Human Reproductive Ecology Research Articles

Phenotypic Signals of Sexual Selection and Fast Life History Dynamics for the Long-Term but Not Short-Term Mating.

Mating patterns are crucial for understanding selection regimes in current populations and highly implicative for sexual selection and life history theory. However, empirical data on the relations between mating and reproductive outcomes in contemporary humans are lacking. In the present research we examined the sexual selection on mating (with an emphasis on Bateman's third parameter - the association between mating and reproductive success) and life history dynamics of mating by examining the relations between mating patterns and a comprehensive set of variables which determine human reproductive ecology. We conducted two studies (Study 1: N = 398, Study 2: N = 996, the sample was representative for participants' sex, age, region, and settlement size). The findings from these studies were mutually congruent and complementary. In general, the data suggested that short-term mating was unrelated or even negatively related to reproductive success. Conversely, long-term mating was positively associated with reproductive success (number of children in Study 1; number of children and grandchildren in Study 2) and there were indices that the beneficial role of long-term mating is more pronounced in males, which is in accordance with Bateman's third principle. Observed age of first reproduction mediated the link between long-term mating and number of children but only in male participants (Study 2). There were no clear indications of the position of the mating patterns in human life history trajectories; however, the obtained data suggested that long-term mating has some characteristics of fast life history dynamics. Findings are implicative for sexual selection and life history theory in humans.

Reproductive hormone measurement from minimally invasive sample types: Methodological considerations and anthropological importance.

Energetic investment in human reproduction has long been recognized as costly, influencing developmental, physiological, and behavioral patterns in males and females. These effects are largely coordinated through the actions of reproductive hormones (eg, testosterone, estradiol, and progesterone). Here, the utility and limitations of minimally invasive sampling techniques are explored, providing a novel perspective on how reproductive hormone measurements can enhance reproductive endocrinology research. Salivary steroid measures are most commonly used, although several dried blood spot and urine assays are also available, and researchers continue to explore the efficacy of other sample types. These relatively simple measures have facilitated the collection of multiple samples from a single participant, allowing researchers to more accurately track the diurnal and cyclical variation exhibited by many reproductive hormones. Ultimately, the ability to collect fine-grained participant data allows biological anthropologists to better test questions central to human reproductive ecology, life history theory, and public health. For example, fieldwork using these techniques suggests that testosterone profile variation across populations is influenced by energetic constraints and reproductive status. Moreover, hormone concentrations shape the development of sex characteristics, with implications for evolutionary questions related to sexual selection. Hormone levels also can be used to identify a range of medical concerns (eg, suppressed hormone production levels linked with psychosocial stress). These findings highlight how minimally invasive collection techniques can be applied to test diverse evolutionary hypotheses and identify important health concerns. Still, more work is needed to standardize collection and laboratory analysis procedures, thereby enabling more direct data comparisons between researchers.

Body composition helps: Differences in energy expenditure between pregnant and nonpregnant females.

Human pregnancy is associated with important physiological changes that usually increase energetic requirements. However, great variability exists in the costs and mechanisms required to bear pregnancy. Since body mass (BM) and composition are modified during gestation, it is of great interest to compare the influence of BM on energy expenditure (EE) in pregnant and nonpregnant females. BM, body composition, and EE of 77 volunteers (35 pregnant and 42 nonpregnant females) were measured. The pregnant volunteers completed two measurement rounds at 28 and 32 gestation weeks. Differences on the measured parameters were sought, and comparison of regression lines was computed to test how BM affected the EE of the volunteers. BM and body composition parameters are significantly higher in pregnant females, but EE is not statistically different. Pregnant females have a larger percentage of fat mass, but lower percentage of fat-free mass (FFM). The EE per kg of FFM is similar in both groups. Comparison of regression lines shows that pregnancy does not change the relationship between BM and EE, but for similar BM pregnant females expend less energy than nonpregnant females. We propose that their larger percentage of passive body tissues is the reason why pregnant females expend less energy than nonpregnant females of similar BM, without changing the scaling of EE on BM. Thus, pregnancy could not be as energetically constraining as usually assumed, with important consequences for human reproductive ecology.

