I know from my experience training/handling dogs that the most content and reliable animals are the ones that are given an outlet for their instincts: they need to run, sniff around, and, generally, keep their apex predator functions in good working condition. Humans are much closer to dogs and their wolf relatives than some are perhaps willing to admit. At a personal level, I find that pushing myself to new challenges—be it a hard day of physical labour or the elucidation of some concept (or usually both)—makes me more peaceful and, indeed, contemplative.