by
Thea Monique Lamoureux
Bachelor of Arts (distinction), University of Victoria, 2013
A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of
MASTER OF ARTS
in the Department of Anthropology
©Thea Monique Lamoureux, 2019 University of Victoria
All rights reserved. This thesis may not be reproduced in whole or in part, by photocopy or other means, without the permission of the author.
Supervisory Committee
Difficult and Deadly Deliveries?: Investigating the presence of an ‘obstetrical dilemma’ in Medieval England through examining health and its effects on the
bony human pelvis
by
Thea Monique Lamoureux
Bachelor of Arts (distinction), University of Victoria, 2013 Supervisory Committee
Dr. Helen Kurki, Co-‐Supervisor (Department of Anthropology)
Dr. Erin McGuire, Co-‐Supervisor (Department of Anthropology)
Abstract
Difficult human childbirth is often explained to be the outcome of long-‐term evolutionary changes in the genus Homo resulting in an ‘obstetrical dilemma,’ defined as the compromise between the need for a large pelvis in birthing large-‐
brained babies and a narrow pelvis for the mechanics of bipedal locomotion (Washburn, 1960). The ‘obstetrical dilemma’ is argued to result in the risk of cephalopelvic disproportion and injury (Washburn, 1960). Current research challenges the premise of the obstetrical dilemma by considering the effects ecological factors have on the growth of the bony human pelvis (Wells et al., 2012; Wells, 2015, Stone, 2016; Wells, 2017). This thesis tests Wells et al.’s (2012)
assertion that environmental factors, such as agricultural diets, compromise pelvic size and morphology and potentially affect human childbirth. The skeletal samples examined in this study are from medieval English populations with long-‐established agricultural diets. Bony pelvic metrics analyzed are from the St. Mary Spital
assemblage, and demographic and pathological data from St. Mary Spital were compared to the East Smithfield Black Death cemetery assemblage. The results show that there is some evidence for a relationship between chronic stress and compromised pelvic shape and size in both men and women, however the evidence is not conclusive that younger women with compromised pelvic dimensions were at an increased risk of obstructed labour and maternal mortality during childbirth. This suggests that childbirth was not likely a significantly elevated cause of death among younger women in medieval London as a result of cephalopelvic
disproportion. The concept of a single obstetrical dilemma is flawed, as multiple obstetrical dilemmas other than cephalopelvic disproportion through pelvic capacity constrains are present, including ecological and nutritional stressors, childbirth practices and technologies, sanitation practices, and social and gender inequality.
Table of Contents
Supervisory Committee ... ii
Abstract ... iii
Table of Contents ... v
List of Tables ... vii
List of Figures ... x
Acknowledgements ... xii
Dedication ... xiii
1 Background ... 1
1.1 Introduction ... 1
1.2 Evolution and the Human Childbirth Process ... 3
1.3 The Environment and Obstetric Risk ... 10
1.4 Cephalopelvic Disproportion ... 14
1.5 Nutrition, the Skeleton, and Population Demographics ... 18
1.6 Medieval England and Dietary Deficiency ... 21
1.7 Medieval English Diet ... 23
1.8 Research Significance ... 28
2 Materials and Methods ... 30
2.1 Materials ... 30
2.1.1 St. Mary Spital ... 32
2.1.2 East Smithfield Black Death Cemetery ... 38
2.2 Methods ... 40
2.2.1 Osteometric Variables ... 41
2.2.2 Stature and Body Mass ... 45
2.2.3 Pathological Data ... 45 2.3 Statistical Analysis ... 47 2.3.1 Intra-‐Observer Analysis ... 47 2.3.2 Univariate Analysis ... 48 2.3.3 Bivariate Analysis ... 49 2.3.4 Multivariate Analysis ... 49
2.4 Hypotheses and Predictions ... 51
3 Results ... 54
3.1 Intra-‐Observer Analysis ... 55
3.2 Age Distribution ... 55
3.3 Stature and Body Mass Estimates ... 56
3.4 Paleopathological Indicators ... 59
3.5 Size and Shape of the Pelvis ... 60
3.5.1 Pelvic Size and Shape in the St. Mary Spital Sample ... 60
3.5.2 Skeletal Health Indicators and Pelvic Size and Shape ... 66
3.5.3 Pelvic Size and Shape in Relation to Body Size ... 71
4 Discussion ... 78
4.1 Age Distribution ... 78
4.2 Stature and Body Mass ... 79
4.3 Paleopathological Indicators ... 79
4.4 Size and Shape of the Pelvis ... 80
4.4.1 Pelvic Size and Shape in the St. Mary Spital Sample ... 80