Age at menarche and parity are independently associated with Anti‐Müllerian hormone, a marker of ovarian reserve, in filipino young adult women

Despite ample evidence of variation in timing of menopause, little is known about the extent or underlying causes of individual variation in ovarian reserve and age-related follicular decline. Anti-Müllerian hormone (AMH), a hormonal marker of ovarian reserve, may be a useful tool to clarify these questions. We describe AMH in a cohort of Filipino young adult women, and evaluate whether ovarian reserve in early adulthood relates to measures of life history scheduling (menarcheal age) and reproductive effort (parity). Data and samples are obtained from 294 nonpregnant participants (21.5 years ± 0.3) in the Cebu Longitudinal Health and Nutrition Survey. Plasma AMH was assayed using an enzyme immunoassay and relationships between AMH, menarcheal age, and parity were examined. Mean AMH was 4.3 ng/mL. In multiple regression models, women who experienced menarche earlier had significantly higher AMH as young adults (P < 0.05). Women with two (P < 0.05) and three or more (P < 0.01) children had significantly lower AMH than those with no children. These associations were independent of age, smoking, and body mass index. These findings suggest that individual variation in life history scheduling and reproductive history could contribute to variation in ovarian reserve. Moreover, they demonstrate the utility of AMH as a tool for human reproductive ecology, and highlight the need for further research clarifying the extent of human population variation in ovarian reserve and the behavioral and ecological influences underlying this variation.

Evidence for evolution in response to natural selection in a contemporary human population

It is often claimed that modern humans have stopped evolving because cultural and technological advancements have annihilated natural selection. In contrast, recent studies show that selection can be strong in contemporary populations. However, detecting a response to selection is particularly challenging; previous evidence from wild animals has been criticized for both applying anticonservative statistical tests and failing to consider random genetic drift. Here we study life-history variation in an insular preindustrial French-Canadian population and apply a recently proposed conservative approach to testing microevolutionary responses to selection. As reported for other such societies, natural selection favored an earlier age at first reproduction (AFR) among women. AFR was also highly heritable and genetically correlated to fitness, predicting a microevolutionary change toward earlier reproduction. In agreement with this prediction, AFR declined from about 26-22 y over a 140-y period. Crucially, we uncovered a substantial change in the breeding values for this trait, indicating that the change in AFR largely occurred at the genetic level. Moreover, the genetic trend was higher than expected under the effect of random genetic drift alone. Our results show that microevolution can be detectable over relatively few generations in humans and underscore the need for studies of human demography and reproductive ecology to consider the role of evolutionary processes.

Book review: Reproduction and adaptation: Topics in human reproductive ecology

Book review: Reproduction and adaptation: Topics in human reproductive ecology

The ecology and evolutionary endocrinology of reproduction in the human female

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.

Grant Recipients

Anthropology NewsVolume 48, Issue 9 p. 32-32 Grant Recipients First published: 29 December 2008 https://doi.org/10.1525/an.2007.48.9.32AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract •Teaching Theories in Human Reproductive Ecology•Cave Arts of the Upper Karawari in Papua New Guinea Volume48, Issue9December 2007Pages 32-32 RelatedInformation

Constraint, pathology, and adaptation: How can we tell them apart?

Adaptation is a central concept of modern evolutionary biology, but remains a difficult one nevertheless. Definitions of adaptation are often confounded with definitions of natural selection, rendering them somewhat circular and difficult to operationalize. Williams introduced a definition that avoids such tautology and a strategy for testing adaptive claims against chance as an alternative explanation for design complexity. Gould and Lewontin ([1979]: Proc R Soc Lond B Biol Sci 205:581-598) challenged this strategy for pitting adaptation against a straw alternative, and argued that constraint is often the cause of design complexity. The field of Darwinian medicine has underscored the fact that adaptation can also be difficult to discriminate from pathology, which can also produce design complexity. We suggest that an updated version of Williams' strategy is to consider any claim of adaptation against constraint and pathology as alternatives. We use an example drawn from the intersection of human reproductive ecology and developmental biology to illustrate how this updated strategy can be applied. Where we can generate distinct predictions for the three alternative hypotheses, constraint, pathology, and adaptation, we have a better situation in which to evaluate adaptive claims with a real possibility of falsification. We view this strategy as an improvement over Williams' original suggestion, but not as a definitive strategy. Further advances, however, will likely also be based on a sound understanding of the concept of adaptation and the identification of the strongest competing alternatives to it.

