Runner’s High May be an Evolutionary Adaptation
The benefits of physical activity and exercise on the human brain have been widely reported. In particular, it’s increasingly clear that aerobic activity has positive benefits on mood and cognition, even throughout one’s lifetime.
But new research1 suggests that these effects on our brains may be evolutionary adaptations, driven at least in part by humans shifting to a hunter-gatherer lifestyle that rewarded aerobic capacity over two million years ago.
Specifically, researchers looked at one set of neurotransmitters, Endocannabinoids
(eCBs), that seem to be involved in producing these neurobiological effects. They proposed that eCB signaling brought about by exercise is a product of our evolutionary history.
To test this hypothesis, researchers started by examining exercise-induced eCB signaling among different species. Specifically, for example, humans and dogs are species that evolved the capacity to run long distances. In these animals, moderate-intensity aerobic activity does indeed cause a significant increase in eCB circulation. But looking at taxa without an evolutionary history or high aerobic capacity, aerobic activity seems to have no effect on eCBs. Ferrets, for example, are not adapted to long-distance running and thus show no change in eCBs as a result of aerobic activity.
For researchers, this indicated the possibility that increased eCB signaling from aerobic activity may be an adaptation for endurance athletic performance. Researchers then went on to examine two hypotheses to explain the evolutionary connection to aerobic capacity and brain function.
The positive cognitive effects of running may be a byproduct of evolution.
The first hypothesis is that the mood-enhancing effect of increased eCB circulation (“runners high”) was a kind of reward or motivation that encouraged individuals to engage in long periods of aerobic activity. In other words, rewarding or making pleasurable this physically taxing activity may have encouraged extended hunting or foraging.
The second hypothesis is that cognitive improvements from aerobic activity made fro more effective and efficient hunters and gatherers. Successful foraging may have been, for example, the result of better spatial memory, a known result of increased eCB activity.
The researchers conclude that although more work is necessary, the addition of an evolutionary understanding of the effects of aerobic activity and exercise on the human brain may bring us ways of delivering better interventions and treatments. In addition, they suggest that differences in species-level evolution in this regard should be considered with using animal models to study exercise physiology.
1. Raichlen, David A., Adam D. Foster, Alexandre Seillier, Andrea Giuffrida, and Gregory L. Gerdeman. "Exercise-induced endocannabinoid signaling is modulated by intensity." European journal of applied physiology 113, no. 4 (2013): 869-875.