Grant Allen 
The Evolution of the Idea of God: An Inquiry Into the Origins of Religions [EPUB ebook] 

The Evolution of the Idea of God is a study of humans’ belief in God from primitive tribal religions to what Allen considered the more advanced Christian view. It was first published in 1897. The main question of this book is, 'How did we arrive at our knowledge of God?’ Rather than trying to prove or disprove any claims about the divine, Allen’s method simply follows the psychological processes that led humans to religious belief, and further, from a belief in polytheism to monotheism.