Could it be that the cannabinoid network is precisely the sort of adaptation that natural selection would favor in the evolution of a creature who survives by hunting? A brain chemical that sharpens the senses, narrows your mental focus, allows you to forget everything extraneous to the task at hand (including physical discomfort and the passage of time), and makes you hungry would seem to be the perfect pharmacological tool for man the hunter. All at once it provides the motive, the reward, and the optimal mind-set for hunting.