Productivity loss associated with functional disability in a contemporary small-scale subsistence population.

Jonathan Stieglitz,Michael D Gurven,Benjamin C Trumble,Paul L Hooper,Hillard Kaplan

doi:10.7554/elife.62883

Abstract

In comparative cross-species perspective, humans experience unique physical impairments with potentially large consequences. Quantifying the burden of impairment in subsistence populations is critical for understanding selection pressures underlying strategies that minimize risk of production deficits. We examine among forager-horticulturalists whether compromised bone strength (indicated by fracture and lower bone mineral density, BMD) is associated with subsistence task cessation. We also estimate the magnitude of productivity losses associated with compromised bone strength. Fracture is associated with cessation of hunting, tree chopping, and walking long distances, but not tool manufacture. Age-specific productivity losses from hunting cessation associated with fracture and lower BMD are substantial: ~397 lost kcals/day, with expected future losses of up to 1.9 million kcals (22% of expected production). Productivity loss is thus substantial for high strength and endurance tasks. Determining the extent to which impairment obstructs productivity in contemporary subsistence populations improves our ability to infer past consequences of impairment.

Highlights

As the longest living and slowest growing primate, humans experience unique physical impairments with potentially large economic and social consequences
Neither men’s age nor thoracic vertebral body bone mineral density (BMD) is significantly associated with fracture risk (Figure 2), regardless of fracture grade
In comparative cross-species perspective, modern human life histories are characterized by delayed peak foraging efficiency (e.g. Kaplan, 1994; Kaplan, 1997; Koster et al, 2020; Walker et al, 2002), complex cooperative strategies to produce and rear altricial, slow-growing offspring (e.g. Hawkes, 2003; Kaplan et al, 1985; Richerson and Boyd, 2008; Wood and Marlowe, 2013), low adult mortality rate (e.g. Hill et al, 2001; Wood et al, 2017), and long post-reproductive lifespan (e.g. Gurven and Kaplan, 2007; Hawkes et al, 1998; Kaplan et al, 2010)

Summary

Introduction

As the longest living and slowest growing primate, humans experience unique physical impairments with potentially large economic and social consequences. Functional disability of degenerative origin may hinder hominin foraging in costly ways These costs amplify if disability hinders resource transfers or provisioning of other assistance, given their potential fitness impacts (Gurven et al, 2012; Hawkes, 2003; Hill and Hurtado, 2009; Hooper et al, 2015; Marlowe, 2003; Schniter et al, 2018; Wood and Marlowe, 2013). The ubiquity among hunter-gatherers to form social groups of clusters of multi-generational resource-pooling units (Kaplan et al, 2009; Migliano et al, 2017), and in base camps at least ~400 kya

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