Westermarck derived most of his materials for the study of marriage from ethnological materials. Ethnologists, students of folklore (German Völkerkunde), and archaeology are less certain than the historians of institutions whether their investigations are historical or sociological.

Jane Harrison, although she disclaims the title of sociologist, bases her conception of the origin of Greek religion on a sociological theory, the theory namely that "among primitive peoples religion reflects collective feeling and collective thinking." Dionysius, the god of the Greek mysteries, is according to her interpretation a product of the group consciousness.

The mystery-god arises out of those instincts, emotions, desires which attend and express life; but these emotions, desires, instincts, in so far as they are religious, are at the outset rather of a group than of individual consciousness.... It is a necessary and most important corollary to this doctrine, that the form taken by the divinity reflects the social structure of the group to which the divinity belongs. Dionysius is the Son of his Mother because he issues from a matrilinear group.[19]

This whole study is, in fact, merely an application of Durkheim's conception of "collective representations."

Robert H. Lowie, in his recent volume, Primitive Society, refers to "ethnologists and other historians," but at the same time asks: "What kind of an historian shall the ethnologist be?"

He answers the question by saying that, "If there are laws of social evolution, he [the ethnologist] must assuredly discover them," but at any rate, and first of all, "his duty is to ascertain the course civilization has actually followed.... To strive for the ideals of another branch of knowledge may be positively pernicious, for it can easily lead to that factitious simplification which means falsification."

In other words, ethnology, like history, seeks to tell what actually happened. It is bound to avoid abstraction, "over-simplification," and formulae, and these are the ideals of another kind of scientific procedure. As a matter of fact, however, ethnology, even when it has attempted nothing more than a description of the existing cultures of primitive peoples, their present distribution and the order of their succession, has not freed itself wholly from the influence of abstract considerations. Theoretical problems inevitably arise for the solution of which it is necessary to go to psychology and sociology. One of the questions that has arisen in the study, particularly the comparative study, of cultures is: how far any existing cultural trait is borrowed and how far it is to be regarded as of independent origin.

In the historical reconstruction of culture the phenomena of distribution play, indeed, an extraordinary part. If a trait occurs everywhere, it might veritably be the product of some universally operative social law. If it is found in a restricted number of cases, it may still have evolved through some such instrumentality acting under specific conditions that would then remain to be determined by analysis of the cultures in which the feature is embedded.... Finally, the sharers of a cultural trait may be of distinct lineage but through contact and borrowing have come to hold in common a portion of their cultures....

Since, as a matter of fact, cultural resemblances abound between peoples of diverse stock, their interpretation commonly narrows to a choice between two alternatives. Either they are due to like causes, whether these can be determined or not; or they are the result of borrowing. A predilection for one or the other explanation has lain at the bottom of much ethnological discussion in the past; and at present influential schools both in England and in continental Europe clamorously insist that all cultural parallels are due to diffusion from a single center. It is inevitable to envisage this moot-problem at the start, since uncompromising championship of either alternative has far-reaching practical consequences. For if every parallel is due to borrowing, then sociological laws, which can be inferred only from independently developing likenesses, are barred. Then the history of religion or social life or technology consists exclusively in a statement of the place of origin of beliefs, customs and implements, and a recital of their travels to different parts of the globe. On the other hand, if borrowing covers only part of the observed parallels, an explanation from like causes becomes at least the ideal goal in an investigation of the remainder.[20]

An illustration will exhibit the manner in which problems originally historical become psychological and sociological. Tyler in his Early History of Mankind has pointed out that the bellows used by the negro blacksmiths of continental Africa are of a quite different type from those used by natives of Madagascar. The bellows used by the Madagascar blacksmiths, on the other hand, are exactly like those in use by the Malays of Sumatra and in other parts of the Malay Archipelago. This indication that the natives of Madagascar are of Malay origin is in accordance with other anthropological and ethnological data in regard to these peoples, which prove the fact, now well established, that they are not of African origin.