Why we must fight ignorance about COVID-19 vaccines and menstrual cycles.
September 2023
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Journal article
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Trends in molecular medicine
The COVID-19 pandemic has revealed a critical gap in 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 'fifth vital sign' experienced by more than 300 million people on any given day worldwide are crucial to promote gender equity in health.
A retrospective case-control study on menstrual cycle changes following COVID-19 vaccination and disease
March 2023
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Journal article
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iScience
There has been increasing public concern that COVID-19 vaccination causes menstrual disturbance regarding the relative effect of vaccination compared to SARS-CoV-2 infection. Our objectives were to test potential risk factors for reporting menstrual cycle changes following COVID-19 vaccination and to compare menstrual parameters following COVID-19 vaccination and COVID-19 disease. We performed a secondary analysis of a retrospective online survey conducted in the UK in March 2021. In pre-menopausal vaccinated participants (n=4,989), 18% reported menstrual cycle changes after their first COVID-19 vaccine injection. The prevalence of reporting any menstrual changes was higher for women who smoke, have a history of COVID-19 disease, or are not using oestradiol-containing contraceptives. In a second sample including both vaccinated and unvaccinated participants (n=12,579), COVID-19 vaccination alone was not associated with abnormal menstrual cycle parameters while a history of COVID-19 disease was associated with an increased risk of reporting heavier bleeding, ‘missed’ periods and inter-menstrual bleeding.
FFR
Integrating the environmental and genetic architectures of mortality and aging
January 2023
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preprint
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medRxiv
Anemic Women are More at Risk of Injectable Contraceptive Discontinuation due to Side Effects in Ethiopia.
March 2022
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Journal article
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Studies in family planning
This paper investigates the importance of women's physiological condition, alongside sociocultural factors, for predicting the risk of discontinuation of the injectable contraceptive due to side effects in Ethiopia. Contraceptive calendar data from the 2016 Ethiopian Demographic and Health Survey were analyzed. Women aged 15-49 who had initiated the injectable contraceptive in the last two years were included in the analysis (n = 1,513). Physiological factors investigated were body mass, iron status, reproductive depletion, and physical strain. After checking for reverse causality, associations between physiological and sociocultural risk factors and discontinuation due to side effects (DSE) or discontinuation due to other reasons (DOR) were estimated using multivariate Cox proportional regression analyses. Anemia status was associated with DSE, but not DOR. Anemic women were two times more at risk of DSE compared with nonanemic women (adjusted hazard ratios [aHR] = 2.38, confidence interval [CI] = 1.41-4.00). DOR was predicted by religion, wealth, and relationship status. Accounting for diversity in physiological condition is key for understanding contraceptive discontinuation due to side effects. To reduce side effects, family planning programs might benefit from providing hormonal contraception within an integrated package addressing anemia.
COVID-19 vaccination and menstrual cycle changes: A United Kingdom (UK) retrospective case-control study
January 2021
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preprint
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medRxiv
Cultural change beyond adoption dynamics: Evolutionary approaches to the discontinuation of contraception.
January 2021
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Journal article
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Evolutionary human sciences
Numerous evolutionary mechanisms have been proposed for the origins, spread and maintenance of low fertility. Such scholarship has focused on explaining the adoption of fertility-reducing behaviour, especially the use of contraceptive methods. However, this work has yet to engage fully with the dynamics of contraceptive behaviour at the individual level. Here we highlight the importance of considering not just adoption but also discontinuation for understanding contraceptive dynamics and their impact on fertility. We start by introducing contemporary evolutionary approaches to understanding fertility regulation behaviours, discussing the potential for integrating behavioural ecology and cultural evolution frameworks. Second, we draw on family planning studies to highlight the importance of contraceptive discontinuation owing to side-effects for understanding fertility rates and suggest evolutionary hypotheses for explaining patterns of variation in discontinuation rates. Third, we sketch a framework for considering how individual flexibility in contraceptive behaviour might impact the evolution of contraceptive strategies and the demographic transition. We argue that integrating public health and evolutionary approaches to reproductive behaviour might advance both fields by providing (a) a predictive framework for comparing the effectiveness of various public health strategies and (b) a more realistic picture of behaviour by considering contraceptive dynamics at the individual level more explicitly when modelling the cultural evolution of low fertility.
Reinterpreting patterns of variation in human thyroid function: An evolutionary ecology perspective.
