Menstrual cycle of progesterone, the uterine lining changes to prepare for potential implantation of an embryo to establish a pregnancy. If implantation does not occur within approximately two weeks, the corpus luteum will involute, causing a sharp drop in levels of both progesterone and estrogen. The hormone drop causes the uterus to shed its lining in a process termed menstruation. Menstruation also occurs in closely related primates (apes and monkeys). The average age of menarche is 12–15. They may occasionally start as early as eight, and this onset may still be normal. This first period often occurs later in the developing world
Menstrual cycle it has been found that women in the follicular phase demonstrated better performance in tasks that contain empathetic traits. Fear response in women during two different points in the menstrual cycle has been examined. When estrogen is highest in the preovulatory stage, women are significantly better at identifying expressions of fear than women who were menstruating, which is when estrogen levels are lowest. The women were equally able to identify happy faces, demonstrating that the fear response was a more powerful response. To summarize, menstrual cycle phase and the estrogen levels correlates with women’s fear processing. However, the examination of