Life History Transitions Among the Toba

Life History Transitions Study
Funded by the National Science Foundation, NSF BCS-0952264, a CAREER Award to Claudia Valeggia

Principal Investigator: Claudia Valeggia, PhD, Yale University, USA
Co-PI: Melanie Martin, PhD – U of Washington, USA

 The C.A.R.E. project is in the early stages of a five year longitudinal study to examine the somatic, developmental, cultural, and endocrine correlates of three life history transitions among the Toba of Namqom. In addition to three, distinct studies focused on infancy-childhood, puberty, and menopause, the team continues to collect village-wide anthropometric and life history event data annually for five years. Combined with similar data collected since 1997, the project will be able to test life history theory and reproductive ecology hypotheses related to the trade-offs underlying key human life history events.

This study examines the following life-history transitions:

The Weaning Period:

This section of the project aims to explore the transition from birth to complete weaning. The transition between infancy and childhood involves an important energetic trade-off.  The infant starts relying increasingly less on breastmilk and more on other types of food, which implies a change in food processing metabolism and immune function (Dettwyler, 2004). This is accompanied by well defined changes in growth patterns.

We will use data on children’s growth trajectories, development, nutrition, and health to follow Toba newborns through the weaning transition.

The Pubertal Transition

Puberty, a milestone in development in sexually reproducing organisms, can be interpreted as the transition in energy allocation from somatic growth to reproductive function. The timing and tempo of this transition exemplifies the classic life history trade-off known as the cost of reproduction, or current vs. future reproduction. In women, an early age at first reproduction may extend their reproductive life, but it compromises the health of both mother and infant (Fraser et al., 1995). On the other hand, delaying reproductive maturity decreases lifetime reproductive opportunity. A reflection of the adaptive consequences of this trade-offs is dramatic variation across human populations in the timing of puberty.

We will characterize the pubertal transition in girls by analyzing data on growth, maturation, health, and hormonal changes in the years up to and through menarche, the visible event that marks the transition to reproductive life.

The Menopause Transition

Menopause, or the cessation of menstrual periods, is a universal event for women; however, the frequency, prevalence and intensity of the physical discomforts associated with the end of reproductive functioning do not seem to be as consistent. This phase of the project is a continuation of early work started in NamQom to assess the hormonal, cultural and physiological correlates of the menopause transition.

We will characterize the menopausal transition by analyzing data on anthropometric, health, and hormonal changes at the end of women’s reproductive life.