The human fetus is a greedy little creature. It competes with its mother for nutrients, oxygen, and blood. It latches its placenta onto the mother’s endometrium which is rich in blood and nutrients; it then immediately begins to control the mother’s blood supply and increase her blood sugar and blood pressure. It also uses the mother’s body to remove waste material from the embryo. It engages in a life-and-death struggle with the very entity that conceived it. It manipulates its mother in incredible ways, including playing with the hormonal system and even sending fetal cells into the mother’s own blood supply. It is a wonder that she even survives the process at all.
That may seem like overstating the case, but every year it is estimated that over 500,000 women in the world die in childbirth or during pregnancy, and that millions more are affected with injuries and disabilities due to pregnancy. Fully fifteen percent of women suffer complications from pregnancy that are life-threatening.
Other mammals do not have this problem. Pregnant females are able to carry on daily activities and even evade predators, give birth, and then get up and go about their business shortly thereafter. Human females, on the other hand, are an exception. the human fetus does what it can to control the mother. It is actually quite aggressive. Its placenta attaches itself to the mother’s endometrium and begins to commandeer her blood supply. The human mother’s endometrium is quite tough when matched against those of other mammals; it has to be, for the placenta is aggressive and will do all that it can to absorb as much of its mother’s blood as possible.
On one hand, the endometrium needs to restrict the intake of the fetus in order to protect the mother; on the other, the fetus needs to absorb as much blood and as many nutrients as possible in order to survive and thrive. It’s a struggle between two living creatures over the available food supply, and it’s this struggle that leads to complications during pregnancy, such as eclampsia (high blood pressure in the mother due to the excessive demands made on her blood by the fetus).
The human menstrual cycle is one result of this unique biological condition. While menstruation is not unique to humans, the toll it takes on the human female is considerably heavier. Other mammals experience menstruation, including primates as well as a type of bat; in the case of humans, however, the menstrual cycle carries with it a great variety of disorders from headaches and cramps to more severe bleeding, mood swings, etc. Thus a menstruating woman is clearly at a disadvantage when it comes to predators, so it would seem that evolution would not favor such a condition. Yet here we are.

Topics: life, babies, childbirth, cycling, illness, pregnancy, blood, death, hormones, Mammal, reproduction, menstruancy