In keeping with the original concept of this being a non-religious thread, and hence shying away from Karma as defined within Taoism or Zen Buddhism, I think some reasonable facsimile of "karma" exists insofar as the nature of your actions and decisions profoundly impact the level of meaning you can derive from life. For me, karma is a function of Eudaimonia (Aristotelian concept...the rough gist is that there is a fundamental difference between the pleasure derived from meaningless gratification in the form of physical sensation, monetary reward, etc and happiness that is to be gained from striving towards a moral existence). As far as I'm concerned, genuine happiness is inextricably wound up with pervasive morality. If you think about it, human beings make most of their decisions within a fairly hierarchical rubric. If you think about the nature of human logic, for example, all human logic is either tautological or reductive, and so too, I believe, are human desires. So as an example, few people desire money for the sake of money, they desire money for the sake of its power, which in turn they desire for the sake of comfort, or prestige, which in turn they desire for the sake of the emotion that creates within them, and so on. Ultimately, I believe there is a single, driving motivation behind most human beings' decisional hierarchies that ultimately foreshadows their choices, actions and preferences. For myself, I believe that the net end of human existence is to seek Eudaimonia; that a state of fulfilled happiness is effectively nirvana; and that while there is (again, my belief, not a blanket statement) such a thing as objective morality, human consciousness is so profoundly limited that no one will ever achieve perfect morality, and even if one could, no one could ever possess the capacity to understand that one had. As a result, I believe that the definition of meaningful, moral living then is to strive towards that state knowing full well that it cannot be achieved, and hence at some point every decision I make is deferent to my desire for Eudaimonia. So while karma as defined as some kind of tangible, worldly justice to be meted out by a Great Chain of Being on the basis of whether or not you have disturbed it is not a compelling concept for me, I do believe there is karma insofar as you will reap from your life only so much as you decide to invest in it. I cannot know what of my actions have been objectively moral and what have not (though I do have a working hypothesis), but the one thing I know for certain will doom my life to emptiness and sadness is apathy.