4.4.2 Skeletal Health Indicators and Pelvic Size and Shape ... 87
4.4.3 Pelvic Size and Shape in Relation to Body Size ... 88
5 Conclusion ... 90
5.1 Directions for Future Research ... 93
5.2 Conclusion ... 94 References Cited ... 96 Appendix A. ... 105 Appendix B. ... 107 Appendix C. ... 108 Appendix D. ... 109
List of Tables
Table 1.1. Incidence of selected conditions (per million) related to pregnancy and/or birth among women in various regions of the world as reported by the WHO in 2004 (adapted from Mathers et al., 2008:28). An entry of 0.0 in the table refers
to an incidence of less than 50 000. ... 15
Table 2.1. Comparison of St. Mary Spital and East Smithfield Black Death sample sizes. ... 31
Table 2.2. Categories of ages-‐at-‐death for examination of population demographics in this project. [Source: adapted from Powers, 2007:8-‐9]. ... 31
Table 2.3. St. Mary Spital burial periods and date ranges, as defined by Connell et al. (2012:xix). ... 41
Table 2.4. Measurements and their corresponding descriptions for calculating pelvic canal dimensions, body mass, and stature (see also Figure 2.1). [Source: measurement definitions from Kurki, 2013b:798]. ... 42
Table 2.5. Stature and body mass estimation formulae derived from Ruff et al. (2012). Femoral length (FML) is measured in cm while femoral head diameter (FHD) is measured in mm (Ruff et al., 2012). ... 45
Table 3.1. Summary statistics for St. Mary Spital females (n=21). ... 54
Table 3.2. Summary statistics for St. Mary Spital males (n=19). ... 54
Table 3.3. Frequency statistics for age categories in the St. Mary Spital sample. ... 54
Table 3.4. Frequency statistics for age categories for the random selection of individuals from St. Mary Spital and East Smithfield Black Death used in Mann-‐ Whitney U-‐Tests. ... 56
Table 3.5. Mann-‐Whitney U-‐Test results. ... 56
Table 3.6. Summary statistics for body mass estimates in the St. Mary Spital and East Smithfield Black Death samples for individuals with FMHD data available. ... 57
Table 3.7. Frequency statistics for age categories of individuals selected for body mass estimation in the St. Mary Spital and East Smithfield Black Death samples. ... 57
Table 3.8. Summary statistics for stature estimates in the St. Mary Spital and East Smithfield Black Death samples for individuals with FML data available. ... 57
Table 3.9. Frequency statistics for age categories of individuals selected for stature estimation in the St. Mary Spital and East Smithfield Black Death samples. ... 58
Table 3.10. Descriptive statistics of stature estimations for independent samples t-‐ test results in Table 3.11. ... 58 Table 3.11. Independent samples t-‐test results for females and males examining
Table 3.12. Descriptive statistics of body mass estimations for independent samples t-‐test results in Table 3.13. ... 59 Table 3.13. Independent samples t-‐test results for females and males examining
body mass between the St. Mary Spital and East Smithfield Black Death
samples. ... 59 Table 3.14. Summary data for chronic stressors in both the St. Mary Spital and the
East Smithfield Black Death samples. ... 60 Table 3.15. Relative risk for having evidence of chronic stress within and between
the St. Mary Spital (SMS) sample and the East Smithfield Black Death (ESBD) sample. ... 60 Table 3.16. Eigenvector coefficients for principal components of pelvic shape
among males and females in the St. Mary Spital sample. ... 61 Table 3.17. Summary statistics for principal components shown in Table 3.18,
separated by males and females. ... 62 Table 3.18. Descriptive statistics for females in independent samples t-‐test results in Table 3.19. ... 65 Table 3.19. Independent samples t-‐test results for female pelvic size (geometric
mean) and pelvic shape (principle components) among young adults and
middle/older adults in the St. Mary Spital sample. ... 65 Table 3.20. Descriptive statistics for males in independent samples t-‐test results in
Table 3.21. ... 65 Table 3.21. Independent samples t-‐test results for male pelvic size (geometric mean)
and pelvic shape (principle components) among young adults and
middle/older adults in the St. Mary Spital sample. ... 66 Table 3.22. Frequency statistics for age categories of individuals selected for
assessment of LEH, PH, and CO from the St. Mary Spital and East Smithfield Black Death samples. ... 67 Table 3.23. Frequency statistics for LEH, PH, and CO in select individuals from the St.
