The thermoregulatory advantages of hominid bipedalism in open equatorial environments: the contribution of increased convective heat loss and cutaneous evaporative cooling

Wheeler, P.E.

doi:10.1016/0047-2484(91)90002-d

Cited by 139 publications

(80 citation statements)

References 6 publications

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“…Such results support the use of savanna chimpanzees as models for understanding adaptation to marginal environments, such as that which has been proposed during the expansion of hominins into savanna habitat from forested habitat (Reed, 1997;Bobe and Behrensmeyer, 2004;White et al, 2009;Copeland et al, 2011), and therefore likewise the significance of savannas within the hominin ecological niche (Quinn et al, 2013). These results further underline the uniqueness of thermoregulatory stress to individuals in savanna environments, thereby supporting established theory that thermoregulation was a novel and necessary evolutionary hurdle to be overcome in the expansion of hominins into similar environments (Wheeler, 1984(Wheeler, , 1991, and supporting their use as models for understanding the mechanisms involved in early hominin adaptations to thermoregulation.…”

Section: Discussionsupporting

confidence: 67%

Seasonal Variation in Physiology Challenges the Notion of Chimpanzees (Pan troglodytes verus) as a Forest-Adapted Species

et al. 2018

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Section: Discussionsupporting

confidence: 67%

Seasonal Variation in Physiology Challenges the Notion of Chimpanzees (Pan troglodytes verus) as a Forest-Adapted Species

et al. 2018

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“…However, our model also suggests that if bipedality evolved for other reasons, then there would have been no thermoregulatory opposition to this adaptation. Our predictions stand in contrast to those of Wheeler (3,8,9), who demonstrated that (for an individual standing at rest) bipedalism reduces external heat load and thus would have reduced thermal challenge. The key difference is that for our model (of an exercising individual), external heat challenge is much less important than internally generated heat, and so the effect described by Wheeler makes a trivial difference to heat balance.…”

Section: Discussioncontrasting

confidence: 54%

“…One line of reasoning posits that thermoregulation may have been important in the evolutionary development of both of these traits. Highly supportive of such discussions has been a series of papers by Wheeler that used simple heat-balance models to quantify the potential effects of such adaptations (3)(4)(5)(6)(7)(8)(9)(10). Recently, we presented a revised version of Wheeler's model to explore thermoregulatory aspects of putative endurance running in extinct hominids (11).…”

mentioning

confidence: 99%

Avoidance of overheating and selection for both hair loss and bipedality in hominins

Ruxton

Wilkinson

2011

Proc. Natl. Acad. Sci. U.S.A.

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Two frequently debated aspects of hominin evolution are the development of upright bipedal stance and reduction in body hair. It has long been argued, on the basis of heat-balance models, that thermoregulation might have been important in the evolution of both of these traits. Previous models were based on a stationary individual standing in direct sunlight; here we extend this approach to consider a walking hominin, having argued that walking is more thermally challenging than remaining still. Further, stationary activities may be more compatible with shade seeking than activities (such as foraging) involving travel across the landscape. Our model predictions suggest that upright stance probably evolved for nonthermoregulatory reasons. However, the thermoregulatory explanation for hair loss was supported. Specifically, we postulate progressive hair loss being selected and this allowing individuals to be active in hot, open environments initially around dusk and dawn without overheating. Then, as our ancestors' hair loss increased and sweating ability improved over evolutionary time, the fraction of the day when they could remain active in such environments extended. Our model suggests that only when hair loss and sweating ability reach near-modern human levels could hominins have been active in the heat of the day in hot, open environments.T wo frequently debated aspects of hominin evolution are the development of upright stance and the reduction in body hair. Indeed, a good case can be made that upright stance was "the first novelty of our lineage" (1), and lack of hair is one of the visually most obvious aspects of modern humans compared with other similar-sized mammals (2). One line of reasoning posits that thermoregulation may have been important in the evolutionary development of both of these traits. Highly supportive of such discussions has been a series of papers by Wheeler that used simple heat-balance models to quantify the potential effects of such adaptations (3-10). Recently, we presented a revised version of Wheeler's model to explore thermoregulatory aspects of putative endurance running in extinct hominids (11). The key modification in our revised model was a change from a stationary individual, as considered by Wheeler, to a moving one. Movement both adds to the thermal challenge on an individual by increasing their metabolically generated heat production and allows greater heat loss to the air by forced convection. Here we apply a further development of this model to the issues in which Wheeler was originally interested: bipedalism and hair loss.We believe that consideration of a walking individual should be particularly informative, because it is easier to envisage ecological reasons why an individual would be required to walk through areas that offer no shade compared with situations where an individual would stand still for long periods in direct sunlight. Vision is likely to have been an important sense in both food finding (e.g., searching for and pursuing mobile animal prey) and predator...

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“…This temperature record is relevant to the evolutionary origin or maintenance of a unique suite of adaptations that permit humans to remain active under high ambient heat loads. For example, upright posture in hot, open environments confers thermophysiological advantages to bipedal hominins owing to reduced interception of direct solar radiation and to displacement of the body away from the nearsurface environment, which may be excessively hot due to solar heating (29). Derived human traits such as very little body hair, high sweating capacity, and high surface area to volume ratio are also advantageous for daytime activity in hot, arid climates (30), and temperature is a central variable in hypotheses of behaviors such as long-distance scavenging and persistence hunting (31).…”

Section: Resultsmentioning

confidence: 99%

High-temperature environments of human evolution in East Africa based on bond ordering in paleosol carbonates

Passey

Levin

Cerling

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

382

364

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Many important hominid-bearing fossil localities in East Africa are in regions that are extremely hot and dry. Although humans are well adapted to such conditions, it has been inferred that East African environments were cooler or more wooded during the Pliocene and Pleistocene when this region was a central stage of human evolution. Here we show that the Turkana Basin, Kenya—today one of the hottest places on Earth—has been continually hot during the past 4 million years. The distribution of 13 C- 18 O bonds in paleosol carbonates indicates that soil temperatures during periods of carbonate formation were typically above 30 °C and often in excess of 35 °C. Similar soil temperatures are observed today in the Turkana Basin and reflect high air temperatures combined with solar heating of the soil surface. These results are specific to periods of soil carbonate formation, and we suggest that such periods composed a large fraction of integrated time in the Turkana Basin. If correct, this interpretation has implications for human thermophysiology and implies a long-standing human association with marginal environments.

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The thermoregulatory advantages of hominid bipedalism in open equatorial environments: the contribution of increased convective heat loss and cutaneous evaporative cooling

Cited by 139 publications

References 6 publications

Seasonal Variation in Physiology Challenges the Notion of Chimpanzees (Pan troglodytes verus) as a Forest-Adapted Species

Seasonal Variation in Physiology Challenges the Notion of Chimpanzees (Pan troglodytes verus) as a Forest-Adapted Species

Avoidance of overheating and selection for both hair loss and bipedality in hominins

High-temperature environments of human evolution in East Africa based on bond ordering in paleosol carbonates

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