Tuesday, December 28, 2010

Book Review: Ancient Bodies, Modern Lives

Book Review of Ancient Bodies, Modern Lives: How Evolution Has Shaped Women’s Health by Wenda Trevathan. Oxford University Press, 2010

Through an exploration of the female reproductive life cycle from an evolutionary perspective, Wenda Trevathan’s book Ancient Bodies, Modern Lives shows the reader how such an approach can improve understanding of women’s health. Drawing on evolutionary medicine, she centers her investigation on the female reproductive life cycle in order to understand the implications of millions of years of evolution for modern women’s health. Her overall argument is for readers to take human evolutionary history, which is fundamentally about reproduction, into consideration when regarding modern women’s health issues. She organizes the book along the order of the female reproductive cycle, from menarche to menopause, concluding with a discussion of the implications for modern women’s health.  

The evolutionary medicine evaluation is a fascinating and unique approach to the topic of health. One key theme that the book addresses is the importance of life history theory and the idea of trade-offs. Life history theory predicts how and why humans adapt to their environments and societies by allocating energy to one thing and not to another (trade-offs) in order to increase reproductive success. Trevathan notes that despite the need for trade-offs, humans have the unique ability to maximize reproductive success, “through cultural interventions,” which she addresses throughout the book (13). In the discussion of every aspect of the reproductive lifecycle her consideration of the cultural, societal, and ecological impact on biology, and vice versa, is excellent.

Another key theme of the book is the mismatch between our evolved bodies and our present culture and lifestyles. For instance, she discusses how, as compared with most of human history, the onset of menarche now occurs earlier in health-rich nations. These women also become pregnant later and have fewer overall pregnancies and decreased breastfeeding rates, all for socio-cultural reasons. The result of this is a change in hormone levels present in the body over the lifetime, which has serious effects on health.  Age of first menarche, pregnancy and breastfeeding are all biological processes that have been shaped by evolution, but “evolutionary medicine and life history theory remind us,” that they are “sensitive to local environmental” and sociological situations (40).

Trevathan provides a captivating analysis of the medical implications for childbirth of the evolution of bipedalism and large brains and the trade-offs that must be made as a result. Walking upright meant a restructuring of the pelvis, which made it narrower than that of our ancestors and made fitting our larger brains much more difficult during childbirth. Furthermore, the shape of the pelvis changed so that the infant rotates more than once in order for the head and then the shoulders to make their way down into the birth canal. As a result, the baby is born facing the mother’s back, which makes it difficult for the mother to catch her own child without causing damage or death to the infant. Trevathan argues that this accounts for the nearly universal practice of having birth attendants present at birth to assist the mother in catching the baby.

Additionally, obstructed labor is becoming a problem for many women at time of birth, which contributes to the need for surgical delivery of the infant. One reason for this is the biomedical custom of giving birth in the lithotomy position, which is the least optimal position for birth. Also, women living in health-rich nations have increasingly larger babies, possibly due to higher body mass and/or diabetes. Trevathan notes, however, that Cesarean sections have a number of health risks for mother and child, such as increased respiratory distress in the infant. Children not born normally miss out on the many advantages of vaginal birth, many of which contribute to better mother-infant bonding. She argues persuasively that culture and our evolved bodies may not be the most compatible for optimal health.

The chapter on breastfeeding is one of the book’s most captivating. She writes about the myriad ways in which breastfeeding is one of the most important evolutionary adaptations for the survival of both mother and child after birth. Beyond the innumerable benefits for the infant, such as increased immune function and perfect nutrition, breastfeeding is also incredibly important for mothers. For one, newborns suckling immediately postpartum reduces the size of the uterus and prevents postpartum hemorrhage, which was especially important before the advent of biomedicine. Additionally, breastfeeding has lifelong positive effects on the mother’s health, such as lowered incidence of type 2 diabetes, osteoporosis, breast cancer, atherosclerosis, and more. So, Trevathan asks, why would anyone not breastfeed? This is where the sociocultural aspects come into play and Trevathan takes breastfeeding culture into account. She perceptively notes that, “‘breast is best’ is not sufficient in a culture that has devalued breastfeeding for two to three generations and where role models for successful breastfeeding have been rare” (125).

