[395] On sterility as the result of crossing in species, see WALLACE, _Darwinism_, 152-86; DARWIN, _Animals and Plants under Domestication_, II, 78 ff.; and on the good effects of crossing and the evil effects of close interbreeding, _ibid._, II, 92-126, 104. _Cf._ QUATERFAGES, _The Human Species_, 85-88 (crossing species), 276-86 (effects of crossing in mixed races); MITCHELL, "Blood-Relationship in Marriage," in _Memoirs of London Anth. Society_, 1865, II, 402-56; and WITHINGTON, _Consanguineous Marriages_, 2 ff., who believes the injurious effects of such unions on the offspring have been overestimated. On the other hand, it has been maintained that under primitive conditions the advantages of close intermarriage may have outweighed all disadvantages: _Mucke_, _Horde und Familie_, 245-47, combating Westermarck's view. [396] DARWIN, _Effects of Cross and Self-Fertilization in the Vegetable Kingdom_, 436. [397] CUNOW, _Australneger_, 184 ff., rejects Westermarck's theory, first, on the ground that the prohibition of intermarriage in the cases cited often extends far beyond the local group; and secondly, because where the members of a _gens_ do not at the same time form a local community, marriage is not forbidden in the group of persons actually living together. But Westermarck is dealing with origins; and he does not mean to say that all the existing complex systems of kinship which have gradually been developed through association of ideas or other influences actually now conform to the principle for which he contends. On the other hand HELLWALD, _Die mensch. Familie_, 178 ff., following WAGNER, in _Kosmos_, 1886, I, 21, 24-34, reaches a conclusion essentially like that obtained by Westermarck. He finds the origin of exogamy in a dread of close intermarriage producing a horror of incest. During the period of the endogamous mother-group such marriages were the rule. With the rise of fixed habitations for the group, beginning in the glacial age and carried farther in the diluvial period, came more permanent sexual relations, the prototype of real marriage. This close living together, because of its deadening effect on sexual attraction, produced a dislike of unions in the group, leading to exogamy, often accompanied by wife-capture; although neither rape nor exogamy must be regarded as a universal stage of social evolution. CRAWLEY, _Mystic Rose_, 222, 223, 443 ff., rejects Westermarck's theory of a general human "instinct" against inbreeding. He insists that neither incest nor promiscuity was "ever anything but the rarest exception in any stage of human culture, even the earliest; the former being prevented by the psychological difficulty with which love comes into play between persons either closely associated or strictly separated before the age of puberty, a difficulty enhanced by the ideas of sexual taboo, which are intensified in