[273] Among the aborigines of New Britain, according to POWELL, _Unter den Kannibalen von Neubritannien_, 123; and among the Lacondou Indians of Central America, according to CHARNAY, _Les anciennes villes du nouveau monde_, 399. "Negro women of unmixed blood seldom have voluptuous figures, and in anatomical structure they resemble the men in a remarkable way, so that seen from a distance they are scarcely to be distinguished from them. The same is true for a whole series of low races."--HELLWALD, _op. cit._, 6. [274] "Bedenken wir die vielen Mittel, die gerade die Civilisation hierzu bietet, so dürfte dem befremdenden Urteile nicht mehr zu widersprechen sein, dass bei wirklichen Naturvölkern und unter normalen sozialen Verhältnissen der erotische Antrieb ein beschränkterer sei, als auf höheren Stufen der Civilisation."--LIPPERT, _Geschichte der Familie_, 29, 30. Among the highly civilized of our own times the nervous system is very greatly developed, and therewith the capacity for sexual pleasure is proportionately increased; see HELLWALD, _op. cit._, 11 ff., 128, and the literature there cited. The lives of the lower animals reveal a great variety of sexual relations. The lowest form, and perhaps the most frequent, is that of unlimited promiscuity.[275] Among the invertebrates the preservation of the young is left almost wholly to chance. The duties of the parents are limited mainly to the functions of reproduction. "In the lowest classes of vertebrata, parental care is likewise almost unheard of." It "rarely happens that both parents jointly take care of their progeny."[276] But the chelonia, or tortoise group, are "known to live in pairs;" and here we reach, among animals, the first trace of the family, properly so called. "The chelonia form, with regard to their domestic habits, a transition to the birds, as they do also from a zoölogical and, particularly, from an embryological point of view." Who that has experienced the keen delight afforded by watching the domestic habits of birds, from the building of the nest to the teaching of the young to make the first wavering trial of its wings, cannot bear witness to the high development of marriage and the family among them? The great work of Brehm supplies abundant evidence of their human-like social life.[277] "Parental affection," summarizes Westermarck, "has reached a very high degree of development, not only on the mother's side, but also on the father's. Male and female help each other to build the nest, the former generally bringing the materials, the latter doing the work. In fulfilling the numberless duties of the breeding season both birds take a share. Incubation rests principally with the mother, but the father, as a rule, helps his companion, taking her place when she wants to leave the nest for a moment, or providing her with food and protecting her from every danger. Finally, when the duties of the breeding season are