Modern man runs to exercise; early man ran to escape predators or to get food. Over the course of human evolution, how did running evolve from being a necessary part of survival to being a physical activity that most people actually enjoy? The question anthropologists tried to answer was why our early ancestors ran for survival and how come they did not evolve other means of survival when running was metabolically costly and increased the risk of injury which, during prehistoric times, could have meant death?
A study conducted by scientists from the University of Arizona searched for the answer using ferrets, which are not anatomically adapted to running; in biological terms, they are non-cursorial species. With the help of these animals, the researchers tried to learn if humans and other species’ penchant for running was encouraged by evolution. “We wondered if natural selection might have used neurobiological mechanisms to encourage exercise activity,” said lead researcher David A. Reichlen, an anthropology professor at the University of Arizona. More specifically, is there something in our biochemistry that also evolved and which hard-wired us to like running?
Dr. Raichlen and his colleagues looked at whether endocannabinoids played a role in the evolutionary development of humans. Endocannabinoids are chemicals that act in the same way as cannabis in marijuana, altering and lightening moods. These chemicals are naturally produced by the body and previous studies have suggested that the increase in endocannabinoid levels after prolonged cycling and running cause what is called a runner’s high. Dr. Raichlen wanted to find out if our species continued to run even when we didn’t need to because it gave us a high.
Using ferrets, a species which do not engage in a lot of running, Dr. Raichlen and his colleagues tested the theory. They wanted to see if the ferrets would also produce the same response to increased endocannabinoid levels after running; in other words, they wanted to see if the ferrets would experience a runner’s high. For comparison, the scientists chose dogs and recreational (human) runners, both of which are cursorial species or species that are well-adapted for running.
The study involved having each subject from both groups run and walk on a treadmill on separate days for 30 minutes each session; when it came to the walking exercise, however, the ferrets were made to rest in their cages because they couldn’t master the activity on the treadmill. The researchers drew blood samples from each participant before and after the activities. They then checked the blood samples for endocannabinoids.
Unsurprisingly, the human participants showed an increase in endocannabinoid levels after running; for the first time, results also showed that dogs also experience a runner’s high as demonstrated by a similar increase in their endocannabinoid levels. No increase was observed after the walking exercises.
The ferrets, however, showed no increase in endocannabinoid levels after running, suggesting that the activity does not give them neurobiological pleasure.
According to Dr. Raichlen, the findings suggest that the neurobiological pleasure we experience from running is part of our evolutionary development and serves as an “award response.” The million dollar question, though, added Dr. Raichlen, is why not everybody runs for the sheer pleasure of it. He says while “we have the evolutionary drive” to run, we have learned to ignore the urge.
Dr. Raichlen admits that the findings of their study are only preliminary and the study itself had its limitations, such as the fact that the human participants were fitter than the average human and, therefore, were not really representative of the general population. Dr. Raichlen added that the findings proved that “our evolutionary history appears to have included this kind of endurance activity and rewarded it,” giving us the “biological imperative” to run.