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Human Adaptations to Endurance Running and Present Day Dysevolution

By Aleksandar Borisov,

 

When my exercise physiology professor walked into our lecture one day wearing an absurdly large belt buckle with ‘100’ on it, my classmates and I couldn’t hold back a quiet chuckle. None of us suspected that this was a reward for finishing a 100-miles-in-a-day ultramarathon. That remains one of my most memorable lecture experiences, but it also intrigued me – how is it humanely possible to run such distances? Today, endurance running is first and foremost a form of exercise, but in the scope of human evolution it has contributed in countless ways to the present day human morphology. 16 million years ago, densely forested Eastern Africa began to dry, giving rise to hot grasslands, in which early humans were forced to adapt and traverse large distances to catch prey. 2 The Running Man Hypothesis, published in Nature (2004), explains several key adaptations which our most distant ancestors acquired to survive this relatively abrupt change in biome. 1

 

The Running Man Hypothesis

To weather our rapidly changing environment and survive as a species, we evolved countless anatomical adaptations better suited to a hotter climate devoid of jungles, and therefore cover for hunting. To maintain a cooler body temperature in these savannas we evolved into a bipedal species, reducing the amount of surface area exposed to the sun. Thermoregulation – our ability to adapt to changing temperatures, was further enhanced by 1) a reduction in body hair everywhere except the head, and 2) by our extraordinary ability to sweat significantly more than any other animal. 1 Other features which set us apart from our ancestors include our unique ability to uncouple breathing from running, allowing deeper breaths over several running cycles, resulting in a smaller oxygen debt. Furthermore, a human’s cost of transport (CoT – measured in mL of oxygen consumed per kg per km) curve is vastly different from that of other animals. 1 Whereas most animals have an optimal range of speed within which their CoT is lowest, the human curve is independent of speed between 8-18km/hr (typical running speeds). 1 This gave our ancestors a hunting advantage, allowing them to chase down prey to exhaustion, as it slowly lost the ability to stay within its optimal CoT range. Other vital changes in morphology included enlarged lower limb joints used to dissipate the stress of running, and our ability to store energy in tendons such as the Achilles and IT band, helping to decrease our CoT by 50%.1 These are just a few of the many anatomical adaptations which make 100-miles-in-a-day ultramarathons feasible, and which were paramount to our survival 16 million years ago.

 

Another, unrelated factor which contributes to our innate ability and desire to run is exercise-induced endocannabinoid signalling – in layman terms a “runner’s high”. Endocannabinoids that are released while running cause dopamine release in the reward regions of the brain, acting in a similar fashion to recreational drugs. 4 Moreover, they also act on the central and peripheral nervous systems, causing exercise-induced analgesia. 4 These examples showcase that we are, in fact, wired to run.

 

In the past 2000 years however, the Agricultural, followed by the Industrial Revolutions have significantly changed our lifestyles. In the scope of human evolution, these changes have occurred so abruptly that we have been unable to adapt from millions of years as hunter-gatherers to our ever increasingly sedentary lifestyles. The result is dysevolution – a propagation of non-infectious diseases our ancestors haven’t had to face, caused by rapid societal change. Our sedentary lifestyles lead to a loss of muscle mass and increased abdominal adiposity, causing immune cells to infiltrate the newly formed fat tissue, and thus resulting in a state of chronic inflammation. 3 The negative implications of this state are countless, ranging from insulin resistance (Type 2 diabetes), plaque build-up (atherosclerosis), and osteoporosis, conditions that have only recently begun to severely plague our society. 3 Evidently, exercise is crucial for battling dysevolution, and thanks to our many evolutionary adaptations, endurance running is just one of the many ways we are able to combat it.

 

References

  1. Dennis M. Bramble & Daniel E. Lieberman. (2004). Endurance running and the evolution of the Homo. Nature 432: 345-352.
  1. Hanna, J. M. & Brown, D. E. (1983). Human heat tolerance: an anthropological perspective. Annual Review of Anthropology. Vol. 12:259-284.
  1. Pederson, B. K. & Febbraio, M. A. (2012). Muscles, exercise and obesity: skeletal muscle as a secretory organ. Nat. Rev. Endocrinol. 10.1038.
  1. Raichlen, D. A., et al. (2012). Wired to run: exercise-induced endocannabinoid signalling in humans and cursorial mammals with implications for the ‘runner’s high’. Journal of Experimental Biology. 215: 1331-1336.
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