Mary Spital and East Smithfield Black Death samples (0 = absent; 1 = present). ... 67 Table 3.24. Descriptive statistics for independent samples t-‐test results in Table
3.25. ... 68 Table 3.25. Independent samples t-‐test results for females and males examining the
difference between LEH, PH, and CO and pelvic shape in the St. Mary Spital sample. ... 69 Table 3.26. Descriptive statistics for independent samples t-‐test results in Table
Table 3.27. Independent samples t-‐test results for females and males examining the difference between LEH, PH, and CO and pelvic size in the St. Mary Spital
sample. ... 70 Table 3.28. Results of Pearson correlation test for stature, body mass, pelvic canal
size, and pelvic canal shape (PC1, PC2, and PC3) in females from St. Mary Spital. ... 72 Table 3.29. Results of Pearson correlation test for stature, body mass, pelvic canal
size, and pelvic canal shape (PC1, PC2, and PC3) in males from St. Mary Spital. ... 72 Table 4.1. Pelvic shape features of sexual dimorphism observed in PC1 and PC2
between females and males, ages combined, from the St. Mary Spital sample. . 81
List of Figures
Figure 1.1. The relationship between the size of a human neonatal cranium and the maternal pelvic inlet (bottom right) compared to other primate species
(Source: Rosenberg and Trevathan, 2002:1200). ... 6 Figure 1.2. Comparison of the birth mechanisms of Chimpanzees (left),
Australopithecus (middle), and modern humans (right). Note the rotational birth mechanism in humans (Source: Rosenberg and Trevathan, 2002:1204). ... 8 Figure 1.3. The pelvic inlet, midplane, and outlet. The first image, ‘a,’ illustrates the
pelvic inlet from a superior view, while from a posterior view, ‘b’ illustrates the midplane and ‘c’ illustrates the outlet. [Source: adapted from Kurki,
2013b:797]. ... 9 Figure 2.1. Pelvic measurements as referenced by Table 2.4. [Source: adapted from
Kurki, 2013b:797]. ... 43 Figure 2.2. Masking tape used to rearticulate the acetabulum of context 8781. Only
broken bones with a clean fit were rearticulated using masking tape. ... 44 Figure 2.3. Articulated pelvis of context 23735 using masking tape and elastic bands.
... 44 Figure 2.4. Difference between cribra orbitalia (left, blue arrow), as seen in a 4-‐year-‐
old XII Dynasty child from Lisht Egypt, and porotic hyperostosis (right, red arrow), as seen active in a 3-‐year-‐old Native American child from Pueblo Bonito, New Mexico (AD 950-‐1250) (top) and healed in an unprovenienced anatomical specimen. [Source: Walker et al., 2009:110]. ... 47 Figure 3.1. Scatter plot illustrating PC1 and PC2 as representative of sexual
dimorphism in the sample. Note the clustering of females to the bottom center-‐ left and the clustering of males to the top center-‐right. ... 63 Figure 3.2. Scatter plot illustrating PC1 and PC3. Note a weak presence of clustering
of males in the upper right quadrant and females in the lower left quadrant. .. 64 Figure 3.3. Scatter plot of St. Mary Spital females PC scores of PC1 and PC2 marking
the presence and absence of LEH. Note the clustering of females with the
presence of LEH along PC1. ... 71 Figure 3.4. Scatter plot of pelvic canal size and stature for males and females in the
St. Mary Spital sample. ... 73 Figure 3.5. Scatter plot of pelvic canal size and body mass in both males and females
in the St. Mary Spital sample. ... 74 Figure 3.6. Scatter plot of PC2 (representing sexual dimorphism) and stature for
both males and females in the St. Mary Spital sample. ... 75 Figure 4.1. Scatter plot of PC1 and PC2 for St. Mary Spital females. Note weak
Figure 4.2. Scatter plot of PC1 and PC2 for St. Mary Spital males. ... 83 Figure 4.3. Scatter plot of PC1 and PC3 for St. Mary Spital females. Note weak
clustering of younger females in the bottom right quadrant. ... 85 Figure 4.4. Scatter plot of PC1 and PC2 for St. Mary Spital males. ... 86
Acknowledgements
I would like to thank Sarah-‐Louise Decrausaz, Emma Blinkhorn, Kristianne Anor, and Melanie Callas for always being there for me when I needed an editor, opinion, or advice. I would also like to express gratitude to my three Maids of Honour – Katie Mutrie, Lia Butler (Bogachek), and Kirsty Callagher – for supplying me with the friendship and humour I have needed over the last few years while completing this study.
I’d further like to extend my thanks to my graduate supervisors Dr. Helen Kurki and Dr. Erin McGuire, both whom have been very supportive of me and believed in my capabilities, even when I surprised them with the news of my pregnancies. I am overwhelmingly appreciative of their patience in allowing me to take my time to raise my children while writing this thesis. Never once did I feel pressured to make a choice between my family and my passion, and for that I am ever indebted. Also, thank you to my external supervisor, Dr. Amy Scott, who provided valuable feedback on this thesis.
I am grateful for receiving a research grant from the Social Sciences and Humanities Research Council of Canada, and for the scholarships and funding I received from the University of Victoria. These funding sources made this project possible.
Thank you to Jelena Bekvalac and Dr. Rebecca Redfern at the Museum of London for being so accommodating during my research. I appreciate their help doing the heavy lifting of the boxes, as I was pregnant with Alice, and for going back and forth to the rotunda multiple times to bring me more specimens to examine. Also, thanks for all of the snacks and sweets!
