The word Heaven was used because that is where most of the characters in the book came from Evolution is used because the book provides a timeline of how Homo sapiens (us) might have evolved from a single-celled organism.
This science fiction story is about what God does with the souls that go to heaven and how the animals on planet Earth might have evolved into us, Homo sapiens. The latter part of the story is devoted to what we wonder about God.
Buy Heaven, Evolution, and Us by Robert L Maxwell from Australia's Online Independent Bookstore, BooksDirect.