The Evolutionary Significance of Female Menopause

Menopause is a universal phenomenon in humans alone, with occasional cases in domestic animals that seem to be “an artifact of civilization.”[1] Despite menopause being currently understood as a process separate from senescence due to its comparably more sudden onset, it is still difficult to separate menopausal changes from those of senescence. This means that identifying the biological start of menopause is equally, if not more, difficult, and the actual prompt for menopause is still debated. In spite of this, theories abound, and studies regarding the biological changes caused by and resulting in menopause are becoming more and more common. ­­In order to better understand why menopause would evolve in human females versus the world’s mammals, it is crucial to understand how menstruation evolved in the first place and how outside factors might affect the evolution of menopause.

            The two major theories regarding the evolution of menopause are Profet’s anti-pathogen hypothesis, and Strassman’s hypothesis that menstrual bleeding is a side-effect of endometrial regression. Marjorie Profet suggests that menstrual bleeding evolved as a means of cleaning the uterus and vagina of sperm-borne pathogens. She states that if this is the case, then uterine pathogens are more prevalent before menses than after, that menstruation tracks pathogen burden, and that the copiousness of menstruation increases with the promiscuity of the breeding system. In response to this hypothesis, Beverly Strassmann brings up several studies and experiments in which it was found that nutrient-rich blood only feeds bacteria, and brings up the cases of gonorrhea and Chlamydia, both of which are more prevalent after menstruation. She continues to say that menstruation does not track pathogen burden because women still have sex while pregnant, during post-partum amenorrhea, and in their postmenopausal years in both modern and preindustrial societies. Finally, Strassmann uses Profet’s own primate data to demonstrate a lack of correlation between promiscuity of the breeding system (different subspecies of macaques and baboons have different breeding systems and the same menstruation regardless).

Strassmann then proposes her own hypothesis that menstrual bleeding is a side effect of endometrial regression, which is more cost effective than maintaining the endometrium. She says that as women get closer to ovulation, the endometrium that lines the uterus is accompanied by the growth of an endometrial microvasculature that provides it with nourishment. When implantation does not occur, “then the endometrium actually erodes and its injured vasculature bleeds into the uterine cavity.”[2] Only 1/3 of the endometrium is shed – the rest, as in other primates – is reabsorbed. In healthy West European women, only 9% - 14% lose more than 80ml of blood, the threshold for iron deficiency in women, and the fecal protein loss over one cycle in women is higher than the menstrual protein loss over the same period, suggesting that it is not very costly to shed the endometrium.

Why would menopause be beneficial, given this information? Penn and Smith discuss the fitness costs of reproduction between the sexes, using “genealogical data from the Utah Population Database, for which survival information is complete for couples and their offspring.”[3] Using this data, they compared reproductive costs of men and women one year and five years after their last birth. They found that the survival rates of both parents decline with increasing parity during both intervals, and that increasing parity had a higher impact on the survival of the mothers than the fathers. This data suggested that “women had significantly higher risks of mortality than men at all levels of parity and worsened with increasing parity.”[4] The costs are persistent, and the more children that couples had, the higher the survival costs to both parents.

Penn and Smith made sure to control for socioeconomic status and other random effects, finding that the data was not confounded by outside variables. They also looked into survival of offspring based upon parental mortality, and found that the survival of the offspring was more dependent upon the survival of the mother than of the father. Their data also suggested that offspring reproductive success depends more upon the mother’s presence than the father’s, and is likely because mothers leave behind fewer surviving offspring (prudent mother hypothesis) as opposed to the enhancement of survival of grandchildren (grandmother hypothesis). This evidence provides an increasingly good evolutionary reason for menopause to exist in human females, but doesn’t explain the biological mechanism.

Wise et al. discuss two theories of causation of menopause: an unrenewable source of follicles in the ovaries, and the chemical interactions of the hypothalamus and ovaries. The first theory discusses how women are born with a certain number of follicles, and then explains that many will degenerate. In fact, there is a doubling of the “rate of loss of follicles in middle-aged women around the age of 35, when about 25,000 primordial follicles remain and, coincidentally, when perimenopausal symptoms begin to appear.”[5] This is a very common theory that is often discussed by the non-scientific community, but the second theory Wise et al. discuss also has substantial support. They mention that some investigators hold to the idea that the hypothalamus is what initiates the events leading to menopause, saying that changes that occur in the hypothalamus present themselves in women when they are between 35 and 40 years old, which is the same time that rates of follicular loss increase. The authors suggest that neither theory is mutually exclusive, and suggest that these processes may even occur independently of each other, while leading to the same end.

