Is Female Health Cyclical? Evolutionary Perspectives on Menstruation

Why do some females menstruate at all? Answering this question has implications for understanding the tight links between reproductive function and organismal immunity. Here we build on the growing evidence that menstruation is the by-product of a "choosy" uterus to (i) make the theoretical case for the idea that female immunity is cyclical in menstruating species, (ii) evaluate the evidence for the menstrual modulation of immunity and health in humans and (iii) speculate on the implications of cyclical female health for female behaviour, male immunity and host-pathogen interactions. We argue that an understanding of females' evolved reproductive system is foundational for both tackling the future challenges of the global women's health agenda and predicting eco-evolutionary dynamics in cyclically reproducing species

The life-history trade-off between fertility and child survival.

Evolutionary models of human reproduction argue that variation in fertility can be understood as the local optimization of a life-history trade-off between offspring quantity and 'quality'. Child survival is a fundamental dimension of quality in these models as early-life mortality represents a crucial selective bottleneck in human evolution. This perspective is well-rehearsed, but current literature presents mixed evidence for a trade-off between fertility and child survival, and little empirical ground to evaluate how socioecological and individual characteristics influence the benefits of fertility limitation. By compiling demographic survey data, we demonstrate robust negative relationships between fertility and child survival across 27 sub-Saharan African countries. Our analyses suggest this relationship is primarily accounted for by offspring competition for parental investment, rather than by reverse causal mechanisms. We also find that the trade-off increases in relative magnitude as national mortality declines and maternal somatic (height) and extrasomatic (education) capital increase. This supports the idea that socioeconomic development, and associated reductions in extrinsic child mortality, favour reduced fertility by increasing the relative returns to parental investment. Observed fertility, however, falls considerably short of predicted optima for maximizing total offspring survivorship, strongly suggesting that additional unmeasured costs of reproduction ultimately constrain the evolution of human family size

The evolutionary ecology of age at natural menopause: implications for public health

Evolutionary perspectives on menopause have focused on explaining why early reproductive cessation in females has emerged and why it is rare throughout the animal kingdom, but less attention has been given to exploring patterns of diversity in age at natural menopause. In this paper, we aim to generate new hypotheses for understanding human patterns of diversity in this trait, defined as age at final menstrual period. To do so, we develop a multilevel, interdisciplinary framework, combining proximate, physiological understandings of ovarian ageing with ultimate, evolutionary perspectives on ageing. We begin by reviewing known patterns of diversity in age at natural menopause in humans, and highlight issues in how menopause is currently defined and measured. Second, we consider together ultimate explanations of menopause timing and proximate understandings of ovarian ageing. We find that ovarian ageing is highly constrained by ageing of the follicle – the somatic structure containing the oocyte – suggesting that menopause timing might be best understood as a by-product of ageing rather than a facultative adaptation. Third, we investigate whether the determinants of somatic senescence also underpin menopause timing. We show that diversity in age at menopause can be, at least partly, explained by the genetic, ecological and life-history determinants of somatic ageing. The public health implications of rethinking menopause as the by-product rather than the catalyst of biological ageing are discussed

The COVID-19 pandemic and the menstrual cycle: research gaps and opportunities

International audienceSince the beginning of the COVID-19 pandemic, discussions on social media and blogs have indicated that women have experienced menstrual changes, including altered menstrual duration, frequency, regularity, and volume (heavier bleeding and clotting), increased dysmenorrhea, and worsened premenstrual syndrome. There have been a small number of scientific studies of variable quality reporting on menstrual cycle features during the pandemic, but it is still unclear whether apparent changes are due to COVID-19 infection/illness itself, or other pandemic-related factors like increased psychological stress and changes in health behaviours. It is also unclear to what degree current findings are explained by reporting bias, recall bias, selection bias and confounding factors. Further research is urgently needed. We provide a list of outstanding research questions and potential approaches to address them. Findings can inform policies to mitigate against gender inequalities in health and society, allowing us to build back better post-COVID

The changing climates of global health.

The historical trajectories of three crises have converged in the 2020s: the COVID-19 pandemic, rising inequality and the climate crisis. Global health as an organising logic is being transformed by the COVID-19 pandemic. We point to an emerging consensus that the triple threats of global heating, zoonoses and worsening, often racialised inequalities, will need to be met by models of cooperation, equitable partnership and accountability that do not sustain exploitative logic of economic growth. Health governance is challenged to reconsider sustainability and justice in terms of how local and global, domestic and transnational, chronic and infectious, human and non-human are interdependent. In this article, we discuss their intersection and suggest that a new set of organising ideals, institutions and norms will need to emerge from their conjunction if a just and liveable world is to remain a possibility for humans and their cohabitants. Future health governance will need to integrate pandemic preparedness, racial justice, inequality and more-than-human life in a new architecture of global health. Such an agenda might be premised on solidarities that reach across national, class, spatial and species divisions, acknowledge historical debts and affirm mutual interdependencies