January 2021
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Journal article
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Evolution, medicine, and public health
Two hundred million people worldwide experience some form of thyroid disorder, with women being especially at risk. However, why human thyroid function varies between populations, individuals, and across the lifespan has attracted little research to date. This limits our ability to evaluate the conditions under which patterns of variation in thyroid function are best understood as 'normal' or 'pathological'. In this review, we aim to spark interest in research aimed at understanding the causes of variation in thyroid phenotypes. We start by assessing the biomedical literature on thyroid imbalance to discuss the validity of existing reference intervals for diagnosis and treatment across individuals and populations. We then propose an evolutionary ecological framework for understanding the phylogenetic, genetic, ecological, developmental, and physiological causes of normal variation in thyroid function. We build on this approach to suggest testable predictions for how environmental challenges interact with individual circumstances to influence the onset of thyroid disorders. We propose that dietary changes, ecological disruptions of co-evolutionary processes during pregnancy and with pathogens, emerging infections, and exacerbated stress responses can contribute to explaining the onset of thyroid diseases. For patients to receive the best personalized care, research into the causes of thyroid variation at multiple levels is needed.
Anaemic women are more at risk of injectable contraceptive discontinuation due to side-effects in Ethiopia
January 2020
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preprint
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medRxiv
The evolutionary ecology of age at natural menopause: implications for public health.
January 2020
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Journal article
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Evolutionary human sciences
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.
Can postfertile life stages evolve as an anticancer mechanism?
December 2019
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Journal article
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PLoS Biology
Why a postfertile stage has evolved in females of some species has puzzled evolutionary biologists for over 50 years. We propose that existing adaptive explanations have underestimated in their formulation an important parameter operating both at the specific and the individual levels: the balance between cancer risks and cancer defenses. During their life, most multicellular organisms naturally accumulate oncogenic processes in their body. In parallel, reproduction, notably the pregnancy process in mammals, exacerbates the progression of existing tumors in females. When, for various ecological or evolutionary reasons, anticancer defenses are too weak, given cancer risk, older females could not pursue their reproduction without triggering fatal metastatic cancers, nor even maintain a normal reproductive physiology if the latter also promotes the growth of existing oncogenic processes, e.g., hormone-dependent malignancies. At least until stronger anticancer defenses are selected for in these species, females could achieve higher inclusive fitness by ceasing their reproduction and/or going through menopause (assuming that these traits are easier to select than anticancer defenses), thereby limiting the risk of premature death due to metastatic cancers. Because relatively few species experience such an evolutionary mismatch between anticancer defenses and cancer risks, the evolution of prolonged life after reproduction could also be a rare, potentially transient, anticancer adaptation in the animal kingdom.
FFR
Kinship ties across the lifespan in human communities
July 2019
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Journal article
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Philosophical Transactions B: Biological Sciences
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.
life history theory, kinship, reproductive conflict, residence, dispersal, descent
Stochastic dynamics of an epidemic with recurrent spillovers from an endemic reservoir.
November 2018
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Journal article
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Journal of theoretical biology
Most emerging human infectious diseases have an animal origin. While zoonotic diseases originate from a reservoir, most theoretical studies have principally focused on single-host processes, either exclusively humans or exclusively animals, without considering the importance of animal to human transmission (i.e. spillover transmission) for understanding the dynamics of emerging infectious diseases. Here we aim to investigate the importance of spillover transmission for explaining the number and the size of outbreaks. We propose a simple continuous time stochastic Susceptible-Infected-Recovered model with a recurrent infection of an incidental host from a reservoir (e.g. humans by a zoonotic species), considering two modes of transmission, (1) animal-to-human and (2) human-to-human. The model assumes that (i) epidemiological processes are faster than other processes such as demographics or pathogen evolution and that (ii) an epidemic occurs until there are no susceptible individuals left. The results show that during an epidemic, even when the pathogens are barely contagious, multiple outbreaks are observed due to spillover transmission. Overall, the findings demonstrate that the only consideration of direct transmission between individuals is not sufficient to explain the dynamics of zoonotic pathogens in an incidental host.
Humans are still evolving, but we need more than evolutionary genetics to predict our future
September 2018
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Journal article
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Trends in Ecology and Evolution
What may become of Homo sapiens? If you are looking for confirmation that the future of humanity is doomed, or that ‘all men will have big willies’ [1] as predicted by The Sun (a British tabloid), this book is not for you. But if what you want is an evidence-based assessment of what the evolutionary human sciences can – and cannot – contribute to our understanding of the future of human evolution, this is a good place to start.
