Here are two reasons that evolution and women's cycles go together.
First, from a theory developed by Leonard Shlain, in Sex, Time & Power, Gyna Sapiens (or women) were faced with an “evolutionary quandary” 150,000 years ago: birthing babies with heads so big they could tear them apart.
Being creative and resourceful, human females through evolution, adapted to having a monthly menses. We are the only female mammal to endure such frequent housecleaning, and the only one to experience orgasm and be sexually receptive all year round. If the pheromones are not right or if the mood strikes, we can also deny a male sex (thanks to a brain that can override sexual urges powered by instinct and hormones).
Our new big brains required a lot of oxygen, and with women losing blood periodically she needed a lot of iron. Ergo, she needed her man to hunt meat. Man gives woman meat, woman gives man sex.
Probably it was a woman who first connected the act of sex to the cessation of full-moon bleedings, followed by childbirth. (and the first to create calendars by marking this on a deer or antelope antler). She would have been the first to comprehend what Shlain calls deep-time, the ability to look to past and future, linking cause and effect: ‘having made this backward-looking link between sex and pregnancy, she peered more months into the future and realized that she had risked her life by engaging in sex.’
"A woman might have been first to contemplate death and to realize its inevitability, but when the men were clued in, they refused to go gently into that good night. It became a man’s priority to protect and provide for his own offspring so that he might live on through them. In short, they became husbands and fathers and patriarchs to boot.”
excerpted and adapted from from a review of Sex, Time & Power: How Women’s Sexuality shaped Human Evolution by Leonard Shlain, which appeared in the San Francisco Chronicle, written by Julie Mayeda , 2003
Here's another interesting fact about women's cycles: “Orangutans do not go into menopause. Chimpanzees do not need extract of mare pee. …Only in human females does the fertility program shut down years before death.” (Woman, An Intimate Geography, Natalie Angier)
Angier studied a tribe called the Hadza, from northern Tanzania, who are basically living as if they were still in the Stone Age. Here, the grandmothers help ensure the survival of young children so the mother can look after the newborns, by helping to gather food, clothe and protect, or babysit. Because of the long ‘childhood’ (until puberty, or age 13 on average) of humans, they need protection longer, and mothers need help, so they can forage, cook and clean. The grandmothers and aunts help not only their own grandchildren, but the children of anyone who needs it. Men’s hunting is not as reliable as foraging, and nursing women can’t forage very far, so grandmothers who are not lactating or birthing (in menopause) are crucial to tribe’s survival.
Besides which, the old wise women, with their accumulated knowledge of plants and dangers, and their long term memory, are a useful resource. “Before we could stay young, we had to learn to be old.” ie grandmothers invented youth. The brain could develop longer, because youth lasted longer, while granny fed the kids and helped mom have more kids, nurse them 2 years instead of 4-5 like chimpanzees, and the brains could grow and develop.
So there you have it, the case for menopause in evolution is that it frees up the grannies to babysit and forage for food, letting the human brain of babies grow for a longer period of time.
Wow, what a neat cycle!
see more articles on menopause (and poetry) at http://www.msmenopause.blogspot.com/