Chapter

Evolution and Endocrinology The Regulation of Pregnancy Outcomes

Authors:
To read the full-text of this research, you can request a copy directly from the author.

Abstract

Introduction Some time this past year, the earth’s human population rose past 6.5 billion living persons. Roughly 130 million babies were born in 2006, which translates into about 350,000 per day. Impressive as these gures are, they represent but a fraction of an invisible industry. For every human birth, as many as four conceptions never reached fruition-nearly 1.4 million each and every day, and more than half a billion lost human conceptions each year. Having breathed a sigh of relief on behalf of the planet that such potential was not realised, one is left to wonder at the extraordinary inefciency of this biological economy. Why hasn’t natural selection during 6 million years of human evolution honed a sleeker assembly line?.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the author.

... Consistent with what is now known of the normally hypoxic early intrauterine environment, the rate of early pregnancy loss (EPL) in hormonally detected conceptions in rural Aymara women was comparable with that in a study of (low altitude) North Carolina women (Vitzthum, 2008a;Vitzthum et al., 2006Vitzthum et al., , 2009aWilcox et al., 1988). Furthermore, contrary to the widespread belief that EPL are almost wholly the outcome of genetic abnormalities, the rate of EPL varied significantly with the agricultural cycle in these altiplano communities (Fig. 2). ...
... The rate of loss of pregnancies detected and reported by a woman ranged from 7% to 17% in eight developing countries' surveys (Casterline, 1989). Estimates for industrialized populations at sea level vary from 10% to 15% (Vitzthum, 2008a). Rates reported for the Himalaya are: 10% among Nepalese Sherpas (Lang and Lang, 1971) and Tibetans living at 3,000 to 4,000 m (Moore et al., 2001); 6% in Zangskar, Ladakh (Elford, 1994); 9% in a more urban Ladakh sample (Wiley, 2003); and 3.4% in Jumla, Nepal (Geetha et al., 1995). ...
... However, the estimate from the only prospective study at high altitude to use hormonal indicators (Project REPA) is based on a small sample and hence has a wide confidence interval (0%-24%). The other estimates are based on clinical records and/or women's recall, which typically underestimate the true rate of loss (Chen and Murray, 1976;Vitzthum, 2008a). An adequate study of later pregnancy loss probably requires a longitudinal design incorporating socioeconomic and energetic indicators along with hormonal biomarkers. ...
Article
Early European colonists of the Andes had difficulties in reproducing, a fact that underpins the hypothesis that reproduction is impaired amongst all humans at high altitudes. Yet a 16th century missionary wrote, "... the Indians are healthiest and where they multiply the most prolifically is in these same cold air-tempers, ... [yet most children of the Spaniards] when born in such regions do not survive." These observations suggest that humans at high altitudes are subjected to strong natural selection from hypoxia, cold and limited food sources and, furthermore, that human populations can and have adapted, and continue to adapt, to these conditions. Informed by multiple approaches and theoretical frameworks, anthropologists have investigated to what extent and precisely how high altitude environments impact human reproductive functioning and fertility. Analyses of the proximate determinants of natural fertility suggest that behaviors (breast/infant feeding practices in the Andes, and marriage practices and religious celibacy in the Himalaya) are major determinants of fertility in high altitude populations. Furthermore, data from Project REPA (Reproduction and Ecology in Provincía Aroma), a longitudinal study in rural Bolivia, demonstrate that fecundity is not impaired in this indigenous altiplano population, and that the risk for early pregnancy loss (EPL) is not elevated by environmental hypoxia but does vary seasonally with the agricultural cycle (contra to the assumption that EPLs are due almost entirely to genetically flawed concepti). This review discusses these and other findings that reveal the complex and dynamic adaptations of human reproductive functioning in high altitude environments. Am. J. Hum. Biol. 25:179-189, 2013.