Leidy provides data that suggests that there is a genetic component to menopause in women who experience premature ovarian failure,[6] and that atresia (degeneration of the follicles) may be “an evolved mechanism that facilitates reproduction by means of relatively small numbers of offspring,”[7] – which would correlate to Wise et al.’s discussion of degeneration of follicles over time and correspond with Penn and Smith’s discussion of reproductive fitness costs on women with more offspring. I have also been able to relate Jared Diamond’s statement on offspring survival – “the birth of each child immediately jeopardizes the mother’s previous children due to increased risk of death in childbirth,”[8] – to Penn and Smith’s discussion of the same topic.

Other factors heavily influence when menopause occurs, as well. The median age of menopause in industrialized societies is roughly 47 – 51, where women are relatively well-nourished and have more of a choice in their pregnancies. In non-industrialized societies, this age is even younger.[9] Why? Penn and Smith suggest that fertility declines “are most closely linked to the improvements in women’s education and reproductive autonomy, suggesting that when given the opportunity, women prefer smaller families perhaps to reduce their costs (or perceived costs) of reproduction.”[10] The New England Research Institute, Leidy says, performed a study regarding women and smoking, and found that women who smoked not only have an earlier menopause, but also an earlier perimenopause.[11] Gillespie et al. found that women who are widowed early on have a higher chance of earlier menopause as well.[12] Lennon’s study (1982) discusses the psychological aspects of menopause and how it affects women, saying that when menopause is early or late, it causes psychological distress, but when it is on time (the years discussed above), “it is expected and appropriate.”[13] The influence of outside factors, then, can lead to psychological distress in women who are less healthy.

            Menopause, then, is a necessary factor. While it does not cost as much to shed the endometrium as it would to maintain it, the process of childbirth can be very stressful on the human body, and as parity increases, so too does the risk of survival for both the mother and her offspring. Smith writes that without menopause, women would “be forced to divide declining faculties between the care of extant offspring and increasingly hazardous production of new ones.”[14] Therefore, menopause is significant in the scope of human evolution in that it allows women to stop reproducing when it would risk their fitness and the survival of their offspring.

References:

Agee, Eve. "Menopause and the Transmission of Women's Knowledge: African American and White

Women's Perspectives." Medical Anthropology Quarterly, New Series 14, no. 1 (2000): 73-95.

Davis, Dona L.. "Blood and Nerves Revisited: Menopause and the Privatization of the Body in a

Newfoundland Postindustrial Fishery." Medical Anthropology Quarterly, New Series 11, no. 1

(1997): 3-20.

Diamond, Jared. Why is Sex Fun? The Evolution of Human Sexuality. 1^st ed. New York: Basic Books,

1997. Print.

Dillaway, Heather E.. "Menopause is the "Good Old": Women's Thoughts About Reproductive Aging."

Gender & Society 19, no. 3 (2005): 398-417.

Franceschi, Silvia, Demenico Schinella, Ettore Bidoli, Luigino Dal Maso, Carlo La Vecchia, Fabio

Parazzini, and Romano Zecchin. "The Influence of Body Size, Smoking, and Diet on Bone Density in Pre- and Postmenopausal Women." Epidemiology 7, no. 4 (1996): 411-414.

Gillespie, Duncan O.S., Mirkka Lahdenperä, Andrew F. Russell, and Virpi Lummaa. "Pair-Bonding

Modifies the Age-Specific Intensities of Natural Selection on Human Female Fecundity." The American Naturalist 176, no. 2 (2010): 159-169.

Leidy, L. E.. "Biological Aspects of Menopause: Across the Lifespan." Annual Review of Anthropology

23, no. (1994): 231-253.

Lennon, Mary C.. "The Psychological Causes of Menopauce: The Importance of Timing of a Life Stage

Event." Journal of Health and Social Behavior 23, no. 4 (1982): 353-366.

Nesse, Randolh M. and George C. Williams. Why We Get Sick, The New Science of Darwinian

Medicine. 1st ed. New York: Vintage Books, 1994. Print.

