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One of the unique physical attributes of humans is the ability to travel for long distances. Special populations outline this ability, such as the high landers of Kenya and Ethiopia, who can out run about 90% of the rest of the humanity. This observation has lead many a discussion over the role nature versus nurture of this phenomenon.

Long-distance runners train in the high-altitude village of Iten, Kenya

Evelyn Hockstein for ESPN.com. Long-distance runners train in the high-altitude village of Iten, Kenya.

So just what is it that rewards us to exercise — Why do we get that “runner’s high” after a long work out? A recently published paper in the Journal of Experimental Biology, lead by anthropologist David A. Raichlen, investigated the blood of humans, dogs and ferrets before and after 30 minutes of exercise. It was observed that an endocannabinoid, or endorphin, named anandamide spiked in humans and dogs, but not in ferrets.

Among the many roles of the anandamide neurotransmitter, the role of it in neural generation of motivation and pleasure in particularly important. In previous studies, anandamide injected directly into the forebrain reward-related brain structure nucleus accumbens enhanced the pleasurable responses of rats. Raichlen writes,

“These results suggest that natural selection may have been motivating higher rather than low-intensity activities in groups of mammals that evolved to engage in these types of aerobic activities.”

A co-author, Greg Gerdeman, adds,

“The experimental results prove that “anandamide-inspired motivation to run was the evolution of an ‘endurance athlete phenotype’ that played a major role in the survival and reproductive success of our Homo sapiens ancestors…”

Raichlen, D., Foster, A., Gerdeman, G., Seillier, A., & Giuffrida, A. (2012). Wired to run: exercise-induced endocannabinoid signaling in humans and cursorial mammals with implications for the ‘runner’s high’ Journal of Experimental Biology, 215 (8), 1331-1336 DOI: 10.1242/jeb.063677