Do sexually transmitted infections exacerbate negative premenstrual symptoms? Insights from digital health
July 2018
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Journal article
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Evolution, Medicine, and Public Health
<strong>Background and objectives</strong> The underlying reasons why some women experience debilitating premenstrual symptoms and others do not are largely unknown. Here we test the evolutionary ecological hypothesis that some negative premenstrual symptoms may be exacerbated by the presence of chronic sexually transmitted infections (STIs). <strong>Methodology</strong> 34,511 women were recruited through a digital period-tracker app. Participants were asked: (i) Have you ever been diagnosed with a STI? (ii) If yes, when was it, and were you given treatment? Those data were combined with longitudinal cycle data on menstrual bleeding patterns, the experience of pain and emotions and hormonal contraceptive use. <strong>Results</strong> 865 women had at least two complete menstrual cycle data and were eligible for analysis. Before diagnosis, the presence of an infection predicts a ca. two-fold increase in the odds of reporting both headache, cramps and sadness during the late luteal phase and sensitive emotions during the wider luteal phase. After diagnosis, the odds of reporting negative symptoms pre-menstrually remain unchanged among STI negative individuals, but the odds of reporting sensitive emotions decrease among STI positive individuals receiving a treatment. No relationships between STIs, pain and emotions are observed among hormonal contraceptive users. <strong>Conclusions and implications</strong> The results support the idea that a negative premenstrual experience might be aggravated by the presence of undiagnosed STIs, a leading cause of infertility worldwide. Caution is warranted in extrapolating the results as the data are self-reported, inflammatory levels are unknown and the tracker is biased towards recording negative premenstrual symptoms among Western individuals.
evolutionary immunobiology, reproduction and hormones
Is female health cyclical? evolutionary perspectives on menstruation
May 2018
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Journal article
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Trends in Ecology and Evolution
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 byproduct 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.
pathogen evolution, menstrual cycle, inflammation, ecoimmunology, evolutionary medicine and public health, reproduction-immunity trade-offs
Stochasticity in cultural evolution: a revolution yet to happen.
November 2017
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Journal article
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History and Philosophy of the Life Sciences
Over the last 40 years or so, there has been an explosion of cultural evolution research in anthropology and archaeology. In each discipline, cultural evolutionists investigate how interactions between individuals translate into group level patterns, with the aim of explaining the diachronic dynamics and diversity of cultural traits. However, while much attention has been given to deterministic processes (e.g. cultural transmission biases), we contend that current evolutionary accounts of cultural change are limited because they do not adopt a systematic stochastic approach (i.e. accounting for the role of chance). First, we show that, in contrast with the intense debates in ecology and population genetics, the importance of stochasticity in evolutionary processes has generated little discussion in the sciences of cultural evolution to date. Second, we speculate on the reasons, both ideological and methodological, why that should be so. Third, we highlight the inadequacy of genetically-inspired stochastic models in the context of cultural evolution modelling, and ask which fundamental stochastic processes might be more relevant to take up. We conclude that the field of cultural evolution would benefit from a stochastic revolution. For that to occur, stochastic models ought to be developed specifically for cultural data and not through a copy-pasting of neutral models from population genetics or ecology.
Stochastic processes, Population genetics, Anthropology, Population ecology, Cultural evolution, Archaeology
Side effects and the need for secrecy: characterising discontinuation of modern contraception and its causes in Ethiopia using mixed methods
October 2017
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Journal article
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Contraception and Reproductive Medicine
<p><b>Background:</b> Contraceptive discontinuation is a major barrier to reducing global unmet needs for family planning, but the reasons why women discontinue contraception are poorly understood. Here we use data from Ethiopia to investigate (i) the magnitude of contraceptive discontinuation in 2005-2011, (ii) how the risk of discontinuation varies with method type and education level and (iii) the barriers to continuation. Our main hypothesis is that contraceptive discontinuation is driven by the experience of physiological side-effects associated with the use of hormonal contraception, rather than a lack of formal education. </p><p><b>Methods:</b> We used a mixed methods explanatory sequential design to explain the quantitative results in more details through the qualitative data. First, we analysed quantitative data from the 2011 Ethiopian Demographic and Health Survey to study patterns of contraceptive discontinuation and method choice using multilevel multiprocess models. Second, we conducted semi-structured interviews and focus group discussions in the 3 most populated regions of Ethiopia with individuals of reproductive age and health professionals. </p><p><b>Results:</b> The analysis of EDHS data shows that the rate of discontinuation has not reduced in the period 2005-2011 and remains high. Discontinuation mainly takes the form of abandonment, and is a function of method type, age and wealth but not of educational level. Interviews with women and health professionals reveal that the experience of debilitating physiological side effects, the need for secrecy and poverty are important barriers to continuation. </p><p><b>Conclusions:</b> Our findings together suggest that physiological and social side-effects of contraceptive use, not a lack of formal education, are the root causes of contraceptive abandonment in Ethiopia. </p>
Side effects and the need for secrecy: characterising discontinuation of modern contraception and its causes in Ethiopia using mixed methods
January 2017
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preprint
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bioRxiv
Evolutionary Thinking in Medicine From Research to Policy and Practice
May 2016
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Book
The aim of this edited book is to provide health professionals, across a wide variety of specialisms, with a targeted access to evolutionary medicine.