Many thanks to Dr. Sharon DeWitte, who was kind enough to share her pathological data on the East Smithfield Black Death sample with me. This enabled me to conduct some tests that I otherwise would have been unable to do.
I must also express my appreciation to my employer Millennia Research Ltd., namely Morley Eldridge and D’Ann Owens, whom have taught me so much about archaeological analysis and writing, and have given me the opportunity to continue to learn. Morley and D’Ann hired me as an archaeologist knowing I had little
experience in BC coastal archaeology, and were willing to give me the chance to prove myself capable of the position. I can only hope that I am succeeding. Most of all, I’d like to thank my family – my grandparents for watching the kids while I battled with SPSS at the university, my mother-‐in-‐law for entertaining the baby while I tried to type a few sentences here and there, and my mother for her enthusiasm in telling strangers about my academic and career pursuits.
Of course, I could not thank my fiancé and children enough – Jeremy (Jay) Sawin for miraculously still loving me; my beautiful, stubborn, charismatic, and witty child Alice Lily Sawin; and my sweet, precious baby Odessa Ivy Sawin. My daughters taught me the most intimate, intricate first-‐hand details about the process of childbirth, intensifying my desire to learn more; Jay did the laundry and cooked dinner without me pestering him.
Dedication For:
Alice, Odessa, and whomever else I may one day be fortunate enough to call my child.
1
Background
The aim of this thesis is to test the assertion by Wells et al. (2012) that ecological factors, such as nutritionally deficient agricultural diets, compromise pelvic shape and size and potentially increase or decrease the risk of injury or death during childbirth. This is achieved by examining a population at a particular point in time in order to understand obstetric risk in specific ecological contexts. Existing explanations for the risk of injury or death during birthing are then reconsidered through demographic evidence concerning differential mortality relating to childbirth and biological plasticity in a population, specifically a medieval English agricultural society where nutritional deficiencies may have affected bone growth.
1.1 Introduction
Compared to other animals and primates, humans have a particularly difficult childbirth process that is both complex and physically painful (Rosenberg and Trevathan, 2002). This difficult childbirth process is often explained to be the
outcome of long-‐term evolutionary changes in the genus Homo resulting in the ‘obstetrical dilemma’ (Washburn, 1960; Wittman and Wall, 2007; Wells et al., 2012). The obstetrical dilemma is a concept explained as the compromise between the need for a large pelvis in birthing large-‐brained babies and the need for a narrow pelvis for the mechanics of bipedal locomotion, resulting in the risk of cephalopelvic
disproportion and injury (Washburn, 1960). Cephalopelvic disproportion occurs when the fetal head is too big, the maternal pelvis is too small, or when the fetal
head is malpositioned when it enters the birth canal (Maharaj, 2010). The ‘dilemma’ in the obstetrical dilemma refers to an increased risk of maternal and infant injury or mortality during childbirth because of this tight fit (Wittman and Wall, 2007; Wells et al., 2012; Kurki, 2013a). In modern contexts where biomedical services are available, these complications may lead to increased medical intervention during
childbirth, for example the use of forceps or vacuum extraction. When interventions such as these cannot allow for a safe delivery, birthing complications may lead to surgical procedures such as an emergency caesarean section (Wittman and Wall, 2007).
Currently, researchers are challenging the premise of the obstetrical dilemma from several directions, particularly how it is defined by Washburn (1960), by considering the effects ecological factors have on the growth of the bony pelvis, thus constricting maternal pelvic dimensions (Wells et al., 2012; Wells, 2015, Stone, 2016; Wells, 2017). Genetics and the environment both act on the human skeleton to determine body size and shape, and therefore variation is seen across as well as within human populations (Ruff, 1994; 2002; Duren et al., 2013). Poor nutrition related to unvaried, insufficient, poor quality diets of some agricultural populations may result in poor skeletal growth and therefore decreased pelvic size and
compromised shape, resulting in obstetric complications including obstructed labour (Wells et al., 2012). These increased risks across populations may be
identified in the archaeological record by observing disproportionately higher rates of death in young females (Hogberg et al., 1987; Pfieffer et al., 2014) who, as a result of compromised growth, may also have smaller pelvic canals and may have died in
childbirth. Through examining variation in female pelvic capacity in relation to age at death in a specific ecological context, such as an agricultural population, we can begin to build an understanding of variation in obstetric risk associated with certain ecological factors.
The aim of this thesis is to examine if childbirth may have been a significant mortality factor among young females in an agricultural population, specifically a medieval English population, and whether this potential mortality factor is associated with a smaller pelvic canal. More precisely, this thesis is directed at understanding the extent that environmental factors affect skeletal morphology of the human pelvis via biological plasticity, in turn potentially affecting the birthing process in human females. This will add to what is known about variation in pelvic shape and size across different human populations. With this knowledge, the data collected in this research contributes to understandings of the differences in the risk of birthing complications across different populations. This research also adds to the understanding of the lived experiences of women in middle to late medieval London by examining health and mortality.
