Since 2005, facilitated by the Tsimane Health and Life History Project, I have worked with a population of South American forager-farmers, the Tsimane of Bolivia. This research has two foci: (1) how changing environments affect women’s and men’s fertility preferences and fertility, and consequently women’s reproductive health and autonomy; and (2) how adolescent mothers’ resource allocation — among the competing demands of growth, reproduction and somatic maintenance — affect their and their children’s health, growth and development.

Adolescent Pregnancy and Maternal and Infant Growth and Development

My first project with the Tsimane investigates the effects of early age at first birth and high fertility on maternal growth, health and cognitive development. Women have finite resources. Adolescence is a period of continued growth, and social and cognitive development. Reproducing during adolescence reduces women’s investment in their own growth and somatic maintenance but not completely, such that during gestation and lactation their first-born child receives fewer resources than the first-born children of women who delay their reproduction.

This work explores growth patterns in Tsimane women through adolescence, testing for trade-offs in energetic investment between growth and pregnancy. My findings, to date, support previous research suggesting that early age at first birth stunts maternal growth. However, my findings further suggest that: (1) women who give birth at age 15 or younger continue their growth post-pregnancy (although they are shorter as adults than average); (2) women on faster growth trajectories, do not cease growth earlier and are often taller than average as adults, if their growth is uninterrupted by pregnancy/motherhood; (3) the first-born sons, but not daughters, of mothers aged 15 and younger suffer long-term growth deficits. My future work in this area will investigate the long-term consequences of adolescent reproduction to the growth and health of first born and later born children; and the relationship between age at first birth and maternal and child cognitive development.

Women’s and Men’s Fertility Preference in a Changing Environment

My second project with the Tsimane explores why fertility among the Tsimane remains high (TFR = 9.1) despite small preferred family sizes (IFS = 4 to 5 children), and access to contraceptives and family planning programs. This high fertility, coupled with increasing infant and child survival rates, indicates that the Tsimane population will double in size within 24 years. As the Tsimane are marginalized, face discrimination and have limited land rights, this population growth and the associated environmental degradation are unsustainable. Furthermore, high fertility is associated with negative maternal and child health outcomes and low female autonomy. It is crucial that we better understand the dissonance between these people’s small desired family sizes and fertility, particularly as existing family planning programs and improved access to contraceptives are not having the expected affects.

My research suggests that excess fertility increases with proximity to market towns that provide resource stability and healthcare. Tsimane women living near these urban centers have better maternal condition and likely greater fecundity, which is not countered by increased use of contraceptives. Furthermore, they have low returns on investments in human capital and low socioeconomic mobility: Tsimane women are stuck in their homelands where adult status and success are measured in terms of reproductive status and family size, and sociopolitical power and economic security hinge on large kin networks. Under these conditions, despite a desire for smaller family sizes, women are trapped in a reproductive role, and motivation to delay or reduce reproduction is low. Consequently, adolescent reproduction is the norm for Tsimane women despite trade-offs between maternal and fetal/infant growth, development, cognition and health. However, the evolutionary, sociopolitical and long-term economic advantages (e.g. higher fertility) of an early reproductive start may outweigh these costs. My future work in this area will continue to unravel the interplay between socioeconomic development and evolved life history strategies at the onset of demographic transition.

At Penn State, I have taught one lower-level and one upper-level undergraduate courses. In my Soc 005: Social Problems class, I received an average rating of 6.7/7 from student evaluations. I aimed to guide students through the process of taking in contradictory information and using principles of sociology (i.e. a “sociological imagination”) to form conclusions and their own opinions about society. In my Soc 470: intermediate Social Statistics course, I received an average rating of 6.4/7. My two main goals for this class were to 1) Give students the basics of statistics which they can later build upon if they wish, and 2) Help students evaluate statistics they hear on the news, in media, or otherwise in their everyday life.

Whaling, Sharing, and the Behavioral Ecology of Cooperation

Since 1997 I have spent nearly two years conducting field research in the traditional whaling and sea-hunting village of Lamalera, Indonesia, where I study how cooperative institutions are organized and how cooperatively acquired common-pool natural resources are managed and distributed. A combination of large-prey hunting and high-variance subsistence has made the village an ideal field site for studying cooperative subsistence behavior and human-environment interactions. I am especially interested in how cultural institutions and systems of norms can provide solutions to cooperative dilemmas and the problems posed by collective action. As a human behavioral ecologist, I am also interested in investigating the adaptive mechanisms that underpin human cooperative behavior.

This research relies heavily on social network statistics and modeling to test hypotheses about the organization of cooperative institutions and networks of social support. The results of this research show that several different adaptive mechanisms each explain part of the variation in cooperative behavior and that the underlying hypotheses are not mutually exclusive: kinship, reciprocity, and signaling all play a role in shaping patterns of cooperation and support. However, evolutionary mechanisms do not tell the whole story: social institutions, especially patrilineal kinship, corporate groups, and a complex system of norms governing harvest distributions all contribute to the maintenance of cooperation in this setting. Results from this work can be found in Current Anthropology, Human Nature, and Evolution and Human Behavior.

Evolutionary Demography of Marriage and Reproduction

My demographic research focuses on the ecological factors that influence the onset and timing of reproduction in humans. My recent collaborative work with John Ziker (Anthropology, Boise State) has focused on demographic modeling of the abrupt decline in fertility in his field site of Ust’-Avam in central Siberia following the fall of the USSR. Over a ten-year span the population total fertility rate (TFR) fell from five to one. We were able to show that this precipitous fall in fertility is likely due to a cessation of reproduction in the face of economic and ecological uncertainty following the collapse of the USSR. Results from this collaborative work have recently been published in Human Nature and Sustainability Science.

I use similar methods to investigate marriage delay in Lamalera. This community displays several peculiar demographic features for a subsistence fishing and whaling village, including a very late age of marriage (31 for men and 29 for women), a high rate of female celibacy, and a surprising number of children entering the clergy. This project uses historical demographic methods to analyze these trends in over a century’s worth of church parish records from Lamalera. Borrowing from life history and ecological constraints theory, I relate these demographic trends to the changing socioecology of the village and the effects of household composition and sibling competition on life history outcomes.

Origins and Persistence of Social Inequality in Small-Scale Societies

Since 2007 I have been involved in a Santa Fe Institute initiative studying the origins and persistence of inequality in small-scale societies. Through a series of SFI-hosted workshops, the initial project focused on the role intergenerational transmission of wealth plays in creating and maintaining wealth inequalities. This project pooled together data from 21 different societies (including Lamalera) to examine how wealth inequality was patterned cross-culturally with results published in Science and Current Anthropology. Our Shenk Lab project on marital assortment in small-scale societies, described above, is an extension of this earlier work.