Penn, Dustin J. and Ken R. Smith. "Differential Fitness Costs of Reproduction between the Sexes."

Proceedings of the National Academy of Sciences of the United States of America 104, no. 2 (2007): 553-558.

Strassmann, Beverly I.. "The Evolution of Endometrial Cycles and Mentruation." The Quarterly Review

of Biology 71, no. 2 (1996): 181-220.

Williams, George C.. "Pleiotropy, Natural Selection, and the Evolution of Senescence." Evolution 11, no.

4 (1957): 398-411.

Winterich, Julie A.. "Sex, Menopause, and Culture: Sexual Orientation and the Meaning of Menopause

for Women's Sex Lives." Gender & Society 17, no. 4 (2003): 627-642.

Wise, Phyllis M., Kristine M. Krajnik and Michael L. Kashon. "Menopause: The Aging of Multiple

Pacemakers." Science, New Series 273, no. 5271 (1996): 67-70.

Zeserson, Jan M.. "How Japanese Women Talk about Hot Flushes: Implications for Menopause

Research." Medical Anthropology Quarterly, New Series 15, no. 2 (2001): 189-205.

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[1] Williams, George C., “Pleiotropy, Natural Selection, and the Evolution of Senescence,” p. 407.

[2] Strassmann, Beverly, “The Evolution of Endometrial Cycles and Menstruation,” p. 192.

[3] Penn, Dustin J. and Ken R. Smith, "Differential Fitness Costs of Reproduction between the Sexes,” p. 553.

[4] Ibid, p. 554.

[5] Wise, Phyllis et al, “Menopause: The Aging of Multiple Pacemakers,” p. 68.

[6] Leidy, L.E., “Biological Aspects of Menopause: Across the Lifespan,” p. 235.

[7] Ibid.

[8] Diamond, Jared, “Making More by Making Less: the Evolution of Female Menopause,” Why is Sex Fun?, p. 117.

[9] Leidy, L.E., “Biological Aspects of Menopause,” p. 240.

[10] Penn, Dustin J. and Ken R. Smith, "Differential Fitness Costs of Reproduction between the Sexes,” p. 553.

[11] Leidy, L.E., “Biological Aspects of Menopause,” p. 246.

[12] Gillespie, Duncan O.S. et al., “Pair-Bonding Modifies Age-Specific Intensities of Natural Selection on Human Female Fecundity,” p. 159.

[13] Lennon, Mary Clare, “The Psychological Consequences of Menopause,” p. 353.

[14] Smith, George C., “Pleiotropy, Natural Selection, and the Evolution of Senescence,” p. 408.

The Gebusi

Learning about another culture is always a rewarding experience, even when it is through the eyes of someone else. Bruce Knauft has given readers all over the world a lifetime opportunity in this regard, as the Gebusi people will never be the same as they are in the stories he has given us. Whether their changes are culturally for better or worse throughout time hardly matters; that they exist and have a culture to study is what is important. The intense speed at which Gebusi culture changed between 1982 and 1998 is unique, however, as globalization has shown a tendency in other cultures to take longer to turn a society around so much as it did the Gebusi. Incredible changes occurred especially in Gebusi customs of religion, marriage, sexual maturation, perceptions of time, and traditional rituals. In order to best understand how all of these things fit together in the Gebusi mindset, however, one must first consider the idea of kogwayay.

Kogwayay is a Gebusi concept that, on one hand, is the culture of the Gebusi while also, on the other hand, is impossible to define simply as ‘culture.’ Knauft writes that kogwayay is the idea of laughing and telling jokes loudly and happily together.[1] It is the backbone of Gebusi understanding of their culture, and truly it is present in all aspects of Gebusi culture. Traditions of séances, joking, and the intense camaraderie among Gebusi men encapsulate the idea of kogwayay. Every aspect of Gebusi culture comes full circle to kogwayay in one way or another, and thus it is extremely important to have even a slight grasp of this all-encompassing concept.

