The so-called runner\u2019s high has an evolutionary explanation, according to researchers who have been exploring the phenomenon. A study by a team at the University of Arizona, led by David Raichlen, PhD, a professor in the School of Anthropology there, has found evidence to suggest that the runner\u2019s high is an evolutionarily adaptive mechanism unique only to humans and to other mammals for whom running was necessary to survival. Why Running Can Be as Pleasurable as Smoking Pot Running and other forms of vigorous exercise produce a surge of neurochemicals in the brain known as endocannabinoids. These create the same feelings of pleasure as the active ingredient in marijuana. But why this is so has posed a question. Dr. Raichlen\u2019s team, which studies how changes in human locomotion (movement) and aerobic activity affect human anatomy and neurobiology, made the following hypothesis: they guessed that only those mammals that had an evolutionary reason to run in order to flee predators or catch prey \u2014 mammals like antelopes, horses and wolves, for example \u2014 would experience a runner\u2019s high. Then they tested that hypothesis, by putting three different mammals on a treadmill and monitoring their endocannabinoid levels. Ten humans, eight dogs and eight ferrets were the test subjects. They were made to run 30 minutes on a treadmill, after which time their endocannabinoid levels were measured. The dogs and humans\u2019 levels were significantly higher, while the ferrets\u2019 levels rose only marginally, leading researchers to conclude that dogs experience a runner\u2019s high, too, and that this high is the result of natural selection. Ferrets, in contrast, Raichlen reasoned, do not need the evolutionary advantage of running long distances in order to hunt for food. If they, too, must be fast on their feet, they rely more on skills like burrowing, and stealthily surprising potential sources of food such as rabbits or other small prey. The findings of Raichlen\u2019s study, published in the Journal of Experimental Biology, were also described in an article in The Economist. From Walking to Running \u2014 to Getting High? Evolutionary biologists like Raichlen contend that the evolution of the human race is marked by at least two critical transitions in how human beings use their bodies to travel. The first of these milestones came with the origin of the human species. That is when the first homo sapiens began to use their two legs to walk in a bipedal pattern. The second transition came not long after, some 1.8 million years ago, when the first human beings adopted a lifestyle of hunting and gathering. One hypothesis known as the \u201cendurance running hypothesis\u201d suggests that running long distances evolved as an adaptation to the need for scavenging and \u201cpersistence hunting\u201d for food. \u201cPersistence hunting,\u201d while very rare today \u2014 only groups like the bushmen of the Kalahari in southern Africa or Native American populations in Northern Mexico, such as the Tarahumara or Raramuri, still practice the technique \u2014 was once commonly practiced, and was the main source of livelihood for the earliest human ancestors. \u201cPersistence hunting\u201d involved just what its name suggests \u2014 namely, relentlessly tracking prey to the point of exhaustion. In the heat of day, the hunted animals could not sustain their long-distance flight. Over the course of a few hours, they would eventually need to stop, rest or collapse in the shade, so that their human predators would then be able to close in with spears for the kill. Unsolved Mysteries of Exercise Addiction The endurance running hypothesis may help to explain the development of the runner\u2019s high \u2014 and, why, for that matter, so many of the world\u2019s top long distance runners come from areas where persistence hunting is still in practice, if not in vogue. But one mystery yet to be put to rest is to what degree the more general phenomenon of exercise addiction is a function of being more highly evolved \u2014 and whether those of us inclined towards couch potato-ism can claim any evolutionary justification for our sedentary ways. Maybe someday researchers will unlock that puzzle, too.