... In 1976, ''The Evolution of Human Reproduction'' by physiologist Roger Short squarely placed human fertility patterns within an evolutionary framework. Since then, bioanthropologists and human biologists have contributed to a rapidly growing body of evidence on the extent and causes of natural (nonpathological) variation in human reproductive functioning (e.g., Bribiescas, HARRISAND VITZTHUM 2001;Ellison, Peacock, & Lager, 1989;Holman, 1996;Konner & Worthman, 1980;Leslie & Fry, 1989;Nepomnaschy, Welch, McConnell, Strassmann, & England, 2004;Strassmann, 1997;Vitzthum, 1989Vitzthum, , 2008aVitzthum, Worthman, et al., 2009;Wood, Johnson, & Campbell, 1985). Concurrently, and somewhat independently, other anthropologists have focused on the application of ''evolutionary ecology models and concepts to the study of human behavioral diversity'' (Winterhalder & Smith, 2000, p. 51), including modeling and measuring variation in reproductive behavior (i.e., mating strategies and parental investment) and associated outcomes (e.g., reproductive success). ...
... Dropping hormone levels eventually prompt endometrial shedding (menses), denoting the beginning of the next cycle. HARRIS AND VITZTHUM about one week after implantation (Vitzthum, 2008a). Apparent fecundability is an approximation estimated from the conceptions that are detected (Wood, 1994). ...
... Second, most studies have primarily recruited Caucasian women who are at least middle class and can afford health care; many studies have recruited from physicians' or counselors' offices. Women in different cultures likely have different perceptions of menopause, and it is also now well established that women with different sociocultural backgrounds and=or lifestyles can have dramatically different natural hormone levels (Briggs & Briggs, 1972;Haiman et al., 2002;Key et al., 1990;Vitzthum, 2008aVitzthum, , 2008bVitzthum, , 2009Vitzthum et al., 2002;Windham et al., 2002). It stands to reason that this hormonal variation would continue through the menopausal transition. ...
Article
Full-text available
On the Origin of Species, published just over 150 years ago, has deeply influenced thinking in both scientific and wider communities. Darwin's legacy includes recognition of the fact that all organisms evolve; that variation within and between species is natural and normal; and that an evolutionary approach to understanding the sources and consequences of this variation comprises theoretical frameworks, testable hypotheses, and rigorously collected evidence. With an eye toward facilitating communication and productive collaboration among researchers from different intellectual traditions who nonetheless share a common interest in women's reproductive and sexual functioning, we discuss evolutionary concepts and models, summarize the known variability in ovarian functioning and consider the implications of this variability for conducting sex research, and evaluate the relative merits of various biomarkers that serve as proxy measurements of a woman's reproductive and hormonal status. With these perspectives and methods from reproductive ecology at hand, we examine several contentious issues: the links between hormones and sexuality in premenopausal and perimenopausal women, the causes of premenstrual syndrome, and the existence (or not) of menstrual synchrony. In none of these cases is as much known as is often claimed. In each, there are abundant opportunities for innovative, albeit challenging, research.
... Consistent with what is now known of the normally hypoxic early intrauterine environment, the rate of early pregnancy loss (EPL) in hormonally detected conceptions in rural Aymara women was comparable with that in a study of (low altitude) North Carolina women (Vitzthum, 2008a;Vitzthum et al., 2006Vitzthum et al., , 2009aWilcox et al., 1988). Furthermore, contrary to the widespread belief that EPL are almost wholly the outcome of genetic abnormalities, the rate of EPL varied significantly with the agricultural cycle in these altiplano communities (Fig. 2). ...
... The rate of loss of pregnancies detected and reported by a woman ranged from 7% to 17% in eight developing countries' surveys (Casterline, 1989). Estimates for industrialized populations at sea level vary from 10% to 15% (Vitzthum, 2008a). Rates reported for the Himalaya are: 10% among Nepalese Sherpas (Lang and Lang, 1971) and Tibetans living at 3,000 to 4,000 m (Moore et al., 2001); 6% in Zangskar, Ladakh (Elford, 1994); 9% in a more urban Ladakh sample (Wiley, 2003); and 3.4% in Jumla, Nepal (Geetha et al., 1995). ...
