The great variation in the extent of prohibited degrees found among nations is "nearly connected with their close living together." Savage and barbarous peoples, "if they have not remained in the most primitive social condition of man, live, not in separate families, but in large households or communities, all the members of which dwell in very close contact with each other." Such are the house-communities of the American aborigines, found everywhere, from the "long houses" of the Iroquois to the vast pueblos or "cities" of Mexico and Yucatan;[389] the "joint undivided families" of the Hindus and Southern Slavs;[390] and the _trevs_ or clan households of ancient Wales, comprising four generations living in one inclosure, whose members are forbidden to intermarry.[391] It is significant that in all such cases we find extended prohibitions of close intermarriage, which do not exist "where the family lives more separately." In fact, there is a marked tendency, amounting almost to a law, that the larger the family or clan group, the wider is the circle of forbidden degrees; and, on the contrary, the more isolated and dispersed the manner of life, the greater is the liberty of matrimonial choice.[392] [389] MORGAN, _Houses and House-Life of the American Aborigines_; FISKE, _Discovery of America_, I, 64 ff.; WESTERMARCK, _op. cit._, 324. [390] MAINE, _Early History of Institutions_, 7, 78, 106, 195, 200, _passim_; _Early Law and Custom_, chap, viii; KRAUSS, _Sitte und Brauch der Südslaven_, 14, 64, 72, 79 ff., 84, etc.; KOHLER, "Indisches Ehe- und Familienrecht," _ZVR._, III, 362; _cf._ LYALL, _Asiatic Studies_, chap. vii. [391] LEWIS, _Ancient Laws of Wales_, 56, 57, 196. [392] _Westermarck_, _op. cit._, 323-28. In the same way prohibition of marriage on the ground of "affinity" or "spiritual relationship" may take place. "By association of ideas" the "feeling that two persons are intimately connected in some way" may "give rise to the notion that marriage or intercourse between them is incestuous." A strong argument is also derived from the "classificatory system of consanguinity." Tylor has shown that this system and the system of exogamy are, in most cases, found together. They are the "two sides of one institution."[393] [393] TYLOR, _On a Method of Investigating the Development of Institutions_, 261 ff.; _cf._ WESTERMARCK, _op. cit._, 328, 329.