Due to their advanced senses of smell, barasts are very sensitive to pheromones. Accordingly, women and men live in separate communities for 25 out of every 29 days. The four days when they do come together — known as "two becoming one" — are the cause of a monthly celebration and holiday. All barast women have synchronized menstrual cycles, and the meeting-times are set so that conception is unlikely — except every 10 years, when another generation is purposely conceived. Generations thus grow in synchronized, ten-year cycles; no barast needs to give his age, as simply stating his generation (if this is not simply inferred from his appearance) will give the needed information.