Medical
Correction: Beyond Rational Decision-Making: Modelling the Influence of Cognitive Biases on the Dynamics of Vaccination Coverage.
January 2016
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Journal article
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PloS one
[This corrects the article DOI: 10.1371/journal.pone.0142990.].
Beyond rational decision-making: modelling the influence of cognitive biases on the dynamics of vaccination coverage
January 2015
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Journal article
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PLoS One
<strong>Background:</strong> Theoretical studies predict that it is not possible to eradicate a disease under voluntary vaccination because of the emergence of non-vaccinating “free-riders” when vaccination coverage increases. A central tenet of this approach is that human behaviour follows an economic model of rational choice. Yet, empirical studies reveal that vaccination decisions do not necessarily maximize individual self-interest. Here we investigate the dynamics of vaccination coverage using an approach that dispenses with payoff maximization and assumes that risk perception results from the interaction between epidemiology and cognitive biases. <strong>Methods:</strong> We consider a behaviour-incidence model in which individuals perceive actual epidemiological risks as a function of their opinion of vaccination. As a result of confirmation bias, sceptical individuals (negative opinion) overestimate infection cost while pro-vaccines individuals (positive opinion) overestimate vaccination cost. We considered a feedback between individuals and their environment as individuals could change their opinion, and thus the way they perceive risks, as a function of both the epidemiology and the most common opinion in the population. <strong>Results:</strong> For all parameter values investigated, the infection is never eradicated under voluntary vaccination. For moderately contagious diseases, oscillations in vaccination coverage emerge because individuals process epidemiological information differently depending on their opinion. Conformism does not generate oscillations but slows down the cultural response to epidemiological change. <strong>Conclusion:</strong> Failure to eradicate vaccine preventable disease emerges from the model because of cognitive biases that maintain heterogeneity in how people perceive risks. Thus, assumptions of economic rationality and payoff maximization are not mandatory for predicting commonly observed dynamics of vaccination coverage. This model shows that alternative notions of rationality, such as that of ecological rationality whereby individuals use simple cognitive heuristics, offer promising new avenues for modelling vaccination behaviour.
Evolutionary Medicine
January 2015
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Chapter
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International Encyclopedia of the Social & Behavioral Sciences
50 Philosophy and Religious Studies, 5002 History and Philosophy Of Specific Fields, Cancer, Biotechnology, Generic health relevance, 3 Good Health and Well Being
Ecological variation in wealth–fertility relationships in Mongolia: the ‘central theoretical problem of sociobiology’ not a problem after all?
December 2014
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Journal article
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Proceedings of the Royal Society B: Biological Sciences
The negative wealth–fertility relationship brought about by market integration remains a puzzle to classic evolutionary models. Evolutionary ecologists have argued that this phenomenon results from both stronger trade-offs between reproductive and socioeconomic success in the highest social classes and the comparison of groups rather than individuals. Indeed, studies in contemporary low fertility settings have typically used aggregated samples that may mask positive wealth–fertility relationships. Furthermore, while much evidence attests to trade-offs between reproductive and socioeconomic success, few studies have explicitly tested the idea that such constraints are intensified by market integration. Using data from Mongolia, a post-socialist nation that underwent mass privatization, we examine wealth–fertility relationships over time and across a rural–urban gradient. Among post-reproductive women, reproductive fitness is the lowest in urban areas, but increases with wealth in all regions. After liberalization, a demographic–economic paradox emerges in urban areas: while educational attainment negatively impacts female fertility in all regions, education uniquely provides socioeconomic benefits in urban contexts. As market integration progresses, socio-economic returns to education increase and women who limit their reproduction to pursue education get wealthier. The results support the view that selection favoured mechanisms that respond to opportunities for status enhancement rather than fertility maximization.
Associations between family size and offspring education depend on aspects of parental personality
February 2014
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Journal article
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Personality and Individual Differences
5202 Biological Psychology, 5205 Social and Personality Psychology, 52 Psychology, Behavioral and Social Science, 2.3 Psychological, social and economic factors, 2 Aetiology, 4 Quality Education
Identification of visual paternity cues in humans.
