Horticultural activity predicts later localized limb status in a contemporary pre‐industrial population

Abstract

Objectives Modern humans may have gracile skeletons due to low physical activity levels and mechanical loading. Tests using prehistoric skeletons are limited by the inability to assess behaviour directly, while modern industrialized societies possess few socio-ecological features typical of human evolutionary history. Among Tsimane forager-horticulturalists, we test whether greater activity levels and, thus, increased loading earlier in life are associated with greater later-life bone status and diminished age-related bone loss. Materials and Methods We used quantitative ultrasonography to assess radial and tibial status among adults aged 20+ years (mean±SD age=49±15; 52% female). We conducted systematic behavioural observations to assess earlier-life activity patterns (mean time lag between behavioural observation and ultrasound=12 years). For a subset of participants, physical activity was again measured later in life, via accelerometry, to determine whether earlier-life time use is associated with later-life activity levels. Anthropometric and demographic data were collected during medical exams. Results Structural decline with age is reduced for the tibia (female: -0.25 SDs/decade; male: 0.05 SDs/decade) versus radius (female: -0.56 SDs/decade; male: -0.20 SDs/decade), which is expected if greater loading mitigates bone loss. Time allocation to horticulture, but not hunting, positively predicts later-life radial status (βHorticulture=0.48, p=0.01), whereas tibial status is not significantly predicted by subsistence or sedentary leisure participation. Discussion Patterns of activity- and age-related change in bone status indicate localized osteogenic responses to loading, and are generally consistent with the logic of bone functional adaptation. Non-mechanical factors related to subsistence lifestyle moderate the association between activity patterns and bone structure.

The Exposome in Human Evolution: From Dust to Diesel

“…This combination suggests energetic tradeoffs in maintenance of skeletal tissues in higher pathogen contexts. Extant horticultural populations with high parasite and pathogen loads and high total fertility rates tend to have low bone mass density (Stieglitz et al 2015(Stieglitz et al , 2017(Stieglitz et al , 2019, and shorter stature (Blackwell et al 2017;Urlacher et al 2018). These tradeoffs are consistent with the recent increase of European adult height in association with reduced early infections, and are discussed below.…”

Complex variation of trabecular bone structure in the proximal humerus and femur of five modern human populations

“…reproduction), has significant bearing on understanding the evolution of human skeletal phenotype (Gordon, 2013;Pontzer, 2012;Stieglitz, Trumble, Kaplan, & Gurven, 2017;Stock, 2006;). Understanding the extent of human bone structural variation and how factors such as activity, diet, climate, disease load, and genetics influence bone structure also has important implications for understanding the increasing prevalence of complications stemming from agerelated bone loss in a clinical setting (Burge et al, 2007;Weaver et al, 2016;Wright et al, 2014).…”

Bioarchaeology in perspective: From classifications of the dead to conditions of the living

“…The case remains, however, that without being able to observe behavior directly, the record for skeletal robusticity and its relationship to mechanical demand, including mobility, are limited. In this regard, newly emerging human experimental and bioethnographic evidence reveals important findings that are consistent with the bioarchaeological record regarding mobility and behavioral regimes (e.g., Shaw & Stock, , ; Stieglitz, Trumble, Kaplan, & Gurven, ). Moreover, the developmental changes, including bone mass and robusticity in earlier life are maintained in later life well after the loading regime ceases (e.g., Warden et al, ).…”