... However, the estimate from the only prospective study at high altitude to use hormonal indicators (Project REPA) is based on a small sample and hence has a wide confidence interval (0%-24%). The other estimates are based on clinical records and/or women's recall, which typically underestimate the true rate of loss (Chen and Murray, 1976;Vitzthum, 2008a). An adequate study of later pregnancy loss probably requires a longitudinal design incorporating socioeconomic and energetic indicators along with hormonal biomarkers. ...
Article
Early European colonists of the Andes had difficulties in reproducing, a fact that underpins the hypothesis that reproduction is impaired amongst all humans at high altitudes. Yet a 16th century missionary wrote, "… the Indians are healthiest and where they multiply the most prolifically is in these same cold air-tempers, … [yet most children of the Spaniards] when born in such regions do not survive." These observations suggest that humans at high altitudes are subjected to strong natural selection from hypoxia, cold and limited food sources and, furthermore, that human populations can and have adapted, and continue to adapt, to these conditions. Informed by multiple approaches and theoretical frameworks, anthropologists have investigated to what extent and precisely how high altitude environments impact human reproductive functioning and fertility. Analyses of the proximate determinants of natural fertility suggest that behaviors (breast/infant feeding practices in the Andes, and marriage practices and religious celibacy in the Himalaya) are major determinants of fertility in high altitude populations. Furthermore, data from Project REPA (Reproduction and Ecology in Provincía Aroma), a longitudinal study in rural Bolivia, demonstrate that fecundity is not impaired in this indigenous altiplano population, and that the risk for early pregnancy loss (EPL) is not elevated by environmental hypoxia but does vary seasonally with the agricultural cycle (contra to the assumption that EPLs are due almost entirely to genetically flawed concepti). This review discusses these and other findings that reveal the complex and dynamic adaptations of human reproductive functioning in high altitude environments. Am. J. Hum. Biol., 2013. © 2013 Wiley Periodicals, Inc.
... Because lactation can suppress the HPO axis (McNeilly, 2001), breastfeeding women are typically excluded from studies of ''normal'' ovarian cycling (although this selection bias may exclude women of higher fecundity). But because most pregnancies are lost shortly after conception (Vitzthum, 2008a), it is much more difficult to exclude segments from pregnant women who are unaware of having conceived. Assuming a modest fecundability of 0.20 and a modest risk of early pregnancy loss (EPL) of 50%, 100 non-contracepting study participants would have 20 conceptions/month of which half (10% of the sample) would be lost without detection. ...
... The modulation of reproductive effort in humans extends, of course, beyond conception. Ovarian functioning continues to play a critical role in adjusting these investments, including those necessary for the maintenance of early pregnancy ( Csapo et al., 1972;Sunder and Lenton, 2000;Norwitz et al., 2001;Baird et al., 2003;Vitzthum, 2008a). In fact, a prospective study of nearly 500 Bangladeshi women observed little decline in fecundity with age but dramatic increases in EPL (Holman, 1996;Holman et al., 2000;Holman and Wood, 2001). ...
... These findings suggest that the role of the HPOaxis in regulating reproductive effort may be as important after fertilization as before. The few weeks following conception and implantation present a low cost opportunity to curtail investment if maternal evaluation of offspring quality and available resources find either to be inadequate (Haig, 1990(Haig, , 1993(Haig, , 1999Stearns, 1987;Nepomnaschy et al., 2006;Vitzthum, 2008a). The approximately two-fold seasonal variations of EPL risk in Bolivian (see Fig. 12) (Vitzthum et al., 2009a) and North Carolinian women (Weinberg et al., 1994) support this hypothesis: seasonal variation would not be expected if EPL were overwhelmingly attributable to genetic defects of the conceptus (as had been hypothesized by Bishop, 1964). ...
