Published Script

The Science Behind the Play

Evolution Is

Ten Great Advances in Evolution

The two women in The How and the Why are described as brilliant evolutionary biologists. While the characters Sarah Treem created are fictional, the theories they present are real. Controversial in their respective fields, the Grandmother Hypothesis and the Menstruation as a Defense theory are revolutionary and complicated and have affected how the scientific community perceives women and their bodies.

Please note: these theories are revealed over the course of The How and the Why so you may want to wait until after the production to read more about these radical ideas!

Grandmother Hypothesis

The Grandmother Hypothesis explains why a woman’s reproductive capabilities end considerably before her natural life.  Building on ideas first proposed by George C. Williams in 1957 and subsequently expanded and refined by other researchers, prominently recently by Kristen Hawkes, it suggests an evolutionary benefit in menopause for women, who can then focus all of their energy and resources on the survival of their existing children and grandchildren. This hypothesis has enormous implications on how humans developed apart from other primates. With older women assuming caretaking roles, offspring could stay weaker and more dependent for a longer period of time allowing their brains to develop.

Paradigm shifts are the stuff of scientific revolutions. They change how we view the world, the sorts of questions that scientists consider worth asking, and even how we do science. The discovery of DNA marked one such shift, the theory of plate tectonics another.

Douglas H. Erwin, The New York Times, 2007

“An end to a woman’s reproductive years allows her to channel her energy and resources into caring for her children and grandchildren, thereby providing her descendants with a survival advantage.”

“Evolution’s Secret Weapon: Grandma” The New York Times, Tara Parker-Pope (October 5,2007)

”A [post-menopausal] grandmother has a decidedly beneficial effect on the reproductive success of her children and the survival of her grandchildren … Women whose fertility is ending [have] an opportunity to influence the reproductive success of their daughters and survival of their grandchildren through assistance in food provisioning. In an ancestral population that was shifting from chimpanzee-like feeding to hard-to-handle foods, the more vigorous elder females could help more, thereby increasing the representation of their vigor in descendant generations, shifting rates of ageing, and lengthening average adult lifespans.”

“The Grandmother Effect” Nature, Kristen Hawkes (March 2004)

“Long post-menopausal lifespans distinguish humans from all other primates. This pattern may have evolved with mother-child food sharing, a practice that allowed aging females to enhance their daughters’ fertility, thereby increasing selection against senescence. … this hypothesis also accounts for our late maturity, small size at weaning, and high fertility. It has implications for past human habitat choice and social organization and for ideas about the importance of extended learning and paternal provisioning in human evolution.”

“Grandmothering, menopause, and the evolution of human life histories” The National Academy of Sciences, K. Hawkes, J.F. O’Connell, N.G. Blurton Jones, H. Alvarez, and E.L. Charnov (February 1998)

Menstruation as Defense

In her 1993 article, “Menstruation as a Defense Against Pathogens Transported by Sperm,” Margie Profet introduced the scientific community to a controversial new theory about the function of menstruation. According to Profet, women shed their uterine lining as a way to protect themselves from possible infection caused by pathogens introduced to the uterus by sperm. The body attacks this foreign matter in two ways: by shedding the lining of the uterus and washing it clean with blood rich with immune cells. This hypothesis was a radical shift in how menstruation is often perceived (many cultures consider it dirty and women on their periods are thought to be bad luck).

“Margie Profet of the University of California at Berkeley suggests that menstruation evolved as a mechanism for protecting a female’s uterus and Fallopian tubes against harmful microbes delivered by incoming sperm … The uterus is extremely vulnerable to bacteria and viruses that may be hitching a ride on the sperm, and menstruation is an aggressive means of preventing infections that could lead to infertility, illness and even death. In menstruation … the body takes a two-pronged attack against potential interlopers: it sloughs off the outer lining of the uterus, where pathogens are likely to be lingering, and it bathes the area in blood, which carries immune cells to destroy the microbes.”

“Radical New View of Role of Menstruation” The New York Times, Natalie Angier (September 1993)

“A new interpretation of menstruation sees it not as a passive loss of unused uterine lining but as an aggressive way to prevent infection by viruses and bacteria carried into the reproductive tract along with sperm. Menstruation sloughs off the potentially infected lining and bathes the area in blood carrying immune cells. The lining of the uterus is served by special spiral-shaped arteries that first constrict under hormonal stimulation, killing cells of the lining, and then dilate, creating a blood flow that washes the cells away. The protective theory is supported by the fact that there is a high concentration of disease-fighting macrophages in menstrual blood, which also lacks clotting factors, helping maintain the cleanup flow.”

“Radical New View of Role of Menstruation” The New York Times, Natalie Angier (September 1993)

“Sperm are vectors of disease. During mammalian insemination bacteria from the male and female genitalia regularly cling to sperm tails and are transported to the uterus … Menstruation functions to protect the uterus and oviducts from colonization by pathogens. Menstrual blood exerts mechanical pressure on uterine tissue, forcing it to shed, and delivers large numbers of immune cells throughout the uterine cavity, directly combating pathogens.”

    “Menstruation as a Defense Against Pathogens Transported by Sperm” The Quarterly Review of Biology, Margie Profet (September 1993)