Culture, Killing, and PTSD with Sarah Mathew

Hosts Dave Pietraszewski and David Pinsof introduce guest Sarah Matthew, a professor at Arizona State University. The discussion explores the unique interdisciplinary environment of ASU's School of Human Evolution and Social Change, highlighting how institutional structures encourage freedom and collaboration across diverse fields without rigid departmental constraints.

Sarah Matthew discusses specific interdisciplinary projects enabled by her academic environment, including combining cultural evolutionary approaches with genetic population structures among the Turkana. She also describes collaborating with legal scholars on normativity and artificial intelligence, showcasing how flexible institutional settings foster innovative cross-disciplinary partnerships.

Host Dave Pietraszewski and guest Sarah Mathew discuss anthropological fieldwork among the Turkana people, examining how they consume meat from animals dying of disease without getting sick. They explore whether this resilience stems from cultural knowledge or physiological adaptations, highlighting pastoralist practices and the importance of social learning in human survival across harsh environments.

The hosts and Sarah Mathew continue their discussion by considering thought experiments about human survival in unfamiliar environments. They reflect on whether individual reasoning alone is sufficient to thrive in extreme habitats like deserts or the Arctic, concluding that accumulated cultural transmission is essential rather than relying on innate personal capability.

Sarah Mathew, Dave Pietraszewski, and David Pinsof discuss evolved psychological predispositions for social learning, contrasting older models with modern perspectives from artificial intelligence and cognitive science on how mental structures and modularity develop with minimal genetic priors.

The speakers distinguish between a highly modular phenotypic outcome and the minimalistic genetic and developmental processes that produce it, connecting these ideas to debates in developmental psychology and Sarah Mathew's entry into the field of cultural evolution.

Guest Sarah Mathew discusses with hosts Dave Pietraszewski and David Pinsof her transition from studying ants to human evolutionary biology. Inspired by cultural evolution frameworks, she highlights how human cooperation stands out in the animal kingdom, noting its immense scale, flexibility, and intensity at both large and small scales compared to other social species.

Sarah Mathew illustrates small-scale human cooperation using field observations from Turkana, where individuals maintain distant friendships and mutual investments. The speakers explore the paradox of humans achieving massive cooperative feats while remaining largely self-interested, contrasting human egalitarian norms with insect eusociality and hierarchical animal systems.

Host Dave Pietraszewski, David Pinsof, and guest Sarah Mathew discuss human cooperation, contrasting it with other species through human reliance on culture and imitation. Mathew explains group structured cultural selection, detailing a genetic and cultural study of pastoral groups in Northwest Kenya, which revealed low genetic variation between groups but significantly higher cultural variation.

Sarah Mathew and the hosts explore how cultural group selection shapes norms around raiding and cooperation among the Turkana people in Kenya. They discuss how norms establish in-group boundaries across a large population while intergroup warfare persists due to classic collective action problems and the breakdown of cooperation across ethnic borders.

Dave Pietraszewski, David Pinsof, and Sarah Mathew discuss how social norms serve as coordination solutions that manage common knowledge and allow humans to achieve high levels of cooperation despite being fundamentally self-interested. They examine cultural group selection, ecological resource extraction, and how normative packages spread through competition.

The hosts and guest explore whether human tribalism and intergroup animosity should be viewed as cultural adaptations rather than purely genetic ones. They discuss how cultural practices that extract resources and defend groups proliferate, while noting that gene-culture coevolution remains an empirical question.

Dave Pietraszewski, David Pinsof, and Sarah Mathew discuss how cultural norms interact with evolved human psychology during intergroup conflicts. They explore whether humans are predisposed to learn specific tribal norms, how cultural packages leverage partner-choice psychology to demonize outgroups, and empirical findings on ethnic essentialism among the Turkana and Toposa groups.

The speakers transition to discussing a study on post-traumatic stress disorder among Turkana warriors conducted with Matt Zefferman. Sarah Mathew shares her initial ethnographic observations, noting that warriors did not spontaneously report symptoms like intrusive thoughts, prompting an evolutionary behavioral science inquiry into trauma, physical danger, and norm psychology.

Sarah Mathew discusses how PTSD symptoms split into universal physical danger responses, such as hypervigilance and startle seen cross-culturally in groups like the Turkana, and depressive symptoms linked to motivational changes. The speakers explore how navigating complex social norms and moral violations during war shapes these motivational and psychological outcomes.

Sarah Mathew and the hosts examine differences in depressive symptom severity between US soldiers and Turkana warriors, connecting them to moral violations and social sanctions. They conclude that the elaborate cultural norms and rituals surrounding warfare highlight the crucial role of cultural adaptation alongside evolved human psychology.

Dave Pietraszewski, David Pinsof, and Sarah Mathew discuss how norms govern warfare and how genetically evolved psychological mechanisms make humans vigilant about norm violations. They examine the various moral events and violations experienced by the Turkana, such as abandoning injured comrades, failing to share resources, or facing blame from families when a companion dies on a raid, and how these relate to depressive symptoms.

The hosts and Sarah Mathew explore whether individuals anticipate social disapproval or rely on community reactions as a moral compass. Mathew shares surprising findings regarding combat killing among the Turkana: despite strong cultural institutions and permanent bodily scar markers rewarding warriors, individuals who killed in combat reported higher depressive symptom severity and experiences of feeling haunted.

The speakers discuss the psychological challenges and moral violations of killing in warfare, examining how cultural mechanisms and institutions help groups overcome a natural aversion to violence. They contrast different cultural approaches to conflict, such as those of the Turkana versus modern nation-states, and consider how changing institutional rules and incentives might reduce war and intergroup hostility.

As the episode concludes, the hosts thank guest Sarah Mathew for her invaluable empirical and theoretical fieldwork with the Turkana. They reflect on broader paradigm shifts regarding human nature, discussing how social norms, fairness, and egalitarianism operate as sophisticated mechanisms for coordinating self-interest and maintaining cooperative groups.

Hosts Dave Pietraszewski and David Pinsof wrap up the episode by encouraging listeners to share positive feedback on social media, email suggestions for future episode ideas and guests, and humorously reflect on the podcast's impact.

In the final moments of the excerpt, the hosts joke about saving lives through their podcast episodes before officially saying goodbye to the audience until next week.