1.2 Evolution and the Human Childbirth Process
Humans are the only obligatory bipedal primate, with significant changes to our pelvic morphology occurring during the course of hominin evolution. Human female pelvic canals are generally wider than male pelvic canals in order to accommodate for childbirth (Rosenberg and Trevathan, 2002; Wells et al., 2012).
Huseynov et al. (2016) propose that female pelvic morphology is reflective of obstetric rather than locomotor efficiency requirements in their analysis of pelvic
morphology change over the female life course; however, in experimental studies on hip abductor mechanics in men and women, Warrener et al. (2015) show that pelvic width does not correlate with locomotor efficiency. Over the course of hominin evolution, the ilium shifted forward and became broader, while the ischium became smaller in size. Moreover, the sacrum descended down to form a back to the pelvic
canal. These changes resulted in an increasingly constricted pelvic canal, relative to that of other primates, which has been argued to be better suited for bipedal
locomotion (Wittman and Wall, 2007).
While Homo was developing the pelvis for bipedal locomotion, larger brains
that required larger crania were also evolving (Wittman and Wall, 2007). Fischer and Mitteroecker (2015) have claimed that, as a result of strong correlational selection, females (and, although less pronounced, males) with large heads have pelvic canals shaped to accommodate neonates with large heads, and short females have rounder pelvic inlets, which may help to alleviate the obstetrical dilemma.
However, Underdown and Oppenheimer (2016) argue that, evolutionarily, there is a strong stabilizing pressure on maintaining an appropriate brain size to body size balanced against selective pressure for large brains. DeSilva’s (2010) research on infant mass relative to maternal mass in hominins demonstrates that large neonates had begun to develop rather early in human evolution, but the process of
encephalization that accompanied bipedalism was very slow during the early and
middle Pleistocene (approximately 1.8-‐0.6 million years ago). It has been argued that larger neonatal brains require human infants to be born earlier in order for the fetal cranium to pass through the birth canal, resulting in infant brains being
underdeveloped at birth (Washburn, 1960). As opposed to non-‐human primates, who have brains at birth measuring to 45-‐50% of adult size, humans give birth to infants with brains only approximately 25% of adult size (Trevathan, 2011). An alternative explanation for the early birth of human newborns is that limits to maternal metabolism primarily constrain human gestation lengths and fetal
development, resulting in an early timing of birth (Dunsworth et al., 2012;
Dunsworth and Eccleston, 2015; Dunsworth, 2018). Regardless, the altricial state of human newborns requires a long post-‐natal duration of nursing and childrearing from mothers (Rosenberg and Trevathan, 2002; Dunsworth et al., 2012).
Modern humans give birth differently than their closest primate relatives as a result of the constraints imposed by bipedal locomotion, large neonatal brains, and the altricial state of human newborns (Rosenberg and Trevathan, 2002; Trevathan, 2011). These evolutionary changes in Homo are argued to have resulted in frequent birthing complications among modern humans and birthing processes that require
assistance from others (Rosenberg and Trevathan, 2002). Unlike other primates that have neonatal head sizes more closely matching the dimensions of the mother’s birth canal, large human neonates must rotate in the birth canal due to their size and the shape of the maternal birth canal at different levels (the inlet, midplane, and outlet) (Rosenberg, 1992; Rosenberg and Trevathan, 2002; Walrath, 2003). Modern humans are not the only primates to have difficulty in childbirth – several other
primates also exhibit a narrow fit between the fetal head and maternal pelvis, however the extremely narrow fit and complex shape of the human birth canal results in a particularly increased risk of cephalopelvic disproportion (see Figure
1.1; Rosenberg and Trevathan, 2002). The evolution of fetal rotation in hominin species that precede anatomically modern humans is not well understood as the observable fossil record is limited and most specimens are damaged and incomplete (Dunsworth and Eccleston, 2015).
Figure 1.1. The relationship between the size of a human neonatal cranium and the maternal pelvic inlet (bottom right) compared to other primate species (Source: Rosenberg and Trevathan, 2002:1200).
The most common position at the start of human childbirth involves
alignment of the anterior-‐posterior axis of the neonate parallel to the long axis of the mother’s birth canal, with the neonate’s head positioned over the maternal pelvic inlet (Rosenberg, 1992). During birth, the body of the neonate rotates to align the neonate’s head, then shoulders, at the longest dimensions of the pelvic inlet, midplane, and outlet during childbirth (see Figure 1.2). The inlet is the entrance to the pelvic canal, lying at the level of the linea terminalis and sacral promontory and
tends to be longest in the medio-‐lateral dimension (Platzer, 2004; Kolesova and Vetra, 2011). The midplane lies at the level of the ischial spines, bounded by the lower pubic symphysis and the bodies of the fourth to fifth sacral vertebrae and is longest in the anterior-‐posterior dimension (Platzer, 2004). The outlet lies at the level of the ischial tuberosities bounded by the lower pubic symphysis and the base
of the fifth sacral vertebrae, and tends to be more circular in shape (Kolesova and Vetra, 2011) (see Figure 1.3). The changes in the dimension of greatest length among the pelvic canal planes mean the neonate must rotate to fit through the canal at each plane. Since the head and shoulders are the widest parts of the neonatal body, expulsion of the head and shoulders is most arduous in comparison to the rest of the body, which is typically born fairly quickly (Rosenberg, 1992).
