This is very private. But it is not shameful or unwelcome when it comes to health and wellbeing on a larger scale. It is a natural biological process. But when in the eyes of a beholder it becomes a taboo that affects relationships, inculcates fears, creates involuntary physical emotions, then “overcoming taboos becomes an enlightening duty” (Heinzpeter Znoj).
We are talking about menstruation.
This remarkable phenomenon, when explored further as part of life's journey, enhances our understanding of human existence, revealing insights into our fragility and prompting reflection on life choices for both men and women.
“Ad bellum”: collision over power and resources
Look at this picture.
From left to right you can see: (A) chimpanzee (B) spiny mouse, (C) short-tailed fruit bat C. perspicillata; (D) elephant shrew.
These are the only species on earth that have menstruation. And humans.
Why only us?
In the book “A Brief History of the Female Body: An Evolutionary Look at How and Why the Female Form Came to Be” released last December, its author - the evolutionary geneticist Dr Deena Emera - explains this with a few striking insights that show what we have in common:
Our motherhood is tough: we produce 1-2 kids in which we invest a lot of energy, bear rather high miscarriage rates and quite a high percentage of poor embryos. In humans, the latter is intertwined with "hidden" ovulation, impacting the consistency of intimate relationships throughout the cycle, unlike animals with distinct mating periods. This physical communication pattern in humans in turn plays a pivotal role in strengthening bonds within monogamous couples, shaping our evolutionary journey.
Unusual endometrium: in contrast to other mammals, the endometrium (the inner epithelial layer of the mammalian uterus), undergoes hormone-induced spontaneous decidualization (SD) once per cycle and involves wounds, blood, and the risk of infection. It occurs to prepare a conducive environment for pre-impregnation while filtering out the poor embryos. Here’s a bonus finding here: those species who prevent invasion of placenta also are immune to cancer.
Biological evolutionary conflict: it is a pretty bloody affair that takes three to tango.
maternal-fetal conflict over resources: this conflict arises from the invasive nature of our placenta. Our babies are very demanding. During pregnancy, the placental tissues penetrate the endometrium, opening the mother's blood vessels and enabling the fetus to assert control by releasing hormones into her bloodstream. Good examples of this conflict are complications pertinent to the third trimester such as gestational diabetes (fight for sugar) or preeclampsia (fight of blood).
mom-dad collision over power: it is about genomic imprinting - a process where certain genes inherited by a child are "silenced" by both parents. Mothers suppress genes promoting excessive baby growth to reserve resources for potential future pregnancies. In contrast, paternal genes advocate for maximal resource allocation to the current baby, considering the lower likelihood of the same father having his next baby in the same female body again.
En bref, menstruation has a very important evolutionary purpose. This mechanism likely evolved as a sophisticated quality control system for screening embryos in our ancient past. Over time, it became a permanent feature, triggered not only in response to embryo issues but also preemptively.
“M” for mice
The “M” phenomenon started getting more attention when women joined scientific troops at the beginning of the XXth century. Dr Meredith Runner from the Jackson Lab in Maine, US, was among the female pioneers to understand the delicate nature of the endometrium.
Her groundbreaking work involved harvesting mouse eggs from the eyes of white mice, which were transparent enough to observe fetal development. Surprisingly, embryos thrived when attached to the iris, feeding on blood vessels, instead of the uterus where rejection was common. This discovery highlighted the fetus's ability to establish its blood supply in a comfortable environment, offering valuable insights into abdominal pregnancy phenomena.
Dr Runner described her experiment in 1947 in Anatomical Records. This was, perhaps, the first illustration of a maternal-fetal conflict: a fetus invasion and the female body’s reaction to defend itself.
As later observed by Dr David Heig, evolutionary biologist from Harvard University, in most mammal species placentas are non-invasive: the embryo cells do not "crawl" inside the mother’s vessels and don’t "change the code".
Menstruation and the life course
The journey of human life commences long before birth, with menstruation signaling the body's readiness to embrace new life.
Prioritizing menstrual health is integral to effective obstetric management, beginning from early pregnancy.
This demanding phase requires both mother and child to navigate a delicate balance between survival and cooperation, underscoring the importance of comprehensive maternal and fetal care.
Recognizing the high value of this process is key, as both men and women embark on a challenging yet thrilling journey through life, whether or not they become parents. This path is characterized by external challenges and internal conflicts driven by the perpetual clashes of maternal and paternal genes—a fundamental aspect of natural evolutionary processes that we still need to continue studying and understanding. It is natural.
Why do we talk about the “M” phenomenon now?
For us, in ÆRAS, thinking in a tripartite "health-education-heritage” paradigm is our raison d’être. The “M” case is a clear illustration of the importance of this approach. This is how - we believe - important public health decisions should be made. With a clear understanding of our evolutionary heritage and of the historic pain of societal dramas.
The first International Conference on Population and Development held in Cairo, Egypt in 1994 has had a significant impact on shaping the global approach to sexual and reproductive health. Three decades of progress and setbacks later, the World Health Organization (WHO) emphasizes again key components of comprehensive sexual and reproductive health and rights, this time in the light of equality and dignity.
Menstrual health is one of them.
It is quite important for making informed choices and navigating life’s challenges - this understanding of the value and the origins of the pain and struggle that accompany us all throughout our life course ... A big part of our evolutionary heritage …
We leave this here for reflections, internal dialogues, and, perhaps, some change.
Related: ÆRAS Life Course, ÆRAS Heritage Research,
References:
Narasimhan M, Say L, Allotey P. Three decades of progress and setbacks since the first international conference on population and development. Bull World Health Organ. 2024 Apr 1;102(4):226-226A. doi: 10.2471/BLT.24.291654. PMID: 38562203; PMCID: PMC10976866. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10976866/
Emera, Deena. A Brief History of the Female Body: An Evolutionary Look at how and why the Female Form Came to be. Sourcebooks, Inc., 2023.
Babbar, Karan, et al. "Menstrual health is a public health and human rights issue." The Lancet Public Health 7.1 (2022): e10-e11. https://www.thelancet.com/journals/lanpub/article/PIIS2468-2667(21)00212-7/fulltext
Haig, David. "Cooperation and conflict in human pregnancy." Current Biology 29.11 (2019): R455-R458. https://www.sciencedirect.com/science/article/pii/S0960982219304385
Catalini, Laura, and Jens Fedder. "Characteristics of the endometrium in menstruating species: lessons learned from the animal kingdom." Biology of Reproduction 102.6 (2020): 1160-1169. https://academic.oup.com/biolreprod/article/102/6/1160/5775593
Kshitiz, et al. "Evolution of placental invasion and cancer metastasis are causally linked." Nature ecology & evolution 3.12 (2019): 1743-1753. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7340496/
Macklon, Nick S., and Jan J. Brosens. "The human endometrium as a sensor of embryo quality." Biology of reproduction 91.4 (2014): 98-1. https://www.researchgate.net/publication/265344341_The_Human_Endometrium_as_a_Sensor_of_Embryo_Quality
Runner, Meredith N. "Development of mouse eggs in the anterior chamber of the eye." (1947): 1-17.
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