January 2014
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Journal article
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Biology letters
Understanding how individuals identify their relatives has implications for the evolution of social behaviour. Kinship cues might be based on familiarity, but in the face of paternity uncertainty and costly paternal investment, other mechanisms such as phenotypic matching may have evolved. In humans, paternal recognition of offspring and subsequent discriminative paternal investment have been linked to father-offspring facial phenotypic similarities. However, the extent to which paternity detection is impaired by environmentally induced facial information is unclear. We used 27 portraits of fathers and their adult sons to quantify the level of paternity detection according to experimental treatments that manipulate the location, type and quantity of visible facial information. We found that (i) the lower part of the face, that changes most with development, does not contain paternity cues, (ii) paternity can be detected even if relational information within the face is disrupted and (iii) the signal depends on the presence of specific information rather than their number. Taken together, the results support the view that environmental effects have little influence on the detection of paternity using facial similarities. This suggests that the cognitive dispositions enabling the facial detection of kinship relationships ignore genetic irrelevant facial information.
Fertility, parental investment, and the early adoption of modern contraception in rural Ethiopia.
January 2013
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Journal article
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American journal of human biology : the official journal of the Human Biology Council
ObjectivesWhat triggers initial shifts to fertility limitation as populations undergo socioeconomic development remains poorly understood. Alternative models emphasize the social contagion of low fertility ideals, or the individual perception of economic and/or fitness benefits to fertility limitation. Few micro-level studies in communities experiencing the earliest stages of the demographic transition are available. In a previous study, we found little support for the role of social transmission through friendships and spatial networks in explaining contraceptive uptake in rural Ethiopia, where contraceptive prevalence is low (800 women which recorded fertility, birth spacing and offspring survivorship. We first investigated whether ever-users and non-users differ in their reproductive behavior and success prior to contraception use. We then conducted a within-women analysis to investigate the impact of contraceptive uptake on reproduction and child survivorship.ResultsWomen who have experienced higher fertility and higher child survival adopt modern contraception sooner rather than later, and contraceptive use among early adopters is predictive of greater birth spacing. However, contraceptive uptake does not have an impact on offspring survivorship.ConclusionsOur data provide support for the idea that preferences for low fertility emerge in response to increasing competition between offspring. The study has implications for our understanding of the emergence of local fertility norms and the spread of modern birth control.
The life-history trade-off between fertility and child survival.
December 2012
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Journal article
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Proceedings. Biological sciences
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.
Humans, Child Mortality, Family Characteristics, Marital Status, Parents, Maternal Age, Demography, Fertility, Socioeconomic Factors, Adolescent, Adult, Child, Preschool, Infant, Africa South of the Sahara, Female, Male, Young Adult, Biological Evolution
Facial attractiveness and fertility in populations with low levels of modern birth control
September 2012
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Journal article
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Evolution and Human Behavior
5202 Biological Psychology, 5205 Social and Personality Psychology, 52 Psychology, Contraception/Reproduction, Reproductive health and childbirth, 3 Good Health and Well Being
Female reproductive competition within families in rural Gambia.
June 2012
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Journal article
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Proceedings. Biological sciences
Many studies show that the extended human family can be helpful in raising offspring, with maternal grandmothers, in particular, improving offspring survival. However, less attention has been given to competition between female kin and co-residents. It has been argued that reproductive conflict between generations explains the evolution of menopause in cooperatively breeding species where females disperse, and that older females are related to the offspring of younger females through their sons, whereas younger, incoming females are unrelated to older females. This means the pattern of help will be asymmetric, so older females lose in reproductive conflict and become 'sterile helpers'. Here, we seek evidence for female reproductive competition using longitudinal demographic data from a rural Gambian population, and examine when women are helping or harming each other's reproductive success. We find that older women benefit and younger women suffer costs of reproductive competition with women in their compound. But the opposite is found for mothers and daughters; if mother and daughter's reproductive spans overlap, the older woman reduces her reproduction if the younger woman (daughter) reproduces, whereas daughters' fertility is unaffected by their mothers' reproduction. Married daughters are not generally co-resident with their mothers, so we find not only competition effects with co-resident females, but also with daughters who have dispersed. Dispersal varies across human societies, but our results suggest reproductive conflict could be influencing reproductive scheduling whatever the dispersal pattern. A cultural norm of late male marriage reduces paternal grandmother/daughter-in-law reproductive overlap almost to zero in this population. We argue that cultural norms surrounding residence and marriage are themselves cultural adaptations to reduce reproductive conflict between generations in human families.
