Metabolic Cost of Living in Human Foragers

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Many longstanding hypotheses regarding human ecology and physiology speculate about the energetic demands placed on people in pre-agricultural societies, but energy use in hunter-gatherers has never been measured directly. In this project, daily energy expenditure will be measured for adult men and women of the Hadza, who live in savannah and open woodland habitat in northern Tanzania subsisting on wild foods which they hunt and gather. Energy use data will be compared to activity data and demographic information in order to understand the energetic demands placed on humans in pre-agricultural societies. This study will be the first to measure daily energy expenditure in human hunter-gatherers.Using the doubly-labeled water method, daily energy expenditure (i.e., calories used per day) will be measured over a two-week period. Body mass, fat-free mass, age, and the number and ages of dependents (e.g., children) will be recorded for each subject, as will resting metabolic rate and the energy cost of walking. During the two-week energy measurement period, heart rates and daily activity budgets, including the distance walked each day, and the time spent foraging and resting, will also be recorded for each subject,. Together, these data will be used to establish the daily energy budget for human foragers, as well as the proportion of the daily energy budget spent on various activities including resting metabolism and travel. Daily energy budgets will then be compared among subjects to determine the effects of gender, age, and number of dependents on daily energy expenditure. These data will be used to test and inform hypotheses regarding the energetic and physiological demands on humans in pre-agricultural societies. A graduate student and two Tanzanian researcher assistants will earn important research experience through their involvement with this project. Results will be incorporated into the curriculum at Washington University.