Ages ago, when man and dog first teamed up, the dog took the good with the bad.  After all, the cuisine was good, there was useful work to do and there was lots of opportunity for a dog to stretch his legs and run.  Sure, there was stress back then, too.  A dog was likely as not to get kicked away from the best spot near the fire.  An occasional kid might have pulled an occasional tail.  And there was always the treat that instead of eating woolly mammoth for lunch, the woolly mammoth would eat him. For modern dogs, the sources of stress might not be as clear.  True, it may still come from having to give up the most comfortable spot in the “cave.”  Some rude child might still yank a tail.  And while there are no longer woolly mammoths, there is still danger – from traffic, disease, and saddest of all, the lack of commitment of some human partners.  In the old days, a dog could just go outside and run around until he felt like himself again.  Even that is more difficult now.  Now he’s often dependent upon us for stress reduction.  He can no longer do it on his own.