Article
Human reproductive ecology (HRE) is the study of the mechanisms that link variation in reproductive traits with variation in local habitats. Empirical and theoretical contributions from biological anthropology, physiology, and demography have established the foundation necessary for developing a comprehensive understanding, grounded in life history theory (LHT), of temporal, individual, and populational variation in women's reproductive functioning. LHT posits that natural selection leads to the evolution of mechanisms that tend to allocate resources to the competing demands of growth, reproduction, and survival such that fitness is locally maximized. (That is, among alternative allocation patterns exhibited in a population, those having the highest inclusive fitness will become more common over generational time.) Hence, strategic modulation of reproductive effort is potentially adaptive because investment in a new conception may risk one's own survival, future reproductive opportunities, and/or current offspring survival. The hypothalamic-pituitary-ovarian (HPO) axis is the principal neuroendocrine pathway by which the human female modulates reproductive functioning according to the changing conditions in her habitat. Adjustments of reproductive investment in a potential conception are manifested in temporal and individual variation in ovarian cycle length, ovulation, hormone levels, and the probability of conception. Understanding the extent and causes of adaptive and non-adaptive variation in ovarian functioning is fundamental to ascertaining the proximate and remote determinants of human reproductive patterns. In this review I consider what is known and what still needs to be learned of the ecology of women's reproductive biology, beginning with a discussion of the principal explanatory frameworks in HRE and the biometry of ovarian functioning. Turning next to empirical studies, it is evident that marked variation between cycles, women, and populations is the norm rather than an aberration. Other than woman's age, the determinants of these differences are not well characterized, although developmental conditions, dietary practices, genetic variation, and epigenetic mechanisms have all been hypothesized to play some role. It is also evident that the reproductive functioning of women born and living in arduous conditions is not analogous to that of athletes, dieters, or even the lower end of the "normal range" of HPO functioning in wealthier populations. Contrary to the presumption that humans have low fecundity and an inefficient reproductive system, both theory and present evidence suggest that we may actually have very high fecundity and a reproductive system that has evolved to be flexible, ruthlessly efficient and, most importantly, strategic.
... Early pregnancy loss (EPL) is the most common, yet least understood, fate of a human conception. The rate of EPL (usually defined as terminations occurring prior to 6 weeks gestation) may be as high as 80% of all fertilized ova (Holman and Wood, 2001;Roberts and Lowe, 1975) yet despite its frequency, the causes of EPL are uncertain (Macklon et al., 2002;Regan and Rai, 2000;Vitzthum, 2008a). Life history theory may be able to explain a large measure of this apparent inefficiency of the human reproductive system. ...
... Thus, many authors have argued that short-term perturbations in women's reproductive functioning (e.g., changes in hormone levels and/or failure to ovulate or failure to maintain a pregnancy) concomitant with energetic or other stressors could be adaptive responses to such challenges (Ellison, 1990(Ellison, , 1994(Ellison, , 2003Frisch and Revelle, 1970;Jasienska, 2001;Nepomnaschy et al., 2004Nepomnaschy et al., , 2006Peacock, 1990Peacock, , 1991Prior, 1985aPrior, ,b, 1987Vitzthum and Smith, 1989;Vitzthum, 1990Vitzthum, , 1997Vitzthum, , 2001Vitzthum, , 2008aWasser and Barash, 1983). Although this argument is consistent with evolutionary theory, it has yet to be empirically demonstrated in any human population that such responses to environmental conditions do, in fact, increase relative fitness. ...
... As demanding as it has been to demonstrate correlations between environmental challenges and indicators of ovarian functioning, it has proven even more difficult to address the question of whether EPL may be, at least in some instances, another adaptive mechanism. Because most conceptions are lost without having been detected in the first place (Holman and Wood, 2001;Vitzthum, 2008a), until recently it was impossible to ascertain whether there are any associations between the risk of EPL and the occurrence of some stressor. The development of sensitive assays for hCG (human chorionic gonadotrophin, produced by the conceptus) afforded the opportunity to detect a conception from about the time of implantation and to follow it through to loss or birth. ...
