Rafael Karsten 
The Origins of Religion [PDF ebook] 

This book, first published in 1935, collects together material on the origins of religion from two very different sources. South America, where the author spent six years studying the religious beliefs and customs of several Indian tribes representing different stages of culture; and the Finno-Ugrian area, where Finnish and Russian ethnologists had brought to light a new body of facts which formed an important addition to our knowledge of religious life at an early stage of cultural development. This book is a key work in the study of comparative religion, and is an essential reference source on the origins of religion.