Science and technology.Exercise and addictionFun runPeople, it seems, have evolved to be addicted to exerciseAS THE legions of gym bunnies and jogging enthusiasts who race out into the spring sunshine every year clearly demonstrate, running can be fun.More specifically, running triggers the release of brain chemicals called endocannabinoids that create a potent feeling of pleasure.As their name suggests, these endocannabinoids work in the same way as the active ingredient of marijuana.From an evolutionary standpoint this surge of endocannabinoids, and the "runner's high" it creates, make sense.For ancient humans, remaining fit enough to run after game and away from predators and enemies was vital for survival.Yet whether other mammals are also driven to exercise by endocannabinoids has remained a mystery.Now a study led by David Raichlen of the University of Arizona has revealed that the runner's high does exist in other species, but not in all.You expect me to what?Dr Raichlen hypothesised that endocannabinoid-driven exercise highs would be found in those mammals that gain an evolutionary benefit from being fast on their feet: antelopes, horses and wolves, for example.However, he also thought that they would not be present in those which are known for being quick and agile, but not for running, like ferrets.To test these ideas, he and a team of colleagues devised an experiment that monitored the endocannabinoid levels of different species after they had been walking or running on a treadmill.
