Though the causes of polyandry are thus entirely different from those of polygyny, it does not at all follow that these forms of marriage are mutually exclusive. On the contrary, they may very well exist side by side, as, indeed, they actually do in many places. But how, then, is so-called group-marriage related to these two forms? It is obviously nothing but a combination of polyandry and polygyny. In fact, whenever a group of men marries a group of women, these two forms of polygamy are both involved. Every man has several wives, and every wife has several husbands. Only, indeed, on the basis of a purely external and superficial consideration could one look upon polygyny and polyandry as unconjoinable, because they are, in a certain sense, opposing ideas. As a matter of fact, they do not really exclude each other. If we bear in mind the causes mentioned above, it is obvious that under certain conditions of life, such as occur particularly in a more primitive environment, their combination is more probable than their mutual exclusion. If, especially among tribes who have not yet developed sharply defined distinctions based on property and power, as, for example, among the Australians, every man strives to obtain several wives (which is the state of polygyny), while, on the other hand, there actually exists a dearth of women (which means that motives to polyandry are present), the two forms naturally combine with each other. This is frequently verified, moreover, whenever we are able to gain any degree of insight into the particular conditions surrounding the origin of such group-marriages, and also whenever their forms undergo a modification of details. Among Australian tribes, for example, particularly in the southern part of the continent, there is a common form of group-marriage, in which a man possesses either one or several chief wives, together with secondary wives; the latter are the chief wives of other men, whereas his own chief wife is in turn the secondary wife of those men or of others. This custom is very similar to what is probably the most common form of polygyny, namely, the possession by a man of only _one_ chief wife in addition to several secondary wives,--a form of marriage that is obviously derived from monogamy. One agency that is particularly apt to bring about such a form of marriage, transitional between monogamy and polygyny, is war. We know from the Iliad that in barbaric times woman was the booty of the conqueror, and became his slave or secondary wife. So also, according to the Biblical legend, Abraham possessed a chief wife, Sarah, who belonged to his own tribe, but also a secondary wife, Hagar, who was an Egyptian slave. Wherever the concept of property became prominent, the purchase of women proved to be a further source of polygyny. In this case also, there was generally _one_ chief wife, wherever polyandry did not interfere. When the Mohammedan of modern