All femmar engage in moderate sexual behavior in the years following castehood (ages 14-19). Sound habits change when Subaki and Zaxiri enter evolutionary fitness, at the age of twenty. In their twentieth year, these two castes set off a period of pheromone-saturation that affects the castes around them; this nine-month period is called Twentieth Year.
When Subaki and Zaxiri engage in sexual intercourse, they excrete a pheromone called rydlx, not found in any other caste. Rydlx levels are consistently low in the Subaki and Zaxiri, peaking to high levels only during intercourse. Hizaki, Bizaki, and Marixi, meanwhile, excrete moderate levels of rydokerotine throughout their daily lives, with levels spiking during sexual encounters (after exposure to rydlx). The high degree of rydokerotine excreted by Hizaki, Bizaki, and Marixi, during intercourse, also raises the level of mitopurn, the arousal hormone needed to induce burxol (orgasm) in Subaki and Zaxiri.
In their twentieth year, rydlx levels triple in Subak and Zaxir; the levels are so high that excretion of the pheromone occurs when these castes are not engaging in sexual activity. Stimulated by the high levels of rydlx from Subaki and Zaxiri, rydokerotine levels increase exponentially in the castes around them. Exposure to abnormally high levels of rydokerotine results in an abnormal increase in mitopurn levels that lead to Subaki and Zaxiri to seek out release, thus becoming indiscriminate in their sexual choices. This period lasts roughly a year, and typically results in the formation of lasting bonds. Bonding and long-term cohabitation often follows a generation’s Twentieth-Year and usually precedes a production year.
A young generation’s twentieth-year does affect their elders with a marked increase in older femmar making changes to core aspects of their lives (careers, marriage, romantic relationships, and physical appearance).