Men's preference for women's facial features: testing homogamy and the paternity uncertainty hypothesis.
January 2012
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Journal article
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PloS one
Male mate choice might be based on both absolute and relative strategies. Cues of female attractiveness are thus likely to reflect both fitness and reproductive potential, as well as compatibility with particular male phenotypes. In humans, absolute clues of fertility and indices of favorable developmental stability are generally associated with increased women's attractiveness. However, why men exhibit variable preferences remains less studied. Male mate choice might be influenced by uncertainty of paternity, a selective factor in species where the survival of the offspring depends on postnatal paternal care. For instance, in humans, a man might prefer a woman with recessive traits, thereby increasing the probability that his paternal traits will be visible in the child and ensuring paternity. Alternatively, attractiveness is hypothesized to be driven by self-resembling features (homogamy), which would reduce outbreeding depression. These hypotheses have been simultaneously evaluated for various facial traits using both real and artificial facial stimuli. The predicted preferences were then compared to realized mate choices using facial pictures from couples with at least 1 child. No evidence was found to support the paternity uncertainty hypothesis, as recessive features were not preferred by male raters. Conversely, preferences for self-resembling mates were found for several facial traits (hair and eye color, chin dimple, and thickness of lips and eyebrows). Moreover, realized homogamy for facial traits was also found in a sample of long-term mates. The advantages of homogamy in evolutionary terms are discussed.
Humans, Family Characteristics, Marriage, Family Relations, Choice Behavior, Reproduction, Fertility, Paternity, Adolescent, Adult, Female, Male
Reproductive behavior and personality traits of the Five Factor Model
November 2011
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Journal article
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European Journal of Personality
3101 Biochemistry and Cell Biology, 32 Biomedical and Clinical Sciences, 31 Biological Sciences, 3202 Clinical Sciences, 3209 Neurosciences, Behavioral and Social Science, Basic Behavioral and Social Science, Contraception/Reproduction, Reproductive health and childbirth
Left-handedness and male-male competition: insights from fighting and hormonal data.
August 2011
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Journal article
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Evolutionary psychology : an international journal of evolutionary approaches to psychology and behavior
Male-male competition can shape some behavioral or morphological traits of males. Here we investigate if this competition could play a role in the persistence of the polymorphism of handedness in human populations. A negative frequency-dependent selection mechanism has been hypothesized, based on the fact that left-handed men may benefit from a "surprise" advantage during fighting interactions because they are rare in human populations. This advantage may thereby enhance the probability of survival of left- handed men and/or their reproductive success through an increase in social status. In this study, we first explored the association between hand preference and lifetime fighting behavior in a population of 1,161 French men. No effect of hand preference on the probability of fighting was detected, suggesting that the innate propensity to fight does not differ between left- and right-handers. However, among men who had been involved in at least one fight during their lifetime, left-handers reported significantly more fights than right-handers. To explore the biological basis of this behavior, we also investigated the testosterone concentration in saliva samples from 64 French university students. Consistent with frequencies of fights, we found a significantly higher average testosterone concentration in left-handers than in right-handers. We suggest that these behavioral and hormonal differences may be acquired throughout life due to previous experiences in a social context and may favor the persistence of left-handers in humans.
Saliva, Humans, Testosterone, Cohort Studies, Aggression, Competitive Behavior, Students, Adult, Middle Aged, France, Male, Functional Laterality, Young Adult, Surveys and Questionnaires
Mothers and Others: The Evolutionary Origins of Mutual Understanding. By Sarah Blaffer Hrdy. Pp. 422. (Harvard University Press, Cambridge, MA, USA, 2009.) £19.95, ISBN 978-0-674-03299-6, hardback.
July 2011
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Journal article
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Journal of Biosocial Science
4404 Development Studies, 44 Human Society
Social transmission and the spread of modern contraception in rural Ethiopia.
January 2011
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Journal article
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PloS one
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 (
Humans, Contraception, Interpersonal Relations, Perception, Decision Making, Diffusion, Models, Theoretical, Time Factors, Social Support, Adolescent, Adult, Middle Aged, Rural Population, Ethiopia, Female, Male, Young Adult
Personality and testosterone in men from a high-fertility population
December 2010
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Journal article
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Personality and Individual Differences
5202 Biological Psychology, 5205 Social and Personality Psychology, 52 Psychology, Behavioral and Social Science, Contraception/Reproduction
Response to Carere et al. Human mate preference: inconsistency between data and interpretations
September 2010
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Journal article
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Trends in Ecology & Evolution
31 Biological Sciences, 41 Environmental Sciences
Personality and reproductive success in a high-fertility human population.
