Women's affiliation across the menstrual cycle: Cycle phase variation and associations with progesterone and estradiol.

Throughout history, women have faced numerous threats during pregnancy, some of which can be mitigated by a strong social network. Consequently, women may demonstrate behavioral changes that bolster their social support network during pregnancy and in the luteal phase of the menstrual cycle. We examined whether women's explicit desire to affiliate varied across menstrual cycle phases and was associated with within-woman fluctuations in progesterone and estradiol.