The study of comparative energetics offers a valuable way to identify broad ecological principles and assess the functional significance of energetic adaptations during the course of evolution. Yet, the quantification of energetic status for nonhuman primates under natural conditions remains one of the most challenging aspects of comparative energetics research. Here, we report on the development of a noninvasive field method for measuring energetic status in great apes, humans, and possibly other nonhuman primates. Specifically, we have explored measurement of a urinary metabolite of insulin (C-peptide) as a physiological marker of energetic condition in chimpanzees and orangutans. We performed three validation studies and successfully measured C-peptide in urine samples from captive chimpanzees, wild chimpanzees, and wild orangutans. Urinary C-peptide measures gave indications of being a reliable signal of energetic status in both species. For chimpanzees and orangutans in the wild, baseline urinary C-peptide levels were higher during periods of fruit abundance than periods of low fruit availability. Urinary C-peptide levels were also higher for well-fed captive chimpanzees compared with wild chimpanzees. Although sample size was small, top-ranking male chimpanzees showed higher C-peptide levels in the wild than low-ranking males only during the period of fruit abundance. These preliminary results indicate that further development of the urinary C-peptide method could expand opportunities to quantify energetic condition for great apes in the wild and generate new data for comparative research. We highlight specific applications for studying great ape reproduction as well as the nutritional ecology of human foragers.

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We analyzed body mass index (BMI = wt/height(2)) and percent body fat (BF%) in adults of the Hadza, an egalitarian society with a strong food-sharing ethic, to examine variation in energetic status in relation to sex, age, and time of year. Data collected from 26 camps over six field seasons gave a cross-sectional sample of 238 males and 235 females and a small longitudinal sample (n = 54). We found that mean BMI showed no sex difference [20.1 +/- 1.6 (SD) kg/m(2) for males and 20.3 +/- 2.2 kg/m(2) for females] and remained similar, regardless of age or time of year. Mean BF% showed a significant sex difference, as expected [10.6 +/- 3.2 (SD) % for males and 19.0 +/- 7.0% for females (P < 0.0001)], with two significant age departures from uniformity: (1) males in the prime age group (30-45 years, n = 79) had a higher mean BF% (11.7%) compared to other ages (P < 0.03), and (2) females in the extreme elderly age group (> 75 years, n = 11) had a lower mean BF% (11.3%) compared to other ages (P < 0.004). In the longitudinal sample, we found no significant change over time in mean BMI or BF%. However, relative change in BF% fluctuated within individuals by as much as 20% of initial values for both sexes. Taken collectively, our results support the idea of broad nutritional homogeneity among the Hadza, but indicate that subtle, potentially important differences in energetic condition exist as well.

Background: Embedded in the emerging area of evolutionary medicine is the premise that evolutionary biology can serve a pedagogical function with widespread applications for education and outreach. Although great strides have been taken over the decades by the science education community to improve evolution education in general, the knowledge gulf or gap between advances in evolutionary medicine and public understanding through the educational system has widened at a rapid pace-and not without consequences for public health, especially for young people. Epidemiological data indicate that the high rates of obesity and type-2 diabetes have begun to extend to adolescents and teenagers, an alarming trend of great concern. Would knowledge of the evolutionary biology perspective on diet and health have value for young people? Little is known about the efficacy of evolutionary medicine education as a public health outreach strategy. A small study was conducted at a New England high school and consisted of two research components: (1) a cross-sectional survey of students' views about what "healthy eating" means and (2) an intervention experiment designed to isolate exposure to knowledge of evolutionary biology. Data were collected through the use of questionnaires and analyzed according to qualitative methods. Results: The survey results showed that students had an accurate view of general guidelines for healthy eating in alignment with public health messaging (e.g., avoiding junk food, eating lots of fruits and vegetables). The main result from the intervention experiment showed that students who received instruction in nutritional physiology alone did not change their view of what "healthy eating" means, whereas students who received instruction in nutritional physiology coupled with evolutionary biology changed their views of healthy food choices, leading to intended dietary changes. Conclusions: A brief, one-time exposure to key concepts in evolutionary biology brought about a shift in students' perceptions of healthy eating. An approach that can cause a shift in perception or attitude, considered an essential first step toward effecting behavioral change, merits further attention and development. Evolutionary medicine education holds strong potential as an untapped yet effective public health outreach strategy regarding the dietary choices of youth.

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