Human Reproductive Ecology. A Question to Consider

Human Reproductive Ecology. A Question to Consider

Human Reproductive Ecology. An Issue to Observe

Human Reproductive Ecology. An Issue to Observe

Labor-saving technology and fertility increase in rural Africa.

Across the developing world, labor-saving technologies have been designed and implemented to introduce savings in the time and energy that women allocate to work. In rural Arsi, southern Ethiopia, a recent water-supply scheme has reduced long arduous trips to obtain water and is associated with considerable improvements in women’s energy budgets. Assuming that the time and energy saved is not diverted to other energetically costly activities and nutritional levels remain constant, evolutionary life-history theory predicts that this energy may be diverted into reproductive effort and thus may increase fertility. The aims of this bio-demographic study are to detect any effects of the installation of village water taps on birth spacing and women’s overall energetic status. Field studies in human reproductive ecology have revealed that fertility is responsive to changes in maternal condition (Hill and Hurtado 1996, Tracer 1991). Other clinical trials have identified the physiological pathways along which energetic factors influence reproductive function (Ellison 2001). A negative energy balance, attributed to the combined effect of seasonal high workloads and low nutritional reserves, is associated with reduced fecundity (Bailey et al. 1992, Ellison, Peacock, and Lager 1989, Panter-Brick, Lotstein, and Ellison 1993). Although the effects of short-term seasonal alteration in energy levels have been explored, the effect of long-term changes under conditions of poor nutrition is less well understood. The proposed study is the first to investigate whether physiological changes associated with workload affect fertility at a population level—that is, translate

Physical work causes suppression of ovarian function in women.

The suppression of reproductive function is known to occur in women engaging in activities that require high energetic expenses, such as sport participation and subsistence work. It is still unclear, however, if reproductive suppression is a response to high levels of energy expenditure, or only to the resulting state of negative energy balance. To our knowledge, this study provides the first evidence that work-related energy expenditure alone, without associated negative energy balance, can lead to the suppression of reproductive function in women. We document suppression of ovarian function expressed as lowered salivary progesterone levels in women from an agricultural community who work hard, but remain in neutral energy balance. We propose two alternative evolutionary explanations (the 'pre-emptive ovarian suppression' hypothesis and the 'constrained down-regulation' hypothesis) for the observed results.

Evolutionary ecology of human reproduction.

▪ Abstract Evolutionary ecology of human reproduction is defined as the application of natural selection theory to the study of human reproductive strategies and decision-making in an ecological context. The basic Darwinian assumption is that humans—like all other organisms—are designed to maximize their inclusive fitness within the ecological constraints to which they are exposed. Life history theory, which identifies trade-off problems in reproductive investment, and evolutionary physiology and psychology, which analyzes the adaptive mechanisms regulating reproduction, are two crucial tools of evolutionary reproductive ecology. Advanced empirical insights have been obtained mainly with respect to the ecology of fecundity, fertility, child-care strategies, and differential parental investment. Much less is known about the ecology of nepotism and the postgenerative life span. The following three theoretical aspects, which are not well understood, belong to the desiderata of future improvement in evolutionary human reproductive ecology: (a) the significance of and the interactions between different levels of adaptability (genetic, ontogenetic, and contextual) for the adaptive solution of reproductive problems; (b) the dialectics of constraints and adaptive choices in reproductive decisions; and (c) the dynamics of demographic change.

Book Review

Book reviewed in this article:Campbell KL, Wood JW. Human Reproductive Ecology— Interactions of Environment, Fertility, and Behavior. New York: New York Academy of Sciences, 1994.

