The evolution of human fatigue resistance

Abstract

Humans differ from African great apes in numerous respects, but the chief initial difference setting hominins on their unique evolutionary trajectory was habitual bipedalism. The two most widely supported selective forces for this adaptation are increased efficiency of locomotion and improved ability to feed in upright contexts. By 4 million years ago, hominins had evolved the ability to walk long distances but extreme selection for endurance capabilities likely occurred later in the genus Homo to help them forage, power scavenge and persistence hunt in hot, arid conditions. In this review we explore the hypothesis that to be effective long-distance walkers and especially runners, there would also have been a strong selective benefit among Homo to resist fatigue. Our hypothesis is that since fatigue is an important factor that limits the ability to perform endurance-based activities, fatigue resistance was likely an important target for selection during human evolution for improved endurance capabilities. We review the trade-offs between strength, power, and stamina in apes and Homo and discuss three biological systems that we hypothesize humans evolved adaptations for fatigue resistance: neurological, metabolic and thermoregulatory. We conclude that the evolution of endurance at the cost of strength and power likely also involved the evolution of mechanisms to resist fatigue.

Keywords: Adaptations; Endurance; Homo; Pan; Speed; Trade-offs.

Fig. 1

Schematic of the hypothesis that fatigue resistance was selected in parallel with adaptations for endurance in Homo compared with Pan which is more adapted for strength and power. Adaptions for fatigue resistance were likely precipitated by selection for habitual bipedalism that increased selection for trade-offs in skeletal muscle architecture/physiology, neurological, metabolic, and thermoregulatory functions. H is Homo, PCA is physiological cross sectional area