Gebusi religion in 1980 relied heavily upon the belief in spirits, especially those lusty female spirits whom would possess spirit mediums to charm men during séances. This belief in spirits and a further belief in sorcery created the fundamentals of Gebusi religious practices. A man or woman who died could be avenged if an investigation was launched (as often it was) to find the sorcerer who had afflicted the individual and killed them. The death rate among the Gebusi during this time was very high because of this, as few deaths were not attributed to sorcery. In 1998, Christianity came to Nomad and Gasumi Corners, paving the way for complete change in religious custom. Spirit mediums, such as Swamin, began to go to church, and held fewer and fewer spirit séances, until 1998 when they stopped occurring altogether. The door was shut on the spirit world, and access to the spirits of old was lost when the last spirit medium died and no more had been initiated. While Nolop knew how to hold a spirit séance, her status as a woman prevented her from ever truly becoming a spirit medium. Belief in God and Jesus had an incredible impact on Gebusi perspectives on death, however, as the Gebusi became more open to the idea of God taking the deceased unto him and into Heaven. Predictably, the homicide rates decreased significantly.

Marriage changed significantly, as well. While women were more prone to being given the freedom to choose their husbands in 1998, changes in the environment led to changes in the search for a wife. In 1998, Wayabay was the perfect Gebusi made for the 1980s. He was a traditionalist – hunting, gardening, and maintaining the old ways of life in the rainforest – and in a world that was trying to modernize, he was having extreme difficulties finding a woman who would have him as her husband. In 1980, this would not have been the case – Wayabay was strong, successful in his hunting, and a gentle person; he would have found a wife incredibly quickly following his initiation had he been of age in 1982. But in 1998, Knauft describes him as being the oldest of the bachelors, and actively looking to find a wife. The modernizing of Gasumi Corners, however, made it difficult for Wayabay to find a wife; hence his age and his desperation as he went to Bruce for help. Luckily for Wayabay, by 2001 he was married to Gami and eagerly awaiting his first child.

Related to marriage, sexual customs surrounding maturation changed dramatically in sixteen years. Boys were no longer being initiated into adulthood – a process that allowed for the easy selection of mates – and this meant that they no longer needed to be helped along in their growth by the men in the village. In 1980, Knauft observed that young, uninitiated males would often go off with initiated men for sexual trysts, the end goal being the consumption of the semen to give them enough to grow and become manlier, in effect increasing their own inherent maleness. Hawi and Doliay, neither of whom were initiated when Knauft first met them, partook in this custom, but also seemed to be incredibly involved with one another, even saying that they were never going to marry, as they had the other for sexual escapades. In 1998, these customs completely disappeared, replaced by religious teachings, practices, and the lack of passing the information on from the older generation to the younger. Sayu, Didiga, and Wayabay were completely unaware of these customs in 1998 until Knauft dropped the “cultural bomb” on them regarding the subject when Wayabay went to him for help.

The perception of time in Gebusi culture came into existence by 1998, with Gebusi all going to church, work, and school at the same times every day or every week. Dates appeared when discussing time and the past, something quite unusual to the Gebusi before then. In 1980, the idea of time was nowhere near as firm as it would become, with the Gebusi following more relaxed schedules that often revolved around how much work had to be done that day, and whether or not and major events were coming up. Dated years did not exist, and the concept of an hour was vague at best. The modernization of the culture in 1998 brought with it a stringent perception of time that was new to the Gebusi, as Knauft experienced when he was first invited to attend church with his friends, and found himself late due to following old Gebusi customs.

Traditional rituals were perhaps one of the most intensely changed. In 1980, traditions of the Gebusi were very important; initiations had to take place in just such a way, etiquette of visitors and then of hosts was very specific, etc;. When visitors came to Yibihilu, they traditionally displayed anger and aggression, which would be soothed and placated by the accommodating manner of the hosts, who would joke and then celebrate with the visitors in traditional Gebusi fashion. In 1998, during the Independence Day Festival at Nomad, visitors came from all over, but their aggression and anger was nowhere to be found in polite society. The Gebusi still played the gracious hosts, but the old traditions were gone, and it seemed to me that this new way was less warm and inviting and far more distant. Initiations in 1982 resulted in beautiful, meticulous costumes that sponsors contributed to, and spirit séances had as much a sacred and infallible air about them as they did a fun and joking air. The 1998 Independence Day Festival at Nomad also brought with it several plays and skits on the old customs – costumes looked vaguely similar to traditional wear, but were still very much costumes. The plays and skits exaggerated the “foolishness” of traditional ways, and poked fun at them in a manner that was widely accepted as comical. Knauft wrote that he had difficulty with these, because he was trained to respect the customs of other cultures, and yet was faced with the Gebusi mocking their own customs for all to see.