Advances in human reproductive ecology.

Human reproductive ecology pertains to reproduction biology and changes due to environmental influences. The research literature relies on clinical, epidemiological, and demographic analysis. The emphasis is on normal, nonpathological states and a broad range of ecological conditions. This review focused on the importance of age and energetic stress from ecological conditions rather than dieting or self-directed exercise in changing female fecundity. The literature on male reproductive ecology is still small but growing. J.W. Wood provided a comprehensive overview of the field. Natural fertility, as defined by Henry, is the lack of parity-specific fertility limitation. There is evidence that fertility can vary widely in natural fertility populations. There are consistent age patterns among different natural fertility populations. Doring found that there was higher frequency of anovulatory and luteal insufficiency in cycles during perimenarche and perimenopausal periods. Infertility studies have shown declines in pregnancy rates in women over the age of 30 years. Ovum donation evaluations have found both uterine age and ovarian and oocyte age to be related to the probability of a successful pregnancy. Basal follicle stimulating hormone and the endometrial thickness are important predictors of ovarian capacity and related to age and declining fecundity. Much of the literature on fecundity is derived from women with impaired reproductive physiology. In Lipson and Ellison's study of healthy women, average follicular and average luteal estradiol values declined with increasing subject age. Low follicular levels were correlated with smaller follicular size, low oocyte fertilizability, reduced endometrial thickness, and low pregnancy rates. Comparisons across populations have shown that populations experience declines in luteal function with age, but levels of luteal functions varied widely. Chronic conditions which slow growth and delay reproductive maturation may impact on lower ovarian function throughout adult life. There is a range of ovarian function along a continuum due to energetic stress. Evidence from the Lese in Zaire, the Tamang of Nepal, and Polish farm women outside Crakow suggest that workload affects ovarian function. Luteal function and ovulatory frequency is lower when women are losing weight. Among the Tamang losing weight between seasons there was evidence of lower ovarian function during the monsoon season. Polish farm women who work very hard in summer had lower ovarian function. The effect of lactation on amenorrhea appears to be due to the energetic stress on the mother in the intensity and duration of suckling. Women in poorer nutritional status may require more intense suckling. Seasonality of energy balance may be related to seasonality of female fecundity and conceptions.

Human reproductive ecology: conference summary.

Human reproductive ecology: conference summary.

Funding considerations in human reproductive ecology: summary of an evening panel discussion on sources and resources.

Funding considerations in human reproductive ecology: summary of an evening panel discussion on sources and resources.

Introduction: what is human reproductive ecology, and why should we care about studying it?

Introduction: what is human reproductive ecology, and why should we care about studying it?

Comparative study of breastfeeding structure and its relation to human reproductive ecology

Although a controversial issue in the not distant past, it is now well established that breastfeeding is the primary factor mediating post-partum subfecundity. This complex interaction between behavior and physiology is a central research focus in several fields sharing a common concern with the mechanisms that regulate human reproduction. Despite the demonstrated linkage between lactation and return of the first post-partum menses, many questions regarding the relationship between variation in breastfeeding behavior and variation in ovarian function remain unanswered. In particular, women of seemingly comparable breastfeeding magnitude display substantial heterogeneity in the duration of post-partum subfecundity. In addition, the hormonal mechanisms by which lactation regulates ovarian function remain unclear, and the debates regarding the contribution of factors other than breastfeeding to post-partum subfecundity continue unresolved. Part of the difficulty in addressing these questions derives from the use of disparate methodological approaches and an absence of specificity in analytical units. In particular, maternal recall of breastfeeding behavior is subject to substantial bias yet is the data source for most analyses. In addition, although a growing body of evidence suggests that variation in breastfeeding structure may contribute to variation in ovarian function, most studies fail to distinguish or evaluate the different components of suckling behavior. Elucidating the bases of this variation amongst women and populations requires disentangling the roles of the environment, culture, and behavior in structuring suckling activity. Anthropologists in particular have an opportunity to achieve significant insights into the ecology of human breastfeeding and reproduction. © 1994 Wiley-Liss, Inc.