Karma.
You have good luck in this life, you have bad luck in the next. A long life this time, a short one next time.
Do bad, and you come back as a lesser life form. Do good, and you advance. Not sure how a dog or cat could be 'good' to progress up the hierarchy order but it's got me thinking.
Of course, there doesn't appear to be any evidence for what I am posting, except that we have the ability to contemplate such things.
