Health costs of reproduction are minimal despite high fertility, mortality and subsistence lifestyle

Abstract

Women exhibit greater morbidity than men despite higher life expectancy. An evolutionary life history framework predicts that energy invested in reproduction trades-off against investments in maintenance and survival. Direct costs of reproduction may therefore contribute to higher morbidity, especially for women given their greater direct energetic contributions to reproduction. We explore multiple indicators of somatic condition among Tsimane forager-horticulturalist women (Total Fertility Rate = 9.1; n = 592 aged 15-44 years, n = 277 aged 45+). We test whether cumulative live births and the pace of reproduction are associated with nutritional status and immune function using longitudinal data spanning 10 years. Higher parity and faster reproductive pace are associated with lower nutritional status (indicated by weight, body mass index, body fat) in a cross-section, but longitudinal analyses show improvements in women's nutritional status with age. Biomarkers of immune function and anemia vary little with parity or pace of reproduction. Our findings demonstrate that even under energy-limited and infectious conditions, women are buffered from the potential depleting effects of rapid reproduction and compound offspring dependency characteristic of human life histories.

Figure 1. Longitudinal trajectories of weight among women age 15+.

Women with (a) sustained weight decline, or oscillations with mean decrease >0.3 standard deviations (SD); (b) sustained weight gain, or oscillations with mean increase >0.3 SD; (c) oscillations with mean increase or decrease <0.3 SD.

Figure 2. Effects of parity and inter-birth interval on women’s nutritional status for women aged 15–44.

Panels include (a) weight, (b) body fat percentage, and (c) BMI. Interbirth interval (IBI) defined as the mean ± 1 SD (2.50 ± 0.83 years). Solid lines convey predicted marginal effect of parity and IBI, holding all other variables at sample averages, including age. Dashed lines use average age at first birth for parity = 1, and then add the IBI to each age in the regression models given in Table 3. Average age at first and last birth is 18 and 38, respectively.