littlek
 
Reply Thu 17 Jun, 2010 07:01 pm
I was just talking with my housemate about primate fertility. (yes, I was). Wait, let me back-track and give you a glimpse into the workings of my brain.....

We were talking about religion and she said how Genghis Khan had it right - let the conquered keep their religions. Then I remembered something I heard recently about genetic testing in Asia and Eastern Europe which indicated the Genghis fathered MANY (ridiculously a lot) offspring which bear an indicator on their Y chromosomes. And I wondered about how we as animals ended up with this monthly ovulation when I couldn't think of any other animals that did this. My thoughts were that Genghis was somehow able to sense when women were ovulating and chose them for his sex-scapades lending to his high rate of fathering offspring. She said that she thinks we ovulate because we always have and our lives work in cycles. This didn't satisfy me, and I said that I thought primates didn't ovulate and we share 99.8+ of their DNA. Then I had to fact check. Primates do indeed ovulate on a (roughly) monthly cycle just as we do.

So, now the question remains - why? Do any other animals have this monthly cycle? Why did our little group go this route? What caused us to move from a more traditional mammalian cycle of a year to one of a month?
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talk72000
 
  1  
Reply Thu 17 Jun, 2010 07:02 pm
@littlek,
Primates include the clergy. The Church forbids Primates such as Bishops from marrying. Mr. Green
0 Replies
 
plainoldme
 
  1  
Reply Thu 17 Jun, 2010 07:22 pm
Here's a starting point but you may not want all this info . . . like the length of a orang-utan's menstrual cycle:

http://pin.primate.wisc.edu/aboutp/anat/menstrual.html
0 Replies
 
plainoldme
 
  1  
Reply Thu 17 Jun, 2010 07:25 pm
This is more interesting:

Some species, such as cats, cows and pigs, are polyestrous and can go into heat several times a year. Seasonally polyestrous animals or seasonal breeders have more than one estrous cycle during a specific time of the year and can be divided into short-day and long-day breeders:
Short-day breeders, such as sheep, goats, deer, foxes, elk—are sexually active in fall or winter.
Long-day breeders, such as horses and hamsters, are sexually active in spring and summer.
Species that go into heat twice per year, such as most dogs, are diestrous.
Monoestrous species, such as bears, foxes, and wolves, have only one breeding season a year, typically in spring to allow growth of the offspring during the warm season to survive the next winter.
A few mammalian species, such as rabbits do not have an estrous cycle and are able to conceive at almost any arbitrary moment.

It's from: http://en.wikipedia.org/wiki/Estrous_cycle

plainoldme
 
  1  
Reply Thu 17 Jun, 2010 07:25 pm
@plainoldme,
Melatonin is thought to be connected to estrus. Interesting.
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plainoldme
 
  1  
Reply Thu 17 Jun, 2010 07:26 pm
Still more:

Estrus frequencies of some other mammals:
Ewe: 17 days
Bovine: 21 days
Goat: 21 days
Sow: 21 days
Elephant: 16 weeks
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plainoldme
 
  1  
Reply Thu 17 Jun, 2010 07:32 pm
Anestrus refers to the phase when the sexual cycle rests. This is typically a seasonal event and controlled by light exposure through the pineal gland that releases melatonin. Melatonin may repress stimulation of reproduction in long-day breeders and stimulate reproduction in short-day breeders. Melatonin is thought to act by regulating hypothalamic pulse activity of gonadotropin-releasing hormone. Anestrus is induced by time of year, pregnancy, lactation, significant illness, chronic energy deficit, and possibly age.
talk72000
 
  1  
Reply Thu 17 Jun, 2010 07:39 pm
@plainoldme,
I guess they didn't know about the horny rabbits when they introduced them to Australia!
0 Replies
 