Figure 1.2. Comparison of the birth mechanisms of Chimpanzees (left), Australopithecus (middle), and modern humans (right). Note the rotational birth mechanism in humans (Source: Rosenberg and Trevathan, 2002:1204).
Figure 1.3. The pelvic inlet, midplane, and outlet. The first image, ‘a,’ illustrates the pelvic inlet from a superior view, while from a posterior view, ‘b’ illustrates the midplane and ‘c’ illustrates the outlet. [Source: adapted from Kurki, 2013b:797].
Other primates generally birth their neonates facing the same direction as
the mother, allowing for the mother to reach down and guide the baby out of the birth canal, but human neonates are born facing posteriorly and therefore the mother cannot easily guide the baby (Rosenberg, 1992). This results in an increased risk of pulling the body of the neonate and damaging the spinal cord or other
muscles (Rosenberg, 1992; Rosenberg and Trevathan, 2002). Humans have adapted
to seek assistance during childbirth, generally resulting in human birth as a social rather than a solitary event, and reducing the risk of maternal and neonatal
mortality (Rosenberg, 1992; Rosenberg and Trevathan, 2002; Stone, 2016). In modern clinical biomedical childbirth settings, it is standard for women to birth in a supine position (laying flat on her back) or in the lithotomy position (on her back with her feet in stirrups) so that the attending practitioner can see and monitor the birth process; this differs from the upright birthing positions most commonly practiced prior to shifting childbirth into clinical spaces (Stone, 2016).
All of these characteristics create the unique and complex birthing process experienced by human females. However, some researchers have proposed that the obstetrical dilemma is not just the result of evolutionary change, but is also
determined by the environments in which humans live (Wells et al., 2012; Wells, 2015; Wells, 2017). This proposition has surfaced in the recognition of variation in rates of obstructed labour across populations and the acknowledgement that not all human populations live in the same environmental context. Varying ecological and cultural contexts (i.e. diet, disease load, activity, and climate, among others) may
underlie historical processes that have shaped the risk of obstructed labour in the face of compromised skeletal growth (Wells et al., 2012).
1.3 The Environment and Obstetric Risk
Wells et al. (2012) have argued that the quality of nutrition and overall health conditions may have an effect on skeletal growth and the dimensions of the human pelvis, leading to increased or decreased risks in obstructed labour among
females. Genetics play a role in human morphology as well, as bodies vary across different geographic regions. Ruff (1994, 2002) and Duren et al. (2013) have
commented on skeletal phenotypic variation across human populations. Ruff (2002) states that the most important influences on body size and shape historically are related to environmental factors such as climate, while nutritional factors may account for recent secular trends and variation in modern humans, resulting in differences in body shape and size among humans. Duren et al. (2013:49) note that
skeletal form is not determined solely by genetics or environment, but is rather represented by “environmental adaptations that play against a backdrop of genetic constraints.”
This interaction between biological plasticity, “the ability for an organism to
adapt during growth to stimuli” (Kurki 2013b:795), and genetic constraints is what gives rise to phenotypic variability (Duren et al., 2013). Kurki (2013b) suggests that the pelvic canal is highly plastic in comparison to other areas of the skeleton.
Sharma’s (2002) study on the role of genetic and environmental factors on pelvic morphology in an urban middle-‐class Punjabi population, which looked at 60 sets of
female twins, supports Kurki’s (2013b) conclusion, revealing a greater
environmental than genetic influence for the majority of the pelvic traits examined as pelvic size varied between twin pairs.
The prevalence of obstructed labour varies globally across different geographical regions and populations (Wells, 2017). According to Wells et al.
(2012), the obstetrical dilemma may be decreased or alternatively exacerbated in humans depending upon dietary availability and ecological factors. Further, the obstetrical dilemma may be affected by the speed of change in ecological factors
such as diet, with maternal size changing in one generation as a result of plasticity during growth and neonatal size being reduced over generations in response to ecological change (Wells, 2015). Wells et al. (2012) suggest that at the onset of agricultural practice, populations had an increased risk of obstructed labour due to the lack of nutritional availability, which would have affected their growth. For
instance, Wells et al. (2012) note that there is a connection between a reduction in skeletal stature and body size with a reduced pelvic canal size. However, as Wells et al. (2012) recognize and as Kurki (2013a) has illustrated, not all small bodied-‐ women have small pelves.