June 2010
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Journal article
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Proceedings of the National Academy of Sciences of the United States of America
The existence of interindividual differences in personality traits poses a challenge to evolutionary thinking. Although research on the ultimate consequences of personality differences in nonhuman animals has recently undergone a surge of interest, our understanding of whether and how personality influences reproductive decisions in humans has remained limited and informed primarily by modern societies with low mortality-fertility schedules. Taking an evolutionary approach, we use data from a contemporary polygynous high-fertility human population living in rural Senegal to investigate whether personality dimensions are associated with key life-history traits in humans, i.e., quantity and quality of offspring. We show that personality dimensions predict reproductive success differently in men and women in such societies and, in women, are associated with a trade-off between offspring quantity and quality. In women, neuroticism positively predicts the number of children, both between and within polygynous families. Furthermore, within the low social class, offspring quality (i.e., child nutritional status) decreases with a woman's neuroticism, indicating a reproductive trade-off between offspring quantity and quality. Consistent with this, maximal fitness is achieved by women at an intermediate neuroticism level. In men, extraversion was found to be a strong predictor of high social class and polygyny, with extraverted men producing more offspring than their introverted counterparts. These results have implications for the consideration of alternative adaptive hypotheses in the current debate on the maintenance of personality differences and the role of individual factors in fertility patterns in contemporary humans.
Detective mice assess relatedness in baboons using olfactory cues.
May 2010
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Journal article
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The Journal of experimental biology
The assessment of relatedness may be crucial in the evolution of socio-sexual behaviour, because it can be associated with fitness benefits mediated by both nepotism and inbreeding avoidance. In this context, one proposed mechanism for kin recognition is 'phenotype matching'; animals might compare phenotypic similarities between themselves and others in order to assess the probability that they are related. Among cues potentially used for kin discrimination, body odours constitute interesting candidates that have been poorly investigated in anthropoid primates so far, because of a mixture of theoretical considerations and methodological/experimental constraints. In this study, we used an indirect approach to examine the similarity in odour signals emitted by related individuals from a natural population of chacma baboons (Papio ursinus). For that purpose, we designed an innovative behavioural tool using mice olfactory abilities in a habituation-discrimination paradigm. We show that: (i) mice can detect odour differences between individuals of same sex and age class in another mammal species, and (ii) mice perceive a higher odour similarity between related baboons than between unrelated baboons. These results suggest that odours may play a role in both the signalling of individual characteristics and of relatedness among individuals in an anthropoid primate. The 'biological olfactometer' developed in this study offers new perspectives to the exploration of olfactory signals from a range of species.
Does the contraceptive pill alter mate choice in humans?
March 2010
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Journal article
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Trends in ecology & evolution
Female and male mate choice preferences in humans both vary according to the menstrual cycle. Women prefer more masculine, symmetrical and genetically unrelated men during ovulation compared with other phases of their cycle, and recent evidence suggests that men prefer ovulating women to others. Such monthly shifts in mate preference have been suggested to bring evolutionary benefits in terms of reproductive success. New evidence is now emerging that taking the oral contraceptive pill might significantly alter both female and male mate choice by removing the mid-cycle change in preferences. Here, we review support for such conclusions and speculate on the consequences of pill-induced choice of otherwise less-preferred partners for relationship satisfaction, durability and, ultimately, reproductive outcomes.
Humans, Contraceptives, Oral, Sexual Behavior, Marriage, Menstrual Cycle, Female, Male
Are parents' perceptions of offspring facial resemblance consistent with actual resemblance? Effects on parental investment
January 2010
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Journal article
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Evolution and Human Behavior
5202 Biological Psychology, 5205 Social and Personality Psychology, 52 Psychology, Behavioral and Social Science, Clinical Research, Pediatric, Mental Health
Variation in testosterone levels and male reproductive effort: insight from a polygynous human population.
November 2009
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Journal article
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Hormones and behavior
Recent evidence suggests that, in humans, variations in testosterone (T) levels between men reflect their differential allocation in mating versus parenting efforts. However, most studies have been conducted in urbanized, monogamous populations, making generalizations from them questionable. This study addresses the question of whether indicators of male reproductive effort are associated with variations in salivary T levels in a polygynous population of agriculturists in rural Senegal. We first show that pair-bonding and/or transition to fatherhood is associated with T profiles: married fathers (N=53) have lower morning and afternoon T levels than unmarried non-fathers (N=28). Second, among fathers, individual differences in parenting effort, as well as variations in mating effort, predict morning T levels. Indeed, men highly investing in parental care show lower morning T levels. Moreover, among men under 50, polygynous men show higher morning T levels than monogamous men. Taken together with previous results in monogamous settings, these findings suggest that the endocrine regulation of reproductive effort is probably a general feature of human populations.
