I am interested in understanding human social behavior in terms of microbial transmission. Along with Dr. Athena Aktipis, I co-direct a multi-disciplinary Microbiome & Behavior Project, housed in the Department of Psychology at Arizona State University.
Transmission and the Nature of Symbioses
The human body is a microbial habitat. Our behavior is affected and affects the nature of the relationship between host and its microbiota. Selection operates at the level of the individual host, and, at a much more rapid pace, within microbial strains resident within the body during each human generation. Transmission processes are central to understanding the nature of symbioses. Vertical transmission of microbes, from parent to offspring, generates selection pressures on microbes that parallel those operating on the host: mutations with deleterious effects on host fitness should be selected against. In contrast, independent transmission opportunities decouple fitness interests of microbial straints with the current host, and may lead to the evolution of virulence.
Sociality and Microbial Transmission
The risk of pathogen exposure from host social interaction is an accepted cost of sociality, and hypothesized behavioral mechanisms to reduce these costs, such as disgust. Yet, there is little existing research to understand behavioral mechanisms that might have been designed to enable the replenishment of beneficial digestive microbiota.
The goal of my next set of projects is to understand cross-cultural food sharing practices and dietary patterns in terms of microbial transmission. The practice of taking food from a common plate could be particularly important for maintaining a stable pool of common microbial species in a population, adapted for a particular ecology and diet. Common-plate meals should be associated more frequently with plant-based diets than they are with other dietary regimes, as humans require microbes from other individuals to degrade plant polysaccharides. We are currently (Jan 2017-July 2017) collecting samples from homes in the Human Generosity Project field sites to test these ideas.
Old Friends / Hygiene Hypothesis
I am also interested in understanding the health impacts of the microbiome of the built environment during development. All the species resident in the adult human microbiota must be acquired through horizontal transmission during the first several years of life, and microbial exposure is thought to be essential for training the adaptive immune system to respond appropriately to antigens during later life. The increasing prevalence of inflammatory conditions in Westernized, developed countries has been argued to be the result of lack of exposure to plant and animal-derived microorganisms that would have been ubiquitous during our species’ evolutionary history.
A second theme of my work at ASU investigates the possibility of microbial involvement in pathologic eating conditions. Investigation of microbial involvement in understanding the global health problem of obesity is a central focus for this work. Evolutionary explanations for the rise in obesity have focused on identifying the genetic or developmental adaptations that responded to food scarcity over human evolution by increasing the body’s ability to store energy reserves in the form of adipose tissue. However, the uneven distribution of obesity, both within and between populations living in similarly obesogenic environments, suggests that a primary causal factor, overeating, is not an obligate response to an overabundance of palatable food.
Gut microbiota have access to the pathways of chemical communication between the gut and brain, a concept referred to as the gut-brain-microbiota axis, and therefore could potentially alter host behavior to suit their own interests. Our initial study on microbial involvement in overeating behavior tested the hypothesis that sugar-degrading oral bacteria could influence their hosts to consume sugar. In this study, we used metagenomics methods to determine the abundance of sugar-degrading bacteria in the oral cavity, and assessed sugar consumption with dietary questionnaires and ad-libitum access to a sugary food during a lab visit. I presented these results at the annual meetings of the Human Behavior & Evolution Society and Society for Evolutionary Medicine and Public Health, and data analysis efforts are ongoing.
Resource Sharing & Risk Buffering
My work within the Human Generosity Project focuses on understanding social relationships and sharing in the context of
resource scarcity. I am currently finishing up data collection for a lab-based study of resource sharing, comparing the levels of allocation given subtle priming cues for concepts associated with various social relationships (e.g., friendship). We are currently in the planning stages of extending this work in a materially disadvantaged population living in the U.S. This work will focus on understanding social coping strategies in the context of chronic poverty and environmental risk.