Endurance running hypothesis

The endurance running hypothesis is a series of conjectures which presume humans evolved anatomical and physiological adaptations to run long distances^[1][2][3] and, more strongly, that "running is the only known behavior that would account for the different body plans in Homo as opposed to apes or australopithecines".^[4]

The hypothesis posits a significant role of endurance running in facilitating early hominins' ability to obtain meat. Proponents of this hypothesis propose that endurance running served as a means for hominins to effectively engage in persistence hunting and carcass poaching, thus enhancing their competitive edge in acquiring prey. Consequently, these evolutionary pressures have led to the prominence of endurance running as a primary factor shaping many biomechanical characteristics of modern humans.

Evolutionary evidence

No primates other than humans are capable of endurance running, and in fact, Australopithecus did not have structural adaptations for running.^[5][6] Instead, forensic anthropology suggests that anatomical features that directly contributed to endurance running capabilities were heavily selected for within the genus Homo dating back to 1.9Ma. Consequently, selecting anatomical features that made endurance running possible radically transformed the hominid body.^[7] The general form of human locomotion is markedly distinct from all other animals observed in nature. ‘’From the Journal of Anatomy’’, author RM Alexander describes our unique form of bipedal motion:

"… no animal walks or runs as we do. We keep the trunk erect; in walking, our knees are almost straight at mid-stance; the forces our feet exert on the ground are very markedly two-peaked when we walk fast; and in walking and usually in running, we strike the ground initially with the heel alone. No animal walks or runs like that."^[8]

From the perspective of natural selection, scientists acknowledge that specialization in endurance running would not have helped early humans avoid faster predators over short distances.^[9] Instead, it could have allowed them to traverse shifting habitat zones more effectively in the African savannas during the Pliocene. Endurance running facilitated the timely scavenging of large animal carcasses and enabled the tracking and chasing prey over long distances. This tactic of exhausting prey was especially advantageous for capturing large quadrupedal mammals struggling to thermoregulate in hot weather and over extended distances. Conversely, humans possess efficient means to dissipate heat, primarily through sweating. Specifically, evaporative heat dissipation from the scalp and face prevents hyperthermia and heat-induced encephalitis by extreme cardiovascular loads.^[10] Furthermore, as humans continued to develop, our posture became more upright and subsequently increased vertically with the elongation of limbs and torso, effectively increasing surface area for corporeal heat dissipation.^[11]

In work exploring the evolution of the human head, paleontologist Daniel Lieberman suggests that certain adaptations to the Homo skull and neck are correlational evidence of traits selective to endurance running optimization. Specifically, he posits that adaptations such as a flattening face and the development of the nuchal ligament promote improved head balance for cranial stabilization during extended periods of running.^[12]

Compared to Australopithecus fossil skeletons, selection for walking by itself would not develop some of these proposed "endurance running" derived traits —

• evaporative heat dissipation from the scalp and face prevents hyperthermia
• flatter face makes the head more balanced
• Nuchal ligament helps counterbalance the head
• shoulders and body can rotate without rotating the head
• taller body has more skin surface for evaporative heat dissipation
• torso can counter-rotate to balance the rotation of the hindlimbs
• shorter forearms make it easier to counterbalance hindlimbs
• shorter forearms cost less to keep flexed
• backbones are wider, which will absorb more impact
• stronger backbone pelvis connection will absorb more impact
• compared to modern apes, human buttocks "are huge" and "critical for stabilization."
• longer hindlimbs
• Achilles tendon springs conserve energy
• lighter tendons efficiently replace lower limb muscles
• broader hindlimb joints will absorb more impact
• foot bones create a stiff arch for efficient push off
• broader heel bone will absorb more impact
• shorter toes and an aligned big toe provide better push off

Academic discourse

The derived longer hindlimb was already present in Australopithecus along with evidence for foot bones with a stiff arch. Walking and running in Australopithecus may have been the same as early Homo. Small changes in joint morphology may indicate neutral evolutionary processes rather than selection.^[13]

The methodology by which the proposed derived traits were chosen and evaluated does not seem to have been stated, and there were immediate highly technical arguments "dismissing their validity and terming them either trivial or incorrect."^[14]

Most of those proposed traits have not been tested for their effect on walking and running efficiency. ^[13] The new trunk shape counter-rotations, which help control rotations induced by hip-joint motion, seem active during walking.^[15][16] Elastic energy storage does occur in the plantar soft tissue of the foot during walking.^[15] Relative lower-limb length has a slightly larger effect on the economy of walking than running.^[16] The heel-down foot posture makes walking economical but does not benefit running.^[17]

Model-based analysis showing that scavengers would reach a carcass within 30 minutes of detection suggests that "endurance running" would not have given earlier access to carcasses and so not result in selection for "endurance running". Earlier access to carcasses may have been selected for running short distances of 5 km or less, with adaptations that generally improved running performance.^[18]

The discovery of more fossil evidence resulted in additional detailed descriptions of hindlimb bones with measurable data reported in the literature. From a study of those reports, hindlimb proposed traits were already present in Australopithecus or early Homo. Those hindlimb characteristics most likely evolved to improve walking efficiency with improved running as a by-product.^[19]

Gluteus maximus activity was substantially higher in maximal effort jumping and punching than sprinting, and substantially higher in sprinting than in running at speeds that can be sustained. The activity levels are not consistent with the suggestion that the muscle size is a result of selection for sustained endurance running.^[20] Additionally, gluteus maximus activity was much greater in sprinting than in running, similar in climbing and running, and greater in running than walking. Increased muscle activity seems related to the speed and intensity of the movement rather than the gait itself. The data suggests that the large size of the gluteus maximus reflects multiple roles during rapid and powerful movements rather than a specific adaptation to submaximal endurance running.^[21]