These examples are just a few out of many changes that occurred between the years 1982 and 1998, a sixteen year gap that would not have yielded such change in most other cultures. Of course, the Gebusi are not most other cultures, and are to be respected and appreciated for their own culture. Globilization dramatically changed Gebusi society by 1998, and the absence of government money by 2008 led to the furthered change of the Gebusi back towards their traditional heritage. They began to integrate the old and the new in a manner that was most fitting to their rainforest environment and continued survival as a people. Still Christian (the majority were Catholic), the homicide rate has remained remarkably low (no homicides occurred at all between 1998 and 2008), the sexual customs of maturation seem to remain dissipated, and the spirits remained closed-off from the Gebusi. However, the traditional methods of subsistence have remained, including farming and the half-domestication of wild pigs, and the Gebusi have built a new long house in Gasumi Corners, meaning that a new generation of Gebusi have been initiated.

The Gebusi have gone through globalization to a limited extent, and while many of the modern resources they had enjoyed in 1998 are no longer available to them, they have still maintained the things that they learned during that time, and have created yet another new culture for themselves that is very fitting for their history. They will never be able to return to their traditional ways ever again, simply because they have been influenced by many outside forces, particularly religion. Unique in their experience because of their voluntary contact with the outside world, the Gebusi have continued to change and grow as a society and as an indigenous people over the last thirty years in ways that no one could have predicted. Because of this, I greatly look forward to reading the next edition of Bruce Knauft’s The Gebusi, to see what gift he will give us next in teaching about the changes that have taken place among the Gebusi since 2008.

References:

Knauft,Bruce. The Gebusi: Lives Transformed in a Rainforest World. 2nd ed. New York:

McGraw-Hill, 2010.

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[1] Together referring primarily to men.

Concepts of Time

Douglas Raybeck contrasts Western ideas of time and the understanding of time among the villagers in Wakaf Bharu. The aborigines also share a different concept of time. Compare and contrast these three cultural settings of time and explain why you think variation occurs.

            As mentioned in the previous essays, language and culture influence each other to determine how we think about the world around us. Time is included in this viewpoint. In Western culture, time is viewed as occurring in a straight line, progressing from past to present to future, moving without change. For students in Western cultures, perceiving time as anything but a forward progression can be incredibly difficult, because our language and culture reinforces this idea so strongly. Not only that, but American culture specifically is very concerned with timing as well. Punctuality is a highly coveted attribute. We adhere to rigid schedules that determine when we must go to work, go to class, visit the doctor, etc;. We make appointments for nearly everything. In fact, one could view a class schedule as consisting of several pre-scheduled appointments.

            All Kelantanese, according to Raybeck, and the villagers of Wakaf Bharu specifically, have a much looser, present-time oriented understanding of time in which schedules are flexibly scheduled around the Islamic prayer times, which are themselves flexibly scheduled around the work schedule. This seems confusing at first, but really only demonstrates how ultimately unimportant time is in Wakaf Bharu culture when compared to Western culture. Activities that must be done are not hastened, but leisurely completed at the pace of the villager, as he or she is able to accomplish them. As Raybeck learned, scheduling an appointment with a villager could result in the villager appearing anywhere from half an hour early to two hours late, this range appearing to be culturally accepted as punctual.

            However complicated the idea of time may seem in Wakaf Bharu, it is even more complicated among the aborigines of Australia, at least at first glance. According to the aborigines, there is no past, present, or future, but rather all of time occurs simultaneously, operating together. Part of this is because of the aboriginal concept of the Dreaming, the time period spanning the beginning of all time to the time right before human memory. The Dreaming encompasses everything in the cosmos, including time. Through the Dreaming, all things work in concert and are completely integrated, and from this we can see clearly where this integrated, simultaneous nature of time originated.

            These three very different perspectives of time are very interesting to compare and contrast. Why did these ideas of time evolve the way in which they did? Variation in beliefs and ideas in human beings is often the result of regional, economic, and industrial factors. For instance, peasant villages like Wakaf Bharu have a smaller, more limited economy than many of the first-world Western cultures. They also lack many of the industrial benefits – which we think of as being modern – of those cultures. The aborigines are the same, but their regional history differs from that of Wakaf Bharu in that they existed largely isolated until the 1800s, uninfluenced by other cultures, while the Kelantanese did not have that luxury.