Human Evolution: The Biology of Man

Endurance Running

While it is apparent from the above observations that walking must have been essential for human survival, it would be ignorant to ignore all the adaptations that allow humans to be great endurance runners as well. There are a host of adaptations that set humans apart from all other mammals in this regard:

Adaptations to Running: Radiation, Surface Area, Stabilization and Springs

First and foremost, we must address the size and shape of the human body (relative to other animals). We walk vertically on two feet and have long legs, increasing our surface area significantly. As a result, we are more capable of radiating away unwanted heat. However, more importantly, vertical walking allows us to have less of our bodies exposed to the sun (head and neck instead of a 4 legged animal’s entire back), drastically reducing heat stress. Obviously, this advantage is compounded by our lack of insulating fur as well as millions of excess sweat glands all across the body.

The remaining adaptations allow the mechanism of running to become much less costly. The act of running is accurately summarized as jumping from one leg to another. Thus, the arches of the feet and tendons in your calf muscles play important roles in storing elastic energy during running. This process is so efficient at storing and releasing energy that there is almost no difference in energy expenditure when comparing people running constantly at two different speeds (think of a very efficient Newton’s cradle).

When running, your glutes engage much more than when walking due to the constant need for stabilization. In addition, humans have very large balance organs inside their ears in order to make spatial orientation effortless during high speed motion.

Walking and Running: Niche Adaptations

Such adaptations for running and walking enable humans to fill a very specific niche in the ecosystem: hunting and gathering. The ability to walk and run for many miles a day is very useful if your diet is dependent on high energy sources of food (as mentioned earlier). In order to make this lifestyle even more viable, a few more bodily changes took place:

The most important skill needed for a hunter gatherer on the search for food is to see what is in front of him. If the person is able to run for a long time, but have very shaky vision, hunting wild animals would be nearly impossible. As a result, human evolution provided us with low shoulders that allow the torso to move independently of the head to stabilize the body. This allows our heads to steadily look forward even as we run. To further stabilize the head, neck tendons connect to our arms in order to compensate for the inevitable wobbling during motion.