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Menstruation: What is the evolutionary or biological purpose of having periods
I'm posting this because as far as I'm concerned the entire thing is a choice argument.
Inside the uterus we have a thick layer of endometrial tissue, which contains only tiny blood vessels. The endometrium seals off our main blood supply from the newly implanted embryo. The growing placenta literally burrows through this layer, rips into arterial walls and re-wires them to channel blood straight to the hungry embryo. It delves deep into the surrounding tissues, razes them and pumps the arteries full of hormones so they expand into the space created. It paralyzes these arteries so the mother cannot even constrict them.
What this means is that the growing fetus now has direct, unrestricted access to its mother's blood supply. It can manufacture hormones and use them to manipulate her. It can, for instance, increase her blood sugar, dilate her arteries, and inflate her blood pressure to provide itself with more nutrients. And it does. Some fetal cells find their way through the placenta and into the mother's bloodstream. They will grow in her blood and organs, and even in her brain, for the rest of her life, making her a genetic chimera.
This might seem rather disrespectful. In fact, it's sibling rivalry at its evolutionary best. You see, mother and fetus have quite distinct evolutionary interests. The mother 'wants' to dedicate approximately equal resources to all her surviving children, including possible future children, and none to those who will die. The fetus 'wants' to survive, and take as much as it can get. (The quotes are to indicate that this isn't about what they consciously want, but about what evolution tends to optimize.)
There's also a third player here – the father, whose interests align still less with the mother's because her other offspring may not be his. Through a process called genomic imprinting, certain fetal genes inherited from the father can activate in the placenta. These genes ruthlessly promote the welfare of the offspring at the mother's expense.
What this means is that the growing fetus now has direct, unrestricted access to its mother's blood supply. It can manufacture hormones and use them to manipulate her. It can, for instance, increase her blood sugar, dilate her arteries, and inflate her blood pressure to provide itself with more nutrients. And it does. Some fetal cells find their way through the placenta and into the mother's bloodstream. They will grow in her blood and organs, and even in her brain, for the rest of her life, making her a genetic chimera.
This might seem rather disrespectful. In fact, it's sibling rivalry at its evolutionary best. You see, mother and fetus have quite distinct evolutionary interests. The mother 'wants' to dedicate approximately equal resources to all her surviving children, including possible future children, and none to those who will die. The fetus 'wants' to survive, and take as much as it can get. (The quotes are to indicate that this isn't about what they consciously want, but about what evolution tends to optimize.)
There's also a third player here – the father, whose interests align still less with the mother's because her other offspring may not be his. Through a process called genomic imprinting, certain fetal genes inherited from the father can activate in the placenta. These genes ruthlessly promote the welfare of the offspring at the mother's expense.
http://www.quora.com/Menstruation/What-is-the-evolutionary-or-biological-purpose-of-having-periods/answer/Suzanne-Sadedin?srid=tsG0&share=1
4 replies
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= new reply since forum marked as read
Why is it that most female mammals go through a menstruation of sorts during estrus, while humans ovulate and menstruate at different times in their cycles. Is it the same with the great apes? I've never looked into it. Also, is it taken for granted that human females are more "receptive" during ovulation? I sure was. Lastly, are these stupid questions?
We've evolved sexually, although we are not the only creature to mate for pleasure and/or comfort. Some women seem to want to have sex more during ovulation, some don't.
This good info on the difference
Unlike many of our sisters in the animal kingdom, humans’ desire for sex isn’t restricted to fertile times, a trait we share with our close relatives the bonobos. Women and men alike usually desire sexual activity at any time of the month, not only when the woman is ovulating. However, studies have shown that many women experienced heightened sexual desires around the time of ovulation. Though there are no clearly visible signs of ovulation... women themselves usually do not know when they ovulate... humans experience estrous cycles. However, we call them by the name of their most visible component.
Fertility cycles in human women are called menstrual cycles. Though ovulation mostly passes invisibly, it is impossible for a woman not to notice when she has her period. This time of vaginal bleeding, which occurs once a month, usually lasts for close to a week. During menstruation, the woman sheds the lining of her uterus, which has built up over the previous month in anticipation of pregnancy. Menstruation typically does not happen if she is pregnant. The cycle is considered to start at the beginning of a menstrual period and end when the next one begins.
This is unique to humans. Most mammals reabsorb their uterine lining if they go through a fertility cycle without becoming pregnant. It is easy to tell when they are fertile, but not when their bodies are getting rid of unused uterine lining so as to build it up again in the next cycle. With humans, the opposite is true.
Fertility cycles in human women are called menstrual cycles. Though ovulation mostly passes invisibly, it is impossible for a woman not to notice when she has her period. This time of vaginal bleeding, which occurs once a month, usually lasts for close to a week. During menstruation, the woman sheds the lining of her uterus, which has built up over the previous month in anticipation of pregnancy. Menstruation typically does not happen if she is pregnant. The cycle is considered to start at the beginning of a menstrual period and end when the next one begins.
This is unique to humans. Most mammals reabsorb their uterine lining if they go through a fertility cycle without becoming pregnant. It is easy to tell when they are fertile, but not when their bodies are getting rid of unused uterine lining so as to build it up again in the next cycle. With humans, the opposite is true.
http://www.livinghealthy360.com/index.php/difference-between-menstrual-and-estrous-cycles-19544/
This is an interesting happening or it was for me once I identified it-- I never had "bad" periods, so I thought it was kind of cool. I'd just feel a sharp pain a dull ache and it was over. I could always tell which ovary released the egg. So many women have painful experiences in general, I always felt lucky.
Mittelschmerz (German: "middle pain"
is a medical term for "ovulation pain" or "midcycle pain". About 20% of women experience mittelschmerz, some every cycle, some intermittently.
Mittelschmerz is characterized by lower abdominal and pelvic pain that occurs roughly midway through a woman's menstrual cycle. The pain can appear suddenly and usually subsides within hours, although it may sometimes last two or three days.[1] In some cases it can last up to the following cycle. In some women, the mittelschmerz is localized enough so that they can tell which of their two ovaries provided the egg in a given month.[citation needed] Because ovulation occurs on a random ovary each cycle, the pain may switch sides or stay on the same side from one cycle to another.
Diagnosis of mittelschmerz is generally made if a woman is mid-cycle and a pelvic examination shows no abnormalities. If the pain is prolonged and/or severe, other diagnostic procedures such as an abdominal ultrasound may be performed to rule out other causes of abdominal pain.
http://en.wikipedia.org/wiki/Mittelschmerz
is a medical term for "ovulation pain" or "midcycle pain". About 20% of women experience mittelschmerz, some every cycle, some intermittently.
Mittelschmerz is characterized by lower abdominal and pelvic pain that occurs roughly midway through a woman's menstrual cycle. The pain can appear suddenly and usually subsides within hours, although it may sometimes last two or three days.[1] In some cases it can last up to the following cycle. In some women, the mittelschmerz is localized enough so that they can tell which of their two ovaries provided the egg in a given month.[citation needed] Because ovulation occurs on a random ovary each cycle, the pain may switch sides or stay on the same side from one cycle to another.
Diagnosis of mittelschmerz is generally made if a woman is mid-cycle and a pelvic examination shows no abnormalities. If the pain is prolonged and/or severe, other diagnostic procedures such as an abdominal ultrasound may be performed to rule out other causes of abdominal pain.
http://en.wikipedia.org/wiki/Mittelschmerz