Why do People Believe?

[Outis]

But I believe by faith that only a higher power could have been such an excellent designer of the human body and soul.

This line of thinking, irreducible complexity, is understandable, but flawed. A counterargument would be the fact that the eyeball is a very complicated organ (one may suggest so complicated that it requires a maker), however it is actually very poorly "designed" and limited in its capabilities. I think there are better arguments to support the theory of a creator than the complexity of the human body.

What evidence do we have, outside of what religious books that were written by men say, that souls even exist?

Ultimately, this type of question will lead an individual to a different answer depending on whether one is a dualist, materialist, idealist, or something in-between.