This seminar series will explore human behavior from the perspective of evolutionary theory.  It opens with a study of the minds of paper wasps and continues with an exploration of sexual conflict in animals and humans.  Then it delves into features that set humans apart from other species such as religion, cooperation through indirect reciprocity, and runaway social selection. It investigates the causes of obesity and the impact of discrimination and climate change on human behavior.  The approach will draw on behavioral ecology, which views adaptive behavior as responsive to ecological variation.  The speakers, from anthropology and other fields, are known for the depth of their long-term field studies in Kenya, Mali, Bangladesh, the United States, Dominica, Bolivia, the Pacific Islands, and other locales.

Beverly Strassmann, University of Michigan Professor of Anthropology and an affiliate of the Research Center for Group Dynamics at the Institute for Social Research, is the organizer of this Winter series.

This kick-off will be a short presentation to be followed by the RCGD Faculty Meeting. Please note, due to last-minute scheduling conflicts, the originally scheduled 2 pm kick-off reception will not take place.

The series is co-sponsored by the Research Center for Group Dynamics and the Evolution and Human Adaptation Program.

In almost all sexually reproducing organisms (including humans), males and females often deploy conflicting strategies to pass their genes on to the next generation. This is especially true in species where males and females mate with more than one individual. In an evolutionary sense, neither a father nor a mother “cares” as much about the fitness of their partner as they do about the fitness of their offspring. I will discuss the impacts this conflict has on the evolution of genitalia and seminal fluid, with special consideration of humans.

This talk covers our understanding of human evolution through the study of hair and skin phenotypes. Conventional classification approaches have limited our insights into the evolution of hair. The development of cutting-edge high-throughput phenotyping methods is now unveiling the extensive diversity in scalp hair morphology and its genetic underpinnings. By contrasting the progress in skin phenotyping with the untapped prospects in hair research, this presentation will underscore the crucial role of measurement in associating phenotypes with genetic variation and in illuminating the evolutionary history of these human traits.

Maxwell Lemkau is an undergraduate at the University of Michigan interested in behavioral ecology and human behavior who is part of Beverly Strassmann’s lab, using evolutionary theory to study human behavior in the Dogon of Mali.

We investigated religious conversion in the Dogon of Mali, West Africa. The study population has been exposed to Islam and Christianity since the 1940s, and multiple religions (the traditional Dogon religion, Islam, and Christianity) coexist within the same villages and patrilineages. Among these three religions, the Dogon religion and Islam entailed greater participation expenses than did Christianity. Given that a man’s father practiced the traditional Dogon religion, what factors caused him to stay with his father’s religion or to adopt a new religion? Using individual-level data on 570 men from nine villages, we found that men from poorer families were more likely to adopt Christianity, while men from wealthier families chose Islam or stayed with the Dogon religion. We propose that costly expenses of a religious community provide a Dogon man with a group of reciprocators that is well-defined with explicit mechanisms to monitor reputation and avenues through which to promote and enhance his status. The extent that each religion incorporates expenses to achieve these benefits, however, have different tradeoffs to poorer and wealthier individuals.

Culturally transmitted norms have likely structured the selection pressures shaping human behavior and psychology, but focused studies are needed to establish the exact pathways and outcomes of this co-evolutionary process. I present two studies which incorporate our long-standing cultural capacity to develop hypotheses of human behavior in the context of cooperation and conflict. The first study will illustrate how competition between culturally differentiated populations, i.e. cultural group selection, structures the social scale of cooperation in transient interactions with strangers. The second study shows how certain features of combat-related psychological stress can be explained as a psychological adaptation to culturally-structured normative landscapes. Data for these studies were collected in pastoral communities living in northwest Kenya.

Human mothers face an adaptive problem. The importance of maternal care and women’s economic contributions to the household throughout evolutionary history and in contemporary societies requires mothers to decide how to allocate their time and energy between work and childcare in ways that support their reproductive success. In Bangladesh, traditionally boat-dwelling, semi-nomadic Shodagor women engage in two different occupations – trading and fishing – that require different trade-offs between time spent in work and in childcare. In this talk, I will discuss these differences and address three questions: 1) What are the social and cultural predictors of variation in women’s work? 2) What role does environmental change play in structuring women’s economic decisions? And 3) Do differences in trade-offs explain differences in fitness consequences for mothers? Examining variation in women’s strategies for solving the adaptive problem of motherhood provides a better understanding of a critical element of human evolution, and also allows scientists to create models to predict how behavior is likely to change in the future in response to ecological changes (e.g., climate change, local disease ecologies) and to predict the impacts of this on human biology.

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Because human same-sex sexual behavior (SSB) is heritable and leads to fewer offspring, the maintenance of SSB-associated alleles in populations requires an explanation. While several evolutionary genetic hypotheses have been proposed, most lack strong empirical evidence. I will discuss recent UK Biobank-based genomic studies that shed light on this long-standing “Darwinian paradox.”

In times of crisis, risk pooling can enhance the resilience of individuals, households, and communities. Risk pooling systems are most effective when their participants adhere to several principles: (1) participants should agree that the pool is for needs that arise unpredictably, not for routine, predictable needs; (2) giving to those in need should not create an obligation for them to repay; (3) participants should not be not expected to help others until they have taken care of their own needs; (4) participants should have a consensus about what constitutes need; (5) resources should be either naturally visible or made visible to reduce cheating; (6) individuals should be able to decide which partners to accept; and (7) the scale of the network should be large enough to cover the scale of risks. We discuss the cultural and evolutionary foundations of risk pooling systems, their vulnerabilities, and their relationship to commercial insurance.

Charles Darwin posited that social competition among conspecifics could be a powerful selective pressure. Richard Alexander (1989, 1990) proposed a model of human evolution involving a runaway process of social competition based on Darwin’s insight. Here we briefly review Alexander’s logic, and then expand upon his model by elucidating runaway, positive-feedback processes that were likely involved in the evolution of the remarkable combination of adaptations in humans. We discuss how these ideas fit with the hypothesis that increased inter-group interaction and cooperation among individuals in small fission-fusion groups opened the door to runaway social selection and cumulative culture during hominid evolution.

The evolution of human longevity still remains a curious puzzle. Here I provide some new perspectives on the why and how of longevity over the course of human evolution, using longitudinal study of subsistence societies as an imperfect lens for gaining insight. I argue that our evolved human lifespan is about seven decades, and that the multifaceted contributions of middle-to-older aged adults is part of the reason why. I will combine ethnographic, demographic and biomedical studies to shed light on the timing and significance of the transition from “asset” to “burden” in late adulthood, with implications on the global Gray Wave of population aging.