Article
Life history theory predicts that early pregnancy presents a relatively low cost, uncontested opportunity for a woman to terminate investment in a current reproductive opportunity if a conceptus is of poor quality and/or maternal status or environmental conditions are not propitious for a successful birth. We tested this hypothesis in rural Bolivian women experiencing substantial seasonal variation in workload and food resources. Significant risk factors for early pregnancy loss (EPL) included agropastoralism versus other economic strategies, conception during the most arduous seasons versus other seasons, and increasing maternal age. Anovulation rate (AR) was higher during the most arduous seasons and in older women. Breastfeeding and indicators of social status and living conditions did not significantly influence either risk of EPL or AR. Averaged over the year, anovulation occurred in about 1/4 of the cycles and EPL occurred in about 1/3 of the conceptions. This is the first evidence of seasonality of EPL in a non-industrialized population, and the first to demonstrate a relationship between economic activities and EPL. These findings suggest that both anovulation and EPL are potential mechanisms for modulating reproductive effort; such "failures" may also be nonadaptive consequences of conditions hostile to a successful pregnancy. In either case, variation in EPL risk associated with different subsistence activities can be expected to influence fertility levels and birth seasonality in both contemporary and past human populations. These consequences of variability in the risk of EPL can impact efforts to understand the sources of variation in reproductive success.
... In contrast, the parental strategy is to produce healthy offspring (that lives to reproduce) at the lowest possible cost. Vitzthum (Vitzthum, 2008) explains that it is in a human mother's best interest to balance resources among previous, current, and future offspring to ensure their survival to reproductive maturity. The highlevel, subconscious con ict is theorized to be ul timate ly due to sexual reproduction because a child's genes are 50% different than those of either parent. ...
... With his model, investment is evolutionarily "worthwhile" if rB > C. The prediction therefore is that animals, including humans, will preferentially invest in close relatives, individuals with perceived high potential for future reproduction, and those who incur relatively low costs (Strassman, 2008). Evolutionary theorists have framed aspects of women's reproductive experience previously regarded as pathological, such as nausea during pregnancy (Flaxman & Sherman, 2008;Profet, 1992) and miscarriage (Haig, 1993;Vitzthum, 2008) as energetically protective for the mother. Morning sickness is considered a defensive mechanism against maternal ingestion of teratogens that could harm the developing embryo, and early pregnancy loss can be a screening tool for conceptions that are not likely to survive long term. ...
Chapter
Full-text available
In this chapter, we use an evolutionary lens to deepen understanding of maternal and family needs in the early postpartum period so that health care can be more aligned with confronted realities. The discussion is centered around the concept of the 4th trimester, which is the period between birth and the first 3 months postpartum. This framework encourages a holistic understanding of perinatal health by drawing attention to evolved maternal-infant needs. By addressing these ultimate-level contributors to health issues, we can facilitate more effective clinical support, comprehensive research, and a fuller “village” to enable new families to thrive. Core to this approach is the concept of trade-offs between parents and offspring, exemplified by lactation as a prime example of the complexities of dyadic needs and gap between the current culture of health and optimal support.
Article
A detailed understanding of female reproductive functioning is important to many disciplines including anthropology, evolutionary theory, demography, psychology, and biomedicine. In this article, I describe strategies and methods that have been used successfully in community‐based studies of human reproduction, many in remote locales, to produce high quality biomarker data. These techniques are applicable to a wide range of research questions and populations, and to persons from adolescence through senescence. I give particular attention to the inherent challenges imposed by the cyclical and somewhat unpredictable nature of the hypothalamic‐pituitary‐ovarian axis including the necessity and difficulty of ascertaining the timing and occurrence of ovulation, the limits of different sampling regimes for capturing fluctuations in reproductive hormones, and the critical importance of recognizing and, when possible, reducing selection bias. I discuss the relative advantages and disadvantages of collecting saliva, urine, and dried blood spots, and describe some of the subtleties involved in collecting contamination‐free samples. Once samples are collected, they must be stored in a manner that minimizes degradation; I describe techniques to keep samples cold even without access to electricity or dry ice. I also discuss various issues that should be considered during initial discussions with a laboratory and when samples are assayed by the laboratory. I include examples of techniques that have worked well in actual field studies, and examples of flawed analytical approaches that should be avoided. With these and other tools, even under technology‐sparse conditions, researchers can investigate variability in human physiology across the breadth of human habitats.
ResearchGate has not been able to resolve any references for this publication.