technically the appropriate term would be your soul or spirit is immortal...not the human vessel itself.
If you look at the world and everything in it.....there is constant patterns everywhere. birth life death exists everywhere from ideas to inventions to people to animals to plants to rocks to stars and planets. It is continous, and considering our random existence which no one can still explain with exact proof (science or religion) as to how this all came about, all we have to go by are our own perceptions and understandings of the world around us. Reincarnation basically to me doesn't sound like such a off the wall idea, especially when you do the research and it makes more sense to find out we are given free will from an omnipotent force in order to grow and develop ourselves into perfect, God like beings on earth and in various other realities. The answer to a nice perfect wonderful world is simple, the process of getting there takes much self control and understanding within each individual...and depending on how you were raised, your beliefs, personality, environment, anything can effect why you are the way you are but accepting this and changing it is different things.
I believe we cont to reincarnate on this earth or in other realities until we ourselves have felt like we are a true perfect God like being. We can decide whether to keep incarnating and teaching lessons in these different universes or we can simply live in peace and harmony in the afterlife. regardless, there is def more to this existence, whether it be God, aliens or conscious bacteria that created this existence, no one can deny we live in a pretty cray world. God gives us the answers, we just have to learn to read in between the lines and accept the fact that everybody is right in their own way, mind, and reality