actually you can look at reincarnation in a scientific sense as well as spiritual sense...
science plainly states that you never cease to exist, even when you die. You were never created, you were simply put together by other human's cells and grew off of eating other living things. And when you die you will become something else, or many things. This is fact. When we reproduce we aren't actually creating a new life form, we are simply passing on a part of ourselves and watching it grow.
Science plainly states this... you are made of other living things, and in your lifetime and when you die you pass yourself on to other living things(reproducing, decomposing), and grow from other living things(eating) but you will never cease to exist.
Now in a spiritual sense I don't know, but it's interesting how the basic(basic, not religous) idea of reincarnation coincides with science.