More specifically, we hypothesize that there was selection for adaptations to resist fatigue, but also that some adaptations for endurance also help resist fatigue. Here we explore the hypothesis that for the genus Homo to be effective long-distance walkers and runners there would also have been a strong selective benefit to resist fatigue. Digging is another sustained physical activity that hunter-gatherer women often do for many hours a day (Marlowe 2010 Kraft et al. Persistence hunts by modern hunter-gatherers typically involve a combination of walking and slow running over 15–30 km (Liebenberg 2006 Lieberman et al. erectus, hominins were also selected for the ability to run long distances to scavenge and persistence hunt in hot, arid conditions (Bramble and Lieberman 2004 Lieberman and Bramble 2007). When walking, hunter-gatherers often carry substantial loads including children and food. erectus hunter-gatherers probably walked similar distances as modern hunter-gatherers in tropical habitats, who average 9–15 km/day (Marlowe 2005). 2009).įurther selection for endurance capabilities likely occurred during the evolution of the genus Homo.
Short daily travel distances reduce energetic costs although transport costs in chimpanzees, measured as volume of muscle activated per meter, are approximately two times higher than in humans (Pontzer et al. Chimps walk on average 2–4 km/day (Pontzer and Wrangham 2004) and gorillas typically travel less than 1 km/day (Goldsmith 1999). Although daily travel distances for australopiths are unknown, they likely walked farther per day than extant African great apes. The ability to walk long distances efficiently likely helped australopiths forage for widely dispersed resources, such as underground storage organs (Laden and Wrangham 2005) and perhaps also avoid predation from predators during periods of peak midday heat (Lieberman 2015). Regardless of the initial driving forces selecting for bipedalism between 6 and 9 million years ago, hominins belonging to the genus Australopithecus between 3 and 4 million years ago were inhabiting relatively open habitats and were capable of striding walking gaits with relatively extended hips and knees (Ward 2002 Raichlen et al. 2009) and improved ability to feed in upright contexts (Hunt 1994 Thorpe et al. Among the many proposed selective forces thought to have favored the origin of habitual bipedalism, the two most widely supported by paleontological and experimental data are increased efficiency of locomotion (Rodman and McHenry 1980 Sockol et al. How and why habitual bipedal posture and locomotion evolved in hominins is the subject of intense debate. 2005 Richmond and Jungers 2008 Lovejoy et al. We conclude that the evolution of endurance at the cost of strength and power likely also involved the evolution of mechanisms to resist fatigue.Īlthough humans differ from other mammals in numerous respects, the fossil record supports Darwin’s 1871 speculation that a chief initial difference that set the human lineage on a separate evolutionary path from the apes was habitual bipedalism (Zollikofer et al. 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. 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. 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. 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. The two most widely supported selective forces for this adaptation are increased efficiency of locomotion and improved ability to feed in upright contexts. Humans differ from African great apes in numerous respects, but the chief initial difference setting hominins on their unique evolutionary trajectory was habitual bipedalism.
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