Analysis of Endurance Running (ER) hypothesis and the evolution of Homo Genus amidst Criticisms

The Endurance Running (ER) hypothesis as proposed by Bramble & Lieberman (2004) is one of the recent anthropological paradigms collectively labeled as ‘open plain’ hypotheses (Dart 1925). The idea started that early humans left the forests and adapted to living on open environment that account for our evolution. Although this hypothesis has gathered criticism (Pickering & Bunn 2007), yet paradoxically enough it remains the dominant accepted paradigm in today’s human evolution documentaries seen in BBC. Succinctly, the hypothesis that humans evolved as endurance runners is perpetuated by physiological and anatomical traits. Unfortunately, it did nothing to answer the biological riddle: what advantage would ER have been to homo genus? In an evolutionary game of roulette, where the struggle is to eat or be eaten – speed, and not endurance, should be a self-efficacy trait as being able to run for hours to hunt makes no sense from an evolutionary viewpoint. This essay will examine the ER hypothesis, that while homo genus were competent enough to pursue prey, but to think that natural selection redesigned our simian form to endure long distance running and the suggestion that humans shifted to drier habitats away from water are ludicrous.

Bramble & Lieberman (2004) cited twenty derived anatomatical characteristics that claimed to be adaptations for efficient ER. Aiello & Dean (1990) discovered that some of these evidently cursorials distinct traits existed first in the fossil records of H.Habilis, others developed initially in H.erectus and then in H.Sapiens, signifying a much more complex story than proposed. The list of theoretically derived anatomical features with their own cursorial functions seems to be flawed due to the fact that the assumption was deduced without substantial systematic comparisons with other animals but was merely restricted to hominids and pans fossils. A more holistic statistic evaluation would have been more reliable as convergent traits are strong indicators of evolution in similar environments (Losos 2011). In addition, deliberations of possible locomotion styles is restricted to merely walking and running with no contemplation at all given to aquatic activities, yet we are more accomplished swimmers and divers than other primates (Pilbeam et al 2005). The need to include the ‘waterside model’ in the evolution of homo genus through ER is important as palaeoecological evidence associated with Homo fossil and archaeological sites strongly suggests that Homo may well have been a waterside dweller (Pilbeam et al 2005). Most of the anatomical features said to be for walking could be easily explained by wading that forces individuals to sustain this position and to walk bipedally. One of the most frequently mentioned functions in the list is stress reduction, a reference to the vertical stance of homo with weight bearing on both legs. But this compares nothing about ER with respect to other similar stance such as standing, wading, walking or even running short distance which all requires stress reduction. Other elucidations involve counter rotation, thermoregulation and head stabilization (Bramble & Lieberman 2004), but no comparative data were made to corroborate these explanations. With that, their explanations are ad hoc presumptions, which applied one primitive human without any consideration as to whether these supposed adaptations are seen in other animals, thus their explanations could be statistically void. Even Bramble & Lieberman (2004) admit that “humans are mediocre runners in several respects” and “running is more detrimental for us than for most other animals” (p345). Long legs and possibly shortened forearms could be seen as running traits, but these are also classic traits of aquatic species (Aiello & Dean 1990). Aiello & Dean (1990) cautioned that the reinterpretation of features in early homo’s fossils should be considered with extreme caution as the fossil record is still incomplete.

