Volume of Menstrual Blood Loss

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Human Uniqueness Compared to "Great Apes": 
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Menstrual blood loss occurs in many primates, including humans and apes. The volume of blood lost varies substantially across species. Normal human females lose approximately 80 ml of fluid per menstrual cycle, with blood comprising about half of that volume. This volume is significantly greater in humans than in gorillas and orangutans. Anecdotal evidence suggests the human volume is also greater that of chimpanzees, although these claims have not been specifically quantified. The volume of blood lost through human menstruation is thought to underlie the high rate of iron deficiency found in women. It has also been suggested to cause significant predator risk. A number of speculative theories have been put forward to explain the reasons for the high volume of human menstrual blood loss, including that it provides protection from pathogens in semen, that it is an incidental result of characteristics of endometrial vasculature or the hemochorial placenta, that it is caused by the relatively large size of the human uterus, that it reduces the energy cost of endometrial regression, or that it defends against uterine neoplasm. Many human societies have strong menstrual taboos, regulating the activities of menstruating women.


Timing of appearance of the difference in the Hominin Lineage as a defined date or a lineage separation event. The point in time associated with lineage separation events may change in the future as the scientific community agrees upon better time estimates. Lineage separation events are defined in 2017 as:

  • the Last Common Ancestor (LCA) of humans and old world monkeys was 25,000 - 30,000 thousand (25 - 30 million) years ago
  • the Last Common Ancestor (LCA) of humans and chimpanzees was 6,000 - 8,000 thousand (6 - 8 million) years ago
  • the emergence of the genus Homo was 2,000 thousand (2 million) years ago
  • the Last Common Ancestor (LCA) of humans and neanderthals was 500 thousand years ago
  • the common ancestor of modern humans was 100 - 300 thousand years ago

Possible Appearance (Lineage Separation Event): 
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Female Iron Deficiency Likely


  1. Nutritional iron deficiency: an evolutionary perspective., Denic, Srdjan, and Agarwal Mukesh M. , Nutrition, 2007 Jul-Aug, Volume 23, Issue 7-8, p.603-14, (2007)
  2. Menstruation: a nonadaptive consequence of uterine evolution., Finn, C A. , Q Rev Biol, 1998 Jun, Volume 73, Issue 2, p.163-73, (1998)
  3. The evolution of endometrial cycles and menstruation., Strassmann, B I. , Q Rev Biol, 1996 Jun, Volume 71, Issue 2, p.181-220, (1996)
  4. Menstruation as a defense against pathogens transported by sperm., Profet, M , Q Rev Biol, 1993 Sep, Volume 68, Issue 3, p.335-86, (1993)