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Born to Run: Running and Human Evolution William Rose

Born to Run: Running and Human Evolution William Rose. Sources: Bramble & Lieberman (2004) Nature 432 : 345-352; Wilford, New York Times , Nov. 18, 2004. Human Evolutionary Timeline. 10 Mya. 5 Mya. 3.5 Mya. 1.8 Mya. Present. Austr. afarensis. Homo erectus. Homo sapiens.

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Born to Run: Running and Human Evolution William Rose

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  1. Born to Run: Running and Human Evolution William Rose Sources: Bramble & Lieberman (2004) Nature432: 345-352; Wilford, New York Times, Nov. 18, 2004.

  2. Human Evolutionary Timeline 10 Mya 5 Mya 3.5 Mya 1.8 Mya Present Austr. afarensis Homo erectus Homo sapiens Chimp-anzees Gorillas

  3. Background Australopithecines walked habitually > 4 Mya H. erectus a better walking design than Australopith.: walking / swinging tradeoff Was human running selected for? Did running influence human evolution? Most have said probably not. Humans not very good sprinters. Horses, antelopes, greyhounds can run faster longer. Sources: Bramble & Lieberman (2004) Nature432: 345-352; Wilford, New York Times, Nov. 18, 2004.

  4. Run vs. walk • Walk • Inverted pendulum, KE – PE tradeoff • C.o.m. vaults over extended leg in stance • U-shaped cost-of-transport (COT) curve • Optimum speed a function of leg length • Run • Mass-spring mechanism, KE – PE tradeoff • Tendons, muscles, ligaments store PE • Limbs flex more in run to store energy • Walk-to-run transition occurs where COT curves intersect – as one might expect Sources: Bramble & Lieberman (2004) Nature432: 345-352; Wilford, New York Times, Nov. 18, 2004.

  5. Running gait • Human running like trotting • Bipeds can’t gallop • Forelimbs move with opp. hindlimbs • Human running, trotting both bouncy • Run • Mass-spring mechanism, KE – PE tradeoff • Tendons, ligaments store PE • Limbs flex more in run to store energy • Walk-to-run where COT curves intersect Sources: Bramble & Lieberman (2004) Nature432: 345-352; Wilford, New York Times, Nov. 18, 2004.

  6. Endurance Running (ER) ER: many kilometers, aerobically, 3-6.5 m/s Humans: only primates that do ER Better than most mammals Humans can run faster than most trotting animals trot, esp. when consider body size Distance: >10% Americans run kms/day Distance: Thousands/yr run 42 km Unknown in other primates; unusual in other mammals Sources: Bramble & Lieberman (2004) Nature432: 345-352; Wilford, New York Times, Nov. 18, 2004.

  7. Running Adaptations • What adaptations make ER possible? • When do they appear in fossil record? • Four areas of adaptation required for ER • Energetics • Strength • Stabilization • Thermoregulation

  8. Energetics Long tendons, short muscles Chimps: short calcaneal tendon Australopithicus: Calcaneal tendon insertion site is chimplike Plantar arch: another energy storage site in humans Chimps: flat feet, weight bearing, large medial tuberosity on navicular. Austr. like chimps, but early Homo lack large medial tuberosity on navicular

  9. Bramble & Lieberman (2004) Nature432: 345-352.

  10. Energetics: Stride length Humans have longer stride than expected for animal their size Humans increase speed mostly by increasing stride length Long (relative to body size) legs in humans, H. erectus. Chimps short. Austral ?? Oscillating long legs is costly unless minimize moment of inertia, hence small human feet Human feet small compared to chimps & pithecines (9% v 14% leg mass, hmn v chmp)

  11. Bramble & Lieberman (2004) Nature432: 345-352.

  12. Skeletal strength • Running: large skeletal stresses • Force at heel strike = 3-4X body wt • Force travels up skeleton • Adaptations • Larger lower limb joint surfaces in human v chimp, even after adjust for weight: knee, hip, sacroiliac, lumbar centra • Reduced femoral neck length & inter-acetabular distance reduces bending moments on femoral neck, sacrum, lower back – compare Homo to chimps, Australopithicus

  13. Bramble & Lieberman (2004) Nature432: 345-352.

  14. Stabilization Gluteus max: its “increased size is among the most distinctive of all human features” Enlarged sacral transverse process Enlarged area for erector spinae attachment on sacrum, PSIS – allows the forward pitch of trunk during running Decoupled head & shoulder (longer neck, fewer/smaller muscles) Homo vs Pan, Austr

  15. Stabilization Reduced forearm mass in Homo (50% smaller than Pan when adjust for body weight) reduces effort to keep arm flexed Decoupled head & shoulder (longer neck, fewer/smaller muscles) Homo vs chimp, Austr Wide shoulders of Homo enhance counter-balancing effect of arm-swinging in running

  16. Head Stabilization Occipital projection behind condyles improves balance, reduces pitch-forward tendency at footstrike Larger relative diam of posterior semicircular canal increaes sensitivity to sagital plane accelerations of head Large nucchal ligament seen in humans, cursors, & large-headed mammals (elephant) but not chimps; Australopith lack nucchal line on occipital bone

  17. Thermoregulation Dissipate waste heat of running Humans: Larger & more eccrine sweat glands for evaporative cooling Lack of body hair Larger near-surface cranial venous circulation Mouth breathing (also lowers work of breathing)

  18. Summary of some human adaptations for running

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