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A number of hypotheses have been put forth regarding the purpose or benefit of menstruation:

A number of hypotheses have been put forth regarding the purpose or benefit of menstruation:

* The ancient physician [[Hippocrates]] held that menstruation was the body's means of purging itself of bad [[humor]]s, based on his belief that an excess of blood in the body led to health problems;

* The ancient physician [[Hippocrates]] held that menstruation was the body's means of purging itself of bad [[humor]]s, based on his belief that an excess of blood in the body led to health problems;

* Margie Profet argues that menstruation was the body's means of purging the uterus and reproductive system of bacterial infection, based on the fact that menstrual blood contains an unusually large amount of macrophages, or immune cells <ref>http://www.ncbi.nlm.nih.gov/pubmed/8210311</ref>;

* Margie Profet argues that menstruation was the body's means of purging the uterus and reproductive system of bacterial infection, based on the fact that menstrual blood contains an unusually large amount of macrophages, or immune cells;<ref>http://www.ncbi.nlm.nih.gov/pubmed/8210311</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>

* 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>

== Overt and covert menstruation ==

== Overt and covert menstruation ==