Saliva, Humans, Testosterone, Sexual Behavior, Marriage, Parenting, Paternal Behavior, Fathers, Adaptation, Physiological, Circadian Rhythm, Male
Father–offspring resemblance predicts paternal investment in humans
July 2009
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Journal article
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Animal Behaviour
31 Biological Sciences, 5205 Social and Personality Psychology, 52 Psychology, Clinical Research, Genetics, Pediatric, Behavioral and Social Science, Generic health relevance
Cross-cultural perceptions of facial resemblance between kin.
June 2009
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Journal article
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Journal of vision
Humans use facial comparisons to identify their relatives and adjust their behavior accordingly. However, the mechanisms underlying the assessment of facial similarities are poorly known. Here, we investigate the role of exposure to particular faces for the detection of facial similarities by asking judges to detect parent-child pairs using faces from different origins. In a first phase, French and Senegalese judges assessed facial resemblance in French and Senegalese families. In a second phase, Senegalese judges who had immigrated to France, as well as French and Senegalese stationary judges, were asked to rate a second set of Senegalese and French families. The judges showed no differences in their ability to detect parent-child pairs in French and Senegalese families in both the first and second phases. For judges who changed their country of residence, the answer time and duration of stay in the new country were not associated with correct assignment rates. Our results suggest that exposure has a limited role in the ability to process facial resemblance in others, which contrasts with facial recognition processing. We also discuss whether processing facial similarities is a by-product of the facial recognition system or an evolved ability to assess kinship relationships.
Human Ability to Recognize Kin Visually Within Primates.
February 2009
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Journal article
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International journal of primatology
The assessment of relatedness is a key determinant in the evolution of social behavior in primates. Humans are able to detect kin visually in their own species using facial phenotypes, and facial resemblance in turn influences both prosocial behaviors and mating decisions. This suggests that cognitive abilities that allow facial kin detection in conspecifics have been favored in the species by kin selection. We investigated the extent to which humans are able to recognize kin visually by asking human judges to assess facial resemblance in 4 other primate species (common chimpanzees, western lowland gorillas, mandrills, and chacma baboons) on the basis of pictures of faces. Humans achieved facial interspecific kin recognition in all species except baboons. Facial resemblance is a reliable indicator of relatedness in at least chimpanzees, gorillas, and mandrills, and future work should explore if the primates themselves also share the ability to detect kin facially.
Developmental plasticity of human reproductive development: effects of early family environment in modern-day France.
December 2008
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Journal article
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Physiology & behavior
In a first study, we investigated how the absence of a father and the presence of a stepfather during early childhood affected physiological and behavioral traits related to reproductive development (such as age of menarche, age of first sexual intercourse and number of sexual partners) in a large sample set of male and female French university students. We evaluated which ages were sensitive to modifications in the family composition and found that menarche occurred earlier when the father was absent, particularly when the child was between 0 and 5 years of age. Father absence during early adolescence was associated with a younger age at first sexual intercourse and an increased number of sexual partners, for both sexes. The presence of a stepfather during this period further advanced the age of first sexual intercourse. We also measured testosterone levels in both sexes and analyzed their association with parental separation, and found that young women with separated parents had significantly higher afternoon levels of testosterone. In a second study, we analyzed direct fitness measures (such as number of children and grandchildren) in a large sample of French workers and found that parental separation during childhood was not associated with fitness variation. We discuss whether the reproductive outcomes of individuals having experienced modifications in the early family environment are the expression of costs or adaptive strategies.
Saliva, Humans, Testosterone, Linear Models, Cohort Studies, Sexual Behavior, Adolescent Development, Psychosexual Development, Family Characteristics, Family Relations, Fathers, Sexual Maturation, Reference Values, Social Environment, Adolescent, Adult, Child, Female, Male, Young Adult
Inter-specific kin recognition: Are humans able to identify family relatives among other primate species?
January 2008
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Conference paper
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FOLIA PRIMATOLOGICA
kin recognition, facial resemblance, chacma baboons, chimpanzees, lowland gorillas, mandrills
Differential facial resemblance of young children to their parents: who do children look like more?
March 2007
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Journal article
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Evolution and Human Behavior
5202 Biological Psychology, 5205 Social and Personality Psychology, 52 Psychology, Pediatric, Clinical Research
Handedness and reproductive success in two large cohorts of French adults