References

1. Carrier, David R. (August–October 1984). "The Energetic Paradox of Human Running and Hominid Evolution". Current Anthropology. 25 (4): 483–95. doi:10.1086/203165. JSTOR 2742907. S2CID 15432016..
2. Bramble, Dennis; Lieberman, Daniel (November 2004). "Endurance running and the evolution of Homo" (PDF). Nature. 432 (7015): 345–52. Bibcode:2004Natur.432..345B. doi:10.1038/nature03052. PMID 15549097. S2CID 2470602.
3. Krantz, Grover S. (1968). "Brain size and hunting ability in earliest man". Current Anthropology. 9 (5): 450–451. doi:10.1086/200927. S2CID 143267326.
4. Zimmer, Carl (17 November 2004). "The Evolution of Endurance: Physiologic adaptations may have made humans better runners". Science.
5. Hunt, Kevin (1 December 1991). "Mechanical implications of chimpanzee positional behavior". American Journal of Biological Anthropology. 86 (4): 521–536. doi:10.1002/ajpa.1330860408. PMID 1776659.
6. Stern, Jack; Susman, Randall (1983). "The locomotor anatomy of Australopithecus afarensis". American Journal of Biological Anthropology. 60 (3): 279–317. doi:10.1002/ajpa.1330600302. PMID 6405621.
7. Lieberman, Daniel (2007). "Lieberman, Daniel E., et al. "The evolution of endurance running and the tyranny of ethnography: A reply to". Journal of Human Evolution. 53 (4): 439–442. doi:10.1016/j.jhevol.2007.07.002. PMID 17767947. S2CID 14996543.
8. Alexander, R M. (2004). "Bipedal animals, and their differences from humans". Journal of Anatomy. 204 (5): 321–330. doi:10.1111/j.0021-8782.2004.00289.x. PMC 1571302. PMID 15198697. S2CID 46335255.
9. Lieberman, Daniel. "Britannica Biography: Daniel Lieberman". {{cite journal}}: Cite journal requires |journal= (help)
10. Rasch, W.; Samson, P. (August 1991). "Heat loss from the human head during exercise". Journal of Applied Physiology. 71 (2): 590–595. doi:10.1152/jappl.1991.71.2.590. PMID 1938732.
11. Wheeler, P.E. (1993). "Wheeler, P. E. "The influence of stature and body form on hominid energy and water budgets; a comparison of Australopithecus and early Homo physiques". Journal of Human Evolution. 24 (1): 13–28. doi:10.1006/jhev.1993.1003.
12. Leiberman, Daniel (1 April 2011). The Evolution of the Human Head. Harvard University Press. doi:10.4159/9780674059443. ISBN 9780674059443.
13. Pontzer, Herman (2012). "Ecological Energetics in Early Homo". Current Anthropology. 53 (S6): S346–S358. doi:10.1086/667402. S2CID 31461168.
14. "Unlike apes, humans were born to run, study says / Finding could help date human evolution -- but other scientists say the theory is bunk". SFGATE. 18 November 2004.
15. Crompton, R. H.; Vereecke, E. E.; Thorpe, S. K. S. (2008). "Locomotion and posture from the common hominoid ancestor to fully modern hominins, with special reference to the last common panin/hominin ancestor". Journal of Anatomy. 212 (4): 501–543. doi:10.1111/j.1469-7580.2008.00870.x. PMC 2409101. PMID 18380868.
16. Steudel-Numbers, Karen L.; Weaver, Timothy D.; Wall-Scheffler, Cara M. (2010). "The evolution of human running: Effects of changes in lower-limb length on locomotor economy". Journal of Human Evolution. 143 (4): 601–611. doi:10.1002/ajpa.21356. PMC 3011859. PMID 20623603.
17. Cunningham, C.B.; Schilling, N.; Anders, C.; Carrier, D.R. (1 March 2010). "The influence of foot posture on the cost of transport in humans". The Journal of Experimental Biology. 213 (5): 790–797. doi:10.1242/jeb.038984. PMID 20154195. S2CID 14834170.
18. Ruxton, Graeme D.; Wilkinson, David M. (2012). "Endurance running and its relevance to scavenging by early hominins". Evolution. 67 (3): 861–867. doi:10.1111/j.1558-5646.2012.01815.x. PMID 23461334. S2CID 41162625.
19. Deckers, K.P. (15 July 2017). "These bones were made for jogging: an analysis of the lower limb skeletal evidence for the endurance running hypothesis". Inter-Section. 3: 7–13. hdl:1887/3210949.
20. Carrier, David R.; Schilling, Nadja; Anders, Christoph (2015). "Muscle activation during maximal effort tasks: evidence of the selective forces that shaped the musculoskeletal system of humans". Biology Open. 4 (12): 1635–1642. doi:10.1242/bio.014381. PMC 4736035. PMID 26538637.
21. Bartlett, Jamie L.; Sumner, Bonnie; Ellis, Richard G.; Kram, Rodger (2014). "Activity and Functions of the Human Gluteal Muscles in Walking, Running, Sprinting, and Climbing". American Journal of Physical Anthropology. 153 (1): 124–131. doi:10.1002/ajpa.22419. PMID 24218079. S2CID 29957031.