In a waterside model, wading and swimming would be preadaptative to the bipedal locomotion that Bramble & Lieberman (2004) consider to be a direct adaptation to ER. Most of the adaptations are not expected in cursorial animals (Alexander 2003). For instance, the list includes enlarged posterior and anterior semicircular canals, but this is not evaluated with, for example, giraffes, gibbons, kangaroos or aquatic species (Alexander 2003). It is a conceivable fact that the frequent change of posture seen when diving, be it - descending or ascending, required a different labyrinth structure, and that the H.erectus Labyrinth was adapted to terrestrial walking and running as well as aquatic locomotions (Aiello & Dean 1990). Another aspect said was there is an “expanded venous circulation of neurocranium” related with thermoregulation; (Bramble & Lieberman 2004, p348) however, there is no evidence but instead a long standing confirmation of expanded venous networks in diving species (Fahlman et al 2009). A feature that was said with respect to humans was having narrow body, thorax and pelvis which are indistinguishable as compared to most primates, as humans have a relatively very broad thorax and pelvis laterolaterally (Aiello & Dean 1990), and this was even more prominent in the australopithecines (Dart 1925). The combination of lateral flare effects of the iliac blades and relatively long horizontal femoral necks as seen in H.erectus indicates well-developed adduction and abduction (Aiello & Dean 1990), which is obviously not an adaptation for running, but would be advantageous for a species that frequently deal with aquatic activities. In H.Sapiens, the pelvis did become narrower and the femoral necks shorter and more vertical (Aiello & Dean 1990) and I agree with Bramble & Lieberman (2004) that this could be associated with a more frequent terrestrial locomotion. Furthermore, H.erectus has typically heavier bones and longer femoral necks than other primates including H.Sapiens, and as such it must have been an even less efficient cursorial (Aiello & Dean 1990). On the other hand, primitive Homo has a lower and longer brain skull than H.Sapiens (Aiello & Dean 1990). This means that the eyes would be orientated towards the sky if they were standing upright, rather than forward-facing for depth perception (Aiello & Dean 1990). This would be a drawback for a species relying on ER because it will consume more energy to look at where the feet were making contact with the ground. It also lacks crucial details on whether ER developed before or after large brains and which Homo species may have been endurance runners. The ER hypothesis too mentioned the function of the gluteus maximus increases substantially in supporting humans’ running capabilities (Lieberman et al 2006). Greiner (2002) argued experimentally that the gluteus maximus morphology is a consequence and not a prerequisite of our upright bipedal stance. This suggest that our bipedal posture would have preceded the appearance of the humanlike musculoskeletal morphology thus could make ER invalid. A study that compared the mechanical forces in the feet and the metabolic costs of generating these forces concluded that: “The increased mechanical cost associated with long toes in running suggests that modern human forefoot proportions might have been selected for in the context of the evolution of ER” (Rolian 2009, p713). Ironically, the study concluded that there is no difference in cost between long toes and short toes when walking (Rolian 2009) from which I could deduce that we evolved to be efficient walkers who could run when required and able to sprint during the occasional hunt. Foot anatomical features such as the plantar arches, enlarged tuber calcaneus, and short toes (Bramble & Lieberman 2004) are not seen in bi- or quadruped cursorials. Contradictory, unguli- or digitigrade species are better runners, not plantigrade (Alexander 2003).

Conclusively, anatomical traits described by Bramble & Lieberman (2004) present both strengths and weaknesses of the hypothesis and foreshadows its inherent outcomes on different levels that are geared towards the evolution of homo species. Until the features are considered in the milieu of aquatic activities as well as terrestrial locomotion, their elucidation should be considered with utmost apprehension. At present, there are no apparent grounds why any of the traits cited could not have been of benefit in a waterside environment. It is undeniable that humans today are adapted to terrestrial locomotion, but in my opinion the distinctive human anatomy is not directly derivable from a conventional homo species that moved from a closed to more open, arid environment as it is inconsistent with evolutionary processes cited.

References

1.Aiello, L & Dean, C 1990, Human evolutionary anatomy, Academic, London.
2.Alexander, R 2003, Principles of animal locomotion, Princeton University Press, Princeton, N.J.
3.Bramble, DM & Lieberman, DE 2004, ‘Endurance running and the evolution of homo’, Nature, vol. 432, no. 7015, pp.345-52.
4.Dart, RA 1925, ‘Australopithecus africanus, the man-ape of South Africa’, Nature, vol.115, no.2884, pp.195-99.
5.Fahlman, A, Hooker, SK, Olszowka, A, Bostrom, BL & Jones, DR 2009, ‘Estimating the effect of lung collapse and pulmonary shunt on gas exchange during breath-hold diving: The Scholander and Kooyman legacy’, Respiratory physiology & neurobiology, vol.165, no.1, pp.28-39.
6.Greiner, TM 200, ‘The morphology of the gluteus maximus during human evolution: Prerequisite or consequence of the upright bipedal posture?’, Human Evolution, vol.17, no.1-2, pp.79-94.
7.Lieberman, DE, Raichlen, DA, Pontzer, H, Bramble, DM & Cutright-Smith E 2006, ‘The human gluteus maximus and its role in running’, The Journal of experimental biology, vol.209, no.11,pp.2143-55.
8.Losos, JB 2011, ‘Convergence, adaptation and constraint’, International Journal of organic evolution, vol.65, no.7, pp.1827-40.
9.Pickering, TR, Bunn, HT 2007, ‘The endurance running hypothesis and hunting and scavenging in savanna-woodlands’, Journal of Human Evolution, vol.53, no.4, pp.434-438.
10.Pilbeam, DR, Lieberman, D, Smith, RJ, & Kelley, J 2005, Interpreting the past: essays on human, primate and mammal evolution in honor of David Pilbeam. Brill Academic Publishers, Boston.
11.Rolian, C, Lieberman, DE, Hamill, J, Scott, JW & Werbel, W 2009, ‘Walking, running and the evolution of short toes in humans’, Journal of experimental biology, vol.212, no.5,pp.713-721.