Tsimane Family Planning Project


My active research is among a population of South American forager-horticulturalists, 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 theirs and their children’s health, growth and development.

This research is facilitated by the Tsimane Health and Life History Project and funded through an NSF DDIG (2010), UCSB Department of Anthropology Summer Research Grants (2011 and 2012), UCSB Spalding Fellowships (2010 and 2011), UCSB Humanities and Social Sciences Research Grant (2010), and UCSB Integrative Anthropological Sciences Donor Grant (2010).

(1) Women's and Men's Fertility Preferences in a Changing Environment

It is generally assumed that small-scale indigenous societies across South and Central America and parts of Africa are disappearing. However, recent demographic surveys suggest these populations have high fertility rates of up to ten children per woman, despite both men and women desiring smaller family sizes. This high fertility, coupled with increasing infant and child survival rates, indicates that these populations will double in size in 14 to 24 years. Most of these societies 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.

I published a paper in the American Journal of Human Biology that tested three hypotheses for why many Tsimane women are having significantly more children than they want. My findings suggest that improved maternal condition (such that women are better able to become pregnant and become pregnant at younger ages), low value to investments in human capital (such that delaying reproduction to invest in education and wage labor is undervalued) and continued reliance on large kin networks for nutritional security and social status are driving factors behind the observed discrepancies between family size preferences and outcomes.

I am preparing two additional papers from this project. The first is in preparation for the Journal of Family Planning and Reproductive Health Care. It examines uptake and maintenance of non-traditional and traditional contraceptive methods in small-scale societies. The second is in preparation for Human Nature. It explores the relationships among market integration, education, perceptions of health and socioeconomic opportunity, and smaller desired family sizes.

(2) Adolescent Pregnancy and Maternal and Infant Growth and Development

My second 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.

The first paper of this project is in preparation for submission to the Proceedings of The National Academy of Sciences, has been presented at the annual meeting of the Human Behavior and Evolution Society and the American Anthropological Association. The paper documents growth patterns in Tsimane women through adolescence, testing for trade-offs in energetic investment between growth and pregnancy. My findings 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 children of mothers aged 15 and younger suffer long-term growth deficits. The second paper from this project will continue to examine the long-term consequences of adolescent reproduction to the growth and health of first born and later born children. The third paper is part of an ongoing collaboration with a colleague at the University of New Mexico at Albuquerque to examine the relationship between age at first birth and maternal and child cognitive development.


To develop these two projects I lived with the Tsimane for six months in 2005. Through participant observation, time allocation, focal follows, age-and-sex stratified focus groups and key informant interviews I used inductive features of grounded theory to begin conceptualizing the issues surrounding fertility and fertility control, as perceived by Tsimane men and women. From this, in 2005, I used semi-structured interviews to assess women’s perceptions of socioeconomic success; and in 2010 and 2011, I used semi-structured interviews with Tsimane and non-Tsimane key informants (e.g. health workers, politicians and teacher) to assess men’s and women’s fertility preferences, and their perceptions of health, nutritional, social and economic security. In addition, my research uses reproductive histories and data on biomarkers of health, growth and somatic maintenance, which were gathered by the Tsimane Health and Life History Project from 2002 to present. For quantitative analyses of this data I use Predictive Analytics Software Statistics version 16.0 (SPSS Inc.) and MAXQDA (VERBI Software) to further my qualitative analyses.


McAllister,L., Gurven, M., Kaplan, H., Steiglitz, J. (2012) Why do women have more children than they want? Understanding differences in women's ideal and actual family size in a natural fertility population. American Journal ofHuman Biology. 24(6):786-99

Related Publications

Veile, A., Martin, M., McAllister, L., Gurven, G. Modernization is Associated with Intensive Breastfeeding in the Bolivian Amazon. Social Science & Medicine. (in press)

Gurven, M., Winking,J., Kaplan, H., von Rueden, C., McAllister,L. (2009) A bioeconomic approach to marriage and the sexual division of labor. Human Nature. 20(2):151-183

Publications in Preparation

McAllister, L., Blackwell A., Garcia, G., Gurven, M. Adolescent Reproduction: A Trajectory or a Tradeoff with Maternal Growth and Health. For submission to Proceedings of The National Academy of Sciences

McAllister L., Gurven, M. Understanding the Failure of Contraceptives in a Small-Scale Society, For submission to Journal of Family Planning and Reproductive Health Care

McAllister L., Gurven, M. How Does Market Integration Reduce Fertility Desires in Marginalized Populations: A Case Study from the Amazon. For submission to Human Nature

Pisor, A., McAllister, L., Gurven, M. Comparing Market Integration and Changes in Fertility Preferences vs. Outcomes in Two Neighboring Small-Scale Societies. For submission to Evolution and Human Behavior

McAllister, L., Blackwell, A., Davis, H., Garcia, G., Gurven, M. The Long-term Consequences of Adolescent Reproduction for First Born and Later Born Children. For submission to Proceedings of the Royal Society B: Biological Sciences