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"Menstruation: The Intriguing Key to Human Evolution"

"Unveiling the Secret Biological Strategy Behind the Monthly Cycle"

By Alisa İnnokatePublished 8 months ago 3 min read
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A unique and enigmatic phenomenon found in several species on Earth is the menstrual cycle, a trait that humans share with only a handful of other mammals. This group includes monkeys, apes, bats, and possibly elephant shrews, making us the exclusive members of the menstruating mammal club. What's even more intriguing is that we humans engage in this cycle more frequently than any other animal, despite its apparent inefficiency and inconvenience. So, why does this uncommon biological process exist? The answer is embedded in the intricacies of pregnancy.

Pregnancy is a remarkable biological process where a mother's body allocates its resources ingeniously to create a nurturing environment for a developing fetus, establishing an internal sanctuary for the growing child. However, this is only one side of the story. The less-known aspect of pregnancy reveals a fascinating conflict of interests between a mother and her unborn child. In the evolutionary pursuit of propagating their genes, the mother is naturally inclined to provide equally for all her offspring. However, a fetus doesn't inherit genes solely from its mother but also from its father. These paternal genes are motivated to secure their survival by extracting more than their fair share of resources from the mother. This evolutionary conflict sets the stage for a biological tug-of-war that unfolds within the womb.

A key player in this internal struggle is the placenta, a fetal organ that connects to the mother's bloodstream, nourishing the fetus as it grows. In most mammals, the placenta is concealed behind a maternal cell barrier, allowing the mother to regulate the supply of nutrients to the fetus. However, in humans and a select few other species, the placenta takes an extra step, infiltrating the mother's circulatory system to directly access her bloodstream. Through this specialized placenta, the fetus sends a cascade of hormones into the mother's arteries, ensuring a continuous flow of nutrient-rich blood. A fetus with such unrestricted access can manipulate hormone production to raise the mother's blood sugar, expand her arteries, and elevate her blood pressure.

Unlike most mammal mothers who can expel or reabsorb embryos if necessary, in humans, once the fetus establishes this blood connection, severing it can lead to potentially life-threatening hemorrhaging. If the fetus develops poorly or perishes, the mother's health is placed in jeopardy. As the fetus continues to grow, its persistent demand for resources can result in severe fatigue, high blood pressure, and conditions like diabetes and preeclampsia. Given these risks, pregnancy is an enormous, and sometimes perilous, investment. Hence, it becomes essential for the body to thoroughly vet embryos to determine which ones are worth this formidable challenge.

This is where menstruation enters the picture. The journey of pregnancy begins with a process called implantation, where the embryo embeds itself in the uterine endometrium. The endometrium has evolved to create an environment where only healthy embryos can successfully implant. However, this stringent selection process also favors the most aggressively invasive embryos, establishing an evolutionary feedback loop. The embryo initiates a precisely timed hormonal dialogue that transforms the endometrium to permit implantation.

But what happens when an embryo fails to meet the mark? It might still manage to attach or even partially penetrate the endometrium. As it slowly withers away, it can leave the mother susceptible to infections while emitting hormonal signals that disrupt her tissues. To circumvent this predicament, the body simply eliminates every potential risk. Each time ovulation doesn't culminate in a healthy pregnancy, the uterus sheds its endometrial lining, along with any unfertilized eggs and any sick, dying, or deceased embryos. This protective process is what we know as menstruation, leading to the monthly period. This seemingly unusual biological trait, as perplexing as it may appear, is a crucial element that ensures the continuation of the human race.

sciencehumanity
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About the Creator

Alisa İnnokate

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Nice work

Very well written. Keep up the good work!

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  • Mike Singleton - Mikeydred8 months ago

    Excellent article which I think many will find useful and informative

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