Kurki (2007; 2013a) showed that a population of Later Stone Age South African women with short stature did not necessarily exhibit small pelves, but exhibited pelves that were long anterior-‐posteriorly, and demonstrated variation among small-‐bodied populations in pelvic shape and pelvic capacity. Tague (2000) also noted that stature does not always correlate with body size, concluding that the
degree of correlation between height and pelvic size in females is low. With this in mind, Kurki (2013b) suggests that the size and shape of the pelvic canal are highly variable, indicating that the canal is highly plastic. Kurki and Decrausaz (2016) also suggest that pelvic canal shape is highly plastic in their discussion on canal shape variation compared to non-‐canal aspects of the limbs and pelvis within various populations.
Further, Wells et al. (2012) recognize that fetal size has a slow response to cultural changes, such as shifts to agricultural diets. Fetal size changes slowly across
generations (Jasienska, 2009; Wells, 2015), with fetal growth typically following maternal phenotype in a “one-‐generation time-‐lag” (Wells, 2015:8); fetal size can remain large relative to maternal pelvic size despite potential maternal pelvic size decreases due to poor maternal growth (Wells et al., 2012). Wells et al.’s (2012) criticism of the generic description of the obstetrical dilemma illustrates their
acknowledgement that both maternal pelvic dimensions and growth patterns of the fetus are sensitive to ecological factors such as nutritional intake as dictated by varying environmental contexts.
Wells et al. (2012) conclude that a reduced stature as a result of growth
disruptions from poor nutrition, resulting in small size among females, is arguably connected with small pelvic size and the possibility of increased obstetric risk. Support for this claim can be seen in a cross-‐examination of research on iron deficiency anemia by Rush (2000), who demonstrated that the low iron intake and absorption of severely anemic pregnant women is associated with shorter stature
and smaller size, and therefore an increased risk of maternal mortality. Further, in a biocultural examination of maternal mortality and reproductive risk management, Stone (2016) showed that female inequality as a result of poverty, lack of education, and inadequate nutrition effects rates of maternal mortality across the globe.
Therefore, as predicated by Wells et al. (2012), researchers should expect to see variation in the amount of obstetric risk across populations living under different
ecological conditions, as both maternal pelvic dimensions and the patterns of fetal growth are sensitive to ecological factors.
1.4 Cephalopelvic Disproportion
If Wells et al. (2012) are correct in predicting that ecological factors can affect the risk of obstetric complications such as cephalopelvic disproportion, then the rates of cephalopelvic disproportion must also vary across populations. In low-‐ income countries, obstructed labour is a large cause of maternal mortality (Wells, 2017). Cephalopelvic disproportion is known to currently be the most frequent
cause of obstructed labour (Dolea and AbouZhar, 2003). In the 2004 Global Burden of Disease Report issued by the World Health Organization (WHO), Mathers et al. (2008) outline the incidence of complications in pregnancy (among other selected conditions) in different regions of the world (Table 1.1). The incidence rate of obstructed labour across the world in 2008 was reported to be 4 million cases
(Mathers et al., 2008:28), but this number is distributed unevenly across the regions listed. For example, in the Americas, the incidence of obstructed labour per year is 100 000, while in South-‐East Asia, it is 1.9 million births per year (Mathers et al., 2008:28); however, it should be noted that population sizes may account for some of this difference. Although the regions listed encompass large and varied
populations, with individuals coming from diverse socioeconomic backgrounds where pregnancy complications disproportionately affect lower income groups, the statistics from this Global Burden of Disease Report illustrate that there are
variations in birth complications across populations.
Table 1.1. Incidence of selected conditions (per million) related to pregnancy and/or birth among women in various regions of the world as reported by the WHO in 2004 (adapted from Mathers et al., 2008:28). An entry of 0.0 in the table refers to an incidence of less than 50 000.
Complications of Pregnancy Wo rl d Af ri ca Th e Am er ic as Eas te rn Me d it er ra n ea n Eu ro p e So u th eas t A si a We st er n P ac if ic Maternal hemorrhage 12.0 3.0 1.2 1.6 0.7 4.0 1.4 Maternal sepsis 5.2 1.2 0.6 0.7 0.3 1.7 0.6 Hypertensive disorders 8.4 2.1 0.8 1.2 0.5 2.8 1.1 Obstructed labour 4.0 1.1 0.1 0.5 0.0 1.9 0.4 Unsafe abortion 20.4 4.8 4.0 2.9 0.5 7.4 0.8
Neilson et al. (2003), in their discussion on uterine contractions and the
muscular components of the pelvis in relation to obstructed labour, recognize that maternal height and the development of the bony pelvis is reflective of the
nutritional status of females in childhood, and suggest that in communities where childhood malnutrition is common, poor nutrition is linked with smaller pelves in females and higher rates of obstructed labour causing maternal death. Typically in
these nutrient-‐poor contexts, little medical intervention is available. In order to curb this problem, they suggest adequate nutrition will need to be provided universally from childhood in order to ensure proper growth into adulthood, though this is not an easy solution in parts of the world where sufficient quantities of high nutrient foods are unavailable (Neilson et al., 2003).
