Changes

'''Menstruation''' or '''menses''' occurs at the end of a [[placenta]]l [[mammal]]'s menstrual cycle. There are two types of menstruation:

'''Menstruation''' or '''menses''' occurs at the end of a [[placenta]]l [[mammal]]'s menstrual cycle. There are two types of menstruation:

* Overt menstruation, occuring in [[human]]s and [[great apes]], in which the lining of the [[uterus]] is shed and expelled from the body;

* Overt menstruation, occuring in [[human]]s and [[great apes]], in which some of the lining of the [[uterus]] is shed and expelled from the body;

* Covert menstruation, occuring in all other placental mammals, in which the [[endometrium]] is reabsorbed.

* Covert menstruation, occuring in all other placental mammals, in which the [[endometrium]] is reabsorbed without being expelled.

Over the course of the menstrual cycle, the lining of the uterus builds up in preparation for implantation of a fertilized [[ovum]].  If no conception occurs, the thickened lining is sloughed off and flows out though the cervix and vaginal canal.  The process of thickening then starts again for the next menstrual cycle.<ref>[http://www.4woman.gov/faq/menstru.htm#4 Menstruation and the Menstrual Cycle, from the US Dept. of Health and Human Services]</ref> If conception occurs, hormonal changes occur in the body that prevent menstruation from occurring.

Over the course of the menstrual cycle, the lining of the uterus builds up in preparation for implantation of a fertilized [[ovum]].  If no conception occurs, the thickened lining is sloughed off and flows out though the cervix and vaginal canal.  The process of thickening then starts again for the next menstrual cycle.<ref>[http://www.4woman.gov/faq/menstru.htm#4 Menstruation and the Menstrual Cycle, from the US Dept. of Health and Human Services]</ref> If conception occurs, hormonal changes occur in the body that prevent menstruation from occurring.

* Beverly Strassmann argued that the purpose of menstruation is energy conservation -- that the endometrium is very energy-intensive, so it is more efficient to maintain it for only part of the time.  "Endometrial economy," she argued, preserves the metabolic equivalent of six days worth of food for women.<ref>Strassmann, Beverly I. (1996) "The Evolution of Endometrial Cycles and Menstruation", Quarterly Review of Biology 71, 2(June): 181-221. </ref>

* Beverly Strassmann argued that the purpose of menstruation is energy conservation -- that the endometrium is very energy-intensive, so it is more efficient to maintain it for only part of the time.  "Endometrial economy," she argued, preserves the metabolic equivalent of six days worth of food for women.<ref>Strassmann, Beverly I. (1996) "The Evolution of Endometrial Cycles and Menstruation", Quarterly Review of Biology 71, 2(June): 181-221. </ref>

* Elsimar M. Coutinho argues that menstruation acted as a sign that a woman had failed to conceive in the past, and as such is now "obsolete" and should be "cured" by modern medicine.  <ref>Elsimar M. Coutinho, ''Is Menstruation Obsolete?''</ref>

* Elsimar M. Coutinho argues that menstruation acted as a sign that a woman had failed to conceive in the past, and as such is now "obsolete" and should be "cured" by modern medicine.  <ref>Elsimar M. Coutinho, ''Is Menstruation Obsolete?''</ref>

==Menstruation and the Bible==

==Menstruation and the Bible==