Though breastfeeding is an evolved biological process it, like mating and birthing, is culturally influenced. Trevathan recognizes that the reproductive life cycle of women is a process that is both deeply biological and cultural. This is what biocultural medical anthropology seeks to explore – the relationship between biology, health and culture. Biology and culture are mutually consequential. Though the book doesn’t delve too deeply into socio-political factors and their effect on health, I appreciate that Trevathan is cognizant of the fact that, “an evolutionary perspective tends to ignore some of the most important factors that impact women’s health – SES, cultural norms, education, media and peer influences [and] geopolitical forces” (191). While this is true, Trevathan does an excellent job explaining the link between evolutionary history and sociocultural context in most of the book. She acknowledges that though all reproductive life processes can be explained biologically we cannot stop the analysis there, or we would entirely miss what it means to be human.

This is a biological anthropology text that scholars in the field of medical anthropology would greatly benefit from. Medical anthropologists strive to dispel the myth that modern medicine adheres to:  that there is such thing as “normal” when it comes to human biology and health. This book also addresses the falsity of the concept of normal, as it aids in the quest to make medicine aware of the great amount of variability in “normal health” that exists among humans. Women growing up in health-rich nations have a different biological “normal” than women in health-poor nations, which may also be a different “normal” from the ancestral past. For instance, Trevathan explains that for some women a “normal” menstrual cycle is less than the typical 28 days in length as a result of having a different “normal” level of hormones. Thusly, the success of various methods of birth control, especially hormonal contraception, will differ. Furthermore, though the cessation of menses is a universal phenomenon, anthropologists have found that women in different cultures physically and psychosocially experience menopause differently than how biomedicine defines it. The evolutionary medicine lens assumes that humans are “highly diverse with a biology that unfolds in a context rather than in predictable unvarying ways” and that there is a “broad range within which growth and development can occur” (11-12).

A rich addition to the field of medical anthropology, Ancient Bodies, Modern Lives demonstrates that in an effort to understand and improve health we must look at health holistically. Just as medical workers should take into account cultural factors that affect health, so should cultural anthropologists take into account evolutionary history of women’s biology. Trevathan writes, “we are more likely to develop ways of promoting positive health if we know and understand…our evolved biology” (193). Moreover, it is an important book for medical and public health scholars, because of Trevathan’s perspective on the topic of “normal.” Health workers will learn from this book to look beyond the biomedical concept of normal and take cultural norms, socioeconomics and geopolitics into consideration when attempting to improve health.

The multitudes of examples in the book illustrate how millions of years of human evolution collide with modern-day environment and culture to create numerous health issues. But there are lessons to be learned as a result of Trevathan’s evolutionary medicine review of the female reproductive life cycle. We can get our evolved bodies and our lifestyles in tune if we follow prescriptions gleaned from this book, such as Trevathan’s advice to give birth in an upright position and to breastfeed our babies. Trevathan believes that if medical and lifestyle choices are made as a result of taking evolutionary processes into account, women’s overall health will be improved. This is one of the most important takeaways of the book – the fact that “we are more likely to develop ways of promoting positive health if we know and understand genetics and our evolved biology” (193). Despite its academic style, this is an excellent book for all women to read.

Overall, Wenda Trevathan’s book is a tremendous addition to the fields of biological and medical anthropology, especially in regards to women’s reproductive health. It is a compelling composition that thoroughly convinces the reader that in order to make improvements in health, we need to pay attention to what our evolved bodies are telling us.


Kim said...

I picked this up at the AAA this year and have big plans to start and finish it before the next semester starts. :-)

Thanks for the review!

Emily said...

I'm glad I could help - enjoy the book!

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