rosborne979
 
  1  
Reply Thu 17 Jun, 2010 08:20 pm
@littlek,
Interesting question.

Here's some stuff. I'm still researching...
Quote:
While the reasons behind why women menstruate remain unclear, research shows that the number of menstrual cycles modern women experience differs greatly from the number experienced by pre-agricultural women. It is impossible to know with certainty the reproductive patterns that prevailed 10,000 years ago. However, it is likely that the reproductive patterns of Stone Age women are more closely related to those of current hunter-gatherer societies than to those of western women (Eaton and Eaton III 1999). The best opportunity to study the natural pattern of human reproduction occurs with women in current foraging societies. American women currently experience three times as many menstrual periods as women who have continued living in the ways of earlier ancestors. Foraging women are 16 years old at menarche, 19.5 year old at first birth, nurse for three to four years, have a completed family size of 5.9 live births, and an average age at menopause of 47 years. They experience a total of 160 ovulations in their lifetime. Contemporary American women are 12.5 years old at menarche, 24 years old at age of first birth, nurse for 3 months (if at all), have a completed family size of 1.8, and are 50.5 years old at menopause. American women experience approximately 450 ovulations within their lifetime (Eaton et al 1994). A study done with the Dogon women of Mali shows a similar relationship. The Dogon are a foraging society that practices natural fertility by not using modern contraceptive methods. The Dogon have a fertility rate of 8.6 ± 0.3 live births per woman. Median number of lifetime menses experienced by the Dogon was 109, with a U-shaped relationship between menstruation and age showing that, from menarche to menopause, women in primary child-bearing years (20 —34 years old) rarely menstruated (Strassman 1999). Overall, this data indicates that monthly menstruation for decades on end is not the historical norm. Today, women have earlier menarche, later first birth, and fewer pregnancies. There is also a decreased suppression of menstruation through lactation as _ of children are never breast-fed and the rest only breast-feed for 3 months. Early menarche is an especially recent development. In the 19th century, the age of first menarche was the same as in the hunter-gatherer women observed today. The earlier age of first menarche can be linked to an increase in caloric intake, while at the same time occupational, educational, and social forces have led to a later first birth (Eaton and Eaton III 1999). The consequences for these changes in menstrual cycling may be seen in cancer rates among women in industrialized nations.


Source: http://webpub.allegheny.edu/employee/r/rmumme/FS101/ResearchPapers/RachelBayer.html
littlek
 
  1  
Reply Thu 17 Jun, 2010 09:16 pm
Fascinating, folks!
0 Replies
 
plainoldme
 
  1  
Reply Thu 17 Jun, 2010 09:43 pm
@rosborne979,
The increased menstruation of modern, urban women has to be related to their diet.

Consider that when sow bears go into estrus, they might be fertilized but unless their weight reaches a certain amount before they go into their winter sleep, the fertilized eggs will not implant. So, there is a connection between weight and conception. Light also matters. It looks like females have to be reasonably well fed and give birth at certain times of year.
dadpad
 
  1  
Reply Thu 17 Jun, 2010 11:41 pm
@plainoldme,
plainoldme wrote:

The increased menstruation of modern, urban women has to be related to their diet.

Yes i'd have to agree with that. Especially when you consider that poor diet and poor health can affect fertility evebn in modern/western societies.
0 Replies
 
rosborne979
 
  1  
Reply Fri 18 Jun, 2010 08:23 am
@plainoldme,
plainoldme wrote:
The increased menstruation of modern, urban women has to be related to their diet.

Then there's exercise and stress, too much of that and the cycle changes. And then there's fact that women in groups cycle together. A lot of factors seem to affect it.

I would think it's an evolutionary advantage for all females of every type (of mammal) to be fertile as much of the time as possible, so evolution probably pushes things in this direction. So there must be some selective mechanism in other mammals which presents a downside to that.

Most mammals our size are probably pushed toward a yearly cycle to allow the young to grow before starting the next generation. Small mammals like mice however can produce several generations per season.
plainoldme
 
  1  
Reply Fri 18 Jun, 2010 09:29 pm
@rosborne979,
You're right about fertility being an evolutionary advantage. Rabbits go into estrus with coitus and they are at the bottom of the food chain. I understand that the Holocaust survivors who stopped menstruating due to starvation, quickly became fertile again after the liberation of the camps.
0 Replies
 
dadpad
 
  1  
Reply Fri 18 Jun, 2010 09:45 pm
Quote:
I would think it's an evolutionary advantage for all females of every type (of mammal) to be fertile as much of the time as possible, so evolution probably pushes things in this direction. So there must be some selective mechanism in other mammals which presents a downside to that.

A lactating mother needs more food, so in grazing animals it would be an advantage to time estrogus to coincide the birth with spring. this would allow maximum milk production and maximum length of time to grow before the onset of harsher conditions in winter.
roger
 
  1  
Reply Fri 18 Jun, 2010 09:48 pm
@dadpad,
Around here, deer mate in the fall and birth in the spring.

Wait, that's what you just said.
0 Replies
 
talk72000
 
  1  
Reply Sat 19 Jun, 2010 01:15 pm
The easy living standards and the fatty foods offered by modern society probably helped in this matter not to mention the introduction of Playboy philosophy and the birth pill.
roger
 
  1  
Reply Sat 19 Jun, 2010 01:18 pm
@talk72000,
But the question is primate fertility. Do monkeys read Playboy? All of them, or just the males?
Rockhead
 
  1  
Reply Sat 19 Jun, 2010 01:20 pm
@roger,
yes, but just for the articles.
0 Replies
 
talk72000
 
  1  
Reply Sat 19 Jun, 2010 01:22 pm
@roger,
You seen the wild life in the bars after 12?
 

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