Sorry LeBron, Humans Are Born To Run Marathons.

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Watching a preternaturally talented athlete like LeBron James compete, it may be easy to think that human evolution was designed to create athletes with amazing skill, agility, and power.  But this is not so.  We humans exist today because our prehistoric ancestors evolved into creatures with unmatched ability to run great distances in hot weather.  That’s right.  We humans are supposed to be endurance athletes!

Our prehistoric ancestors had to eat to survive.  But they were not remotely as strong and fast as predators of that time, like lions, leopards, and saber tooth tigers.  Our prehistoric ancestors also lacked the sorts of weapons that would even the playing field with other carnivores.  They had no bows and arrows, no atlatl, and their spears were only made of wood (no bone or stone points). The advantage they had, however, was endurance running.  We humans are unique among almost all other mammals in our ability to run great distances, even in very hot weather. Our prehistoric ancestors developed this ability and would track and chase prey to the point of exhaustion of the prey. The exhausted prey would then be vulnerable to attacks from the poor-quality weapons the hunters possessed.

How were our ancient ancestors able to do this?  Aren’t antelopes much faster than humans?

While much of the prey our ancestors hunted were much faster for short periods of time, pre-humans, in the end, had an advantage.  The most important advantage was their ability to resist overheating with extended exercise, even in very hot weather.

This resistance to fatigue arises from a number of adaptations.  One of these adaptations is in muscle fibers.  Most mammals have more fast twitch than slow twitch muscles, whereas in humans the ratio is closer to 50:50.  With endurance training, however, humans can tip the balance to about 80% slow twitch.  This is one reason why most other mammals are so quick and explosively strong compared to humans (even LeBron James).

But strength comes with consequences.  Most mammals can only run at top speed (gallop) for 10-15 minutes before having to slow down or rest.  The most comfortable slower speed for most mammals is a trot and this speed is SLOWER than the speeds humans can maintain for extended periods of time.

Aside from having more slow-twitch musculature (and, therefore, better aerobic metabolism) there are a number of other adaptations that allow humans to be great endurance runners. One of the most important of these adaptations is the ability to sweat. Very few other animals can sweat (interestingly, kangaroos sweat).  Instead, they rely on panting to cool themselves. Panting occurs in the upper airway where gas exchange does not occur.  Panting also involves breathing approximately 10 times faster than normal.  Finally, in most animals the respiratory cycle is coupled 1:1 with movement of the limbs.  Therefore, when most mammals become overheated, they simply cannot gallop because they cannot both get the oxygen that they need (and remove carbon dioxide) and cool themselves at the same time.

Another interesting aspect of endurance that our ancient ancestors learned to exploit was the “sweet spot” of their prey’s gait.  For most mammals, there is a “U”- shaped curve of energy expenditure at both the gallop and trot speeds.  If these animals go much faster or slower than these two set speeds, they tire much faster.  In contrast, while walking, for humans, also has a “U”-shaped curve of energy expenditure, running does not. So, our ancient ancestors would chase their prey at speeds that would force them out of a comfortable trot.  This would create exhausted, vulnerable, prey much more efficiently.

This pattern of hunting went on for many thousands of years and it led to the evolution of pre-humans who were increasingly suited to endurance running.  As weapons, especially ranged weapons, became more effective and our ancient ancestors expanded out of regions that favored endurance hunting, this ability became less important.  Nonetheless, ability in endurance athletics is forever a part of all of our DNA.

We were born to run…marathons!

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Reference:

Lieberman DE, Bramble DM, Raichlen DA, et al. Brains, brawn, and the evolution of human endurance running capabilities. In: Grine , Fleagle , Richard , Leakey , editors. The First Humans—Origin and Early Evolution of the Genus Homo. Springer; 2006.

Photo Credit: N08/7691525134/”>Nathan Wind as Cochese via Compfight cc

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