Average human males are most likely to be attracted to women with a waist to hip ratio of 0.72. women with this waist to hip ratio are also the most fertile. by being attracted to women with a waist to hip ratio, a male is increasing his chances of having children and thus improve his .

the corpus luteum secretes estrogens and progesterone. the latter hormone causes changes in the uterus that make it more suitable for implantation of the fertilized ovum and the nourishment of the embryo. if the egg is not fertilized, the corpus luteum becomes inactive after 10–14 days, and menstruation occurs.

i hope this : )

the endomembrane system i think