensive data from non-human mammalian studies indicate that puberty in females is delayed by exposure to adult females, and accelerated by exposure to adult males. The mechanism is pheromonal. The pheromonal climate of the home may have changed since mothers are in the home less (more women now work) and fathers are in the home more (work day of 8 rather than 14 hr). Assuming humans respond similarly to pheromones, this change would contribute to a decline in age of menarche.