in low and middle-‐income countries as the “dual burden of malnutrition,” where short maternal stature is associated with poverty, malnutrition, female inequality, and therefore difficult delivery, and maternal obesity may result in difficult
childbirth due to fetal macrosomia (oversized offspring). Macrosomic offspring can also result from diabetes, which sometimes results from poor maternal nutrition
(Dolea and AbouZahr, 2003). The risk of short stature and obesity in women
overlaps, potentially due to the higher burden of malnutrition and infectious disease during growth in childhood resulting in stunting and increased food intake post-‐ childhood growth resulting in excess weight gain (Wells, 2017). Wells (2017:716) states “the association between the dual burden of malnutrition and the obstetrical dilemma is therefore expected to increase [in contemporary populations], because the obesity epidemic is emerging faster than stunting is being resolved.”
Kurki (2011) examined pelvic canal size as evidence of poor growth through examining populations of varying body sizes and shapes and looking at patterns of pelvic contraction. She illustrated that small-‐bodied individuals have higher incidences of contracted inlet and midplane posterior spaces of the pelvis. If we assume that clinical standards are valid and applicable to all populations, then we must also assume that the small-‐bodied women that are the subject of Kurki’s (2011) study are small because of constricted growth; Kurki (2011) argues that these small-‐bodied women exhibit normal growth patterns and that modern clinical standards fail to acknowledge varying human body size and shape as well as the effect human variation has on obstetric capacity and function (Kurki, 2011:147). Kurki (2011) concludes that the size and shape of the pelvis alone are not reliable
indicators of poor growth resulting from stress or risk in childbirth, though changes in a population over time could still be useful in understanding compromised
growth as a result of health or nutritional stress. With this in mind, it is argued that we would expect to see more young women comparative to young men in the skeletal record (Pfeiffer et al., 2014), as cephalopelvic disproportion may have been a cause of mortality for young women. Pfeiffer et al. (2014:15), using a sample of 119 male and 127 female late adolescent to young adult Later Stone Age South African foragers, showed that the ratio of young males to females may be used to examine obstetric death as a possible cause for mortality in past populations, as they found the risk of death to be twice as high for young females (2014:21).
Diets that are nutrient-‐deficient, including low protein and high-‐cereal diets, and diets that are less diverse can have a large impact on the skeleton through growth retardation in both the cranial and post-‐cranial skeleton (Sardi and Beguelin, 2011; Wells, 2015). This is particularly seen in populations that have
transitioned to agriculture (Stock and Pinhasi, 2011; Wells, 2015) as agricultural diets are high in carbohydrates and are associated with increases in the prevalence of infectious diseases associated with sedentary living (Wells, 2017). The
archaeological record reveals a higher rate of perinatal mortality in early
agricultural populations than in Holocene foragers, possibly indicating an increased risk of an obstetrical dilemma (Wells et al., 2012; Wells, 2015) and postnatal
infections. Given the impact that the adoption of agriculture had on human health, nutrition, and skeletal growth (LaVelle, 1995; Sardi and Beguelin, 2011; Stock and Pinhasi, 2011; Wells et al., 2012) this thesis will examine a medieval English sample
to determine whether long-‐term nutrient-‐poor agricultural diets led to poor skeletal growth and an increased risk of maternal death.
1.5 Nutrition, the Skeleton, and Population Demographics
Many researchers have provided evidence for variation in stature and body mass associated with agricultural subsistence across populations, though the direction of change is not always the same. While Auerbach (2011) noted an increase in body size in both male and female Indigenous southeastern North Americans during periods of agricultural intensification, other researchers have documented a decline in stature and body mass among populations who have adopted agriculture (Cohen and Armelagos, 1984; Larsen, 1995; Temple, 2008; Mummert et al., 2011; Stock and Macintosh, 2016). Cohen and Armelagos (1984) observed that of 21 societies that had undergone a transition to agriculture, 19 societies experienced a declining trend in health, resulting from nutritional disease from seasonal hunger, crop blights, social inequalities, and a reliance on single crops that are deficient in nutritional value. In their review of a number of studies that assess the impact of agriculture on populations, Mummert et al. (2011) support these findings, noting that agriculture increases population density and the spread of infectious disease, and find that many studies cite agriculture as associated with a decrease in stature in populations all across the world. One of these studies showed a significant decrease in stature for both males and females from western Japan in the Late/Final Period (4000-‐2500 BP) (approximately 4 cm for males and 2.5 cm for females), which is associated with an increase in infectious diseases and
