Which of the following is NOT a proposed hypothesis for menstruation?
1) Menstruation provides a defense against pathogens carried by sperm.
2) Menstruation is a byproduct of the way the endometrium thickens.
3) Menstruation helps remove excess iron from the body.
4) Menstruation facilitates the shedding of the uterine lining for potential embryo implantation.