Kinship ties across the lifespan in human communities

A hypothesis for the evolution of long post-reproductive lifespans in the human lineage involves asymmetries in relatedness between young immigrant females and the older females in their new groups. In these circumstances, inter-generational reproductive conflicts between younger and older females are predicted to resolve in favour of the younger females, who realize fewer inclusive fitness benefits from ceding reproduction to others. This conceptual model anticipates that immigrants to a community initially have few kin ties to others in the group, gradually showing greater relatedness to group members as they have descendants who remain with them in the group. We examine this prediction in a cross-cultural sample of communities, which vary in their sex-biased dispersal patterns and other aspects of social organization. Drawing on genealogical and demographic data, the analysis provides general but not comprehensive support for the prediction that average relatedness of immigrants to other group members increases as they age. In rare cases, natal members of the community also exhibit age-related increases in relatedness. We also find large variation in the proportion of female group members who are immigrants, beyond simple traditional considerations of patrilocality or matrilocality, which raises questions about the circumstances under which this hypothesis of female competition are met. We consider possible explanations for these heterogenous results, and we address methodological considerations that merit increased attention for research on kinship and reproductive conflict in human societies. This article is part of the theme issue 'The evolution of female-biased kinship in humans and other mammals'

Social Transmission and the Spread of Modern Contraception in Rural Ethiopia

Socio-economic development has proven to be insufficient to explain the time and pace of the human demographic transition. Shifts to low fertility norms have thus been thought to result from social diffusion, yet to date, micro-level studies are limited and are often unable to disentangle the effect of social transmission from that of extrinsic factors. We used data which included the first ever use of modern contraception among a population of over 900 women in four villages in rural Ethiopia, where contraceptive prevalence is still low (<20%). We investigated whether the time of adoption of modern contraception is predicted by (i) the proportion of ever-users/non ever-users within both women and their husbands' friendships networks and (ii) the geographic distance to contraceptive ever-users. Using a model comparison approach, we found that individual socio-demographic characteristics (e.g. parity, education) and a religious norm are the most likely explanatory factors of temporal and spatial patterns of contraceptive uptake, while the role of person-to-person contact through either friendship or spatial networks remains marginal. Our study has broad implications for understanding the processes that initiate transitions to low fertility and the uptake of birth control technologies in the developing world

Cultural Evolution and Population Health Interventions

International audienceCulture is often invoked as an explanation for disparities in health or as a barrier to success in population health interventions, yet the micro-level processes underpinning cultural inertia and cultural epidemics are rarely unpacked. By contrast, a cultural evolution framework breaks down “culture” as a population of cultural variants and focuses on uncovering the social learning “strategies” and individual motivations leading to behavioural variation and change. Here I elaborate on how thinking evolutionarily can help understand the bidirectional relationship between behaviour and culture, thereby shedding light on the processes leading to the adoption, transmission, and maintenance of behaviour over time and across socio-ecological contexts. I begin with introducing the concept of culture in epidemiology as well as contemporary evolutionary approaches to culture. I then consider how a cultural evolution framework can be deployed at various levels of interventions, from health-message framing and norms-based messaging to social network and communities-based interventions. Lastly, I evaluate how a cultural evolution framework can be harnessed to tackle public health challenges, including how to seed a new healthy behaviour, how to spread behaviour beyond its initial uptake and how to maintain behaviour in the face of changing ecologies. While cultural evolution (CE) studies of population health (PH) issues are currently limited, there is a large scope for CE and PH to mutually benefit from joining forces

Cultural Evolution and Population Health Interventions

International audienceCulture is often invoked as an explanation for disparities in health or as a barrier to success in population health interventions, yet the micro-level processes underpinning cultural inertia and cultural epidemics are rarely unpacked. By contrast, a cultural evolution framework breaks down “culture” as a population of cultural variants and focuses on uncovering the social learning “strategies” and individual motivations leading to behavioural variation and change. Here I elaborate on how thinking evolutionarily can help understand the bidirectional relationship between behaviour and culture, thereby shedding light on the processes leading to the adoption, transmission, and maintenance of behaviour over time and across socio-ecological contexts. I begin with introducing the concept of culture in epidemiology as well as contemporary evolutionary approaches to culture. I then consider how a cultural evolution framework can be deployed at various levels of interventions, from health-message framing and norms-based messaging to social network and communities-based interventions. Lastly, I evaluate how a cultural evolution framework can be harnessed to tackle public health challenges, including how to seed a new healthy behaviour, how to spread behaviour beyond its initial uptake and how to maintain behaviour in the face of changing ecologies. While cultural evolution (CE) studies of population health (PH) issues are currently limited, there is a large scope for CE and PH to mutually benefit from joining forces

Why we must fight ignorance about COVID-19 vaccines and menstrual cycles

International audienceThe COVID-19 pandemic has revealed a critical gap in the female health science, fueling anxiety, polarized views, and vaccine hesitancy. Although menstrual cycles feel like a “niche topic” for some, efforts to augment knowledge on the “5th vital sign” experienced by 300 million people worldwide are crucial to promote gender equity in health