Further investigation shows that these customs are not quite evenly distributed, but that certain more or less intimate associations exist between the industrial development, social organization, and religious beliefs of the peoples of the world; so that, among people with simple industries, thoughts are found that differ somewhat from those of people who have advanced further in the development of material culture. It has also been noticed that a relation exists between the ethnic life of a people and the geographical environment that favors or hinders their material development. The common cause for this similarity of actions and beliefs of peoples and tribes widely separated, belonging to different races, and being on certain stages of cultural development, has been looked for in several ways. Some investigators—like Ratzel, and in older times Karl Ritter and Guyot—have laid particular stress upon the influence of geographical environment upon the life of man, and emphasize those similarities which appear in similar types of environment. Others believe that many of the customs, beliefs, and inventions common to people who live in regions far apart are an old heritage derived from the earliest times, when mankind was still confined to a small part of the earth’s surface. Still others have tried to isolate the most generalized forms of similar ethnic phenomena. Bastian, the most important representative of this group of investigators, has called these forms “elementary ideas,” and has tried to show that they are unexplainable. Psychologists finally have endeavored to explain the similarities by an analysis of mental processes. It seems necessary to discuss these four methods of approach a little more fully.