Reincarnation is the law of return, of evolution in action, and karma is the cause of that return. Karma is the law of adjustment, it neither rewards nor punishes, but adjusts the scales to bring balance. Karma and reincarnation fit scientific principles concerning energy. Energy can neither be created nor destroyed, only transformed. For every action there is an equal reaction.
All matter is subject to decay.
Order arises out of chaos. From the Micro to the Marco, as it is above, so it is below. Karma is also our teacher of self-responsiblity. Karma doesn't make us do something wrong. If we do something wrong, say break the law, and get punished, we are responsible for the act by using our Free Will to choose to disregard the law.