According to v. Martius, who is a great authority on Brazilian ethnography, it is a well-established fact, observed everywhere, that the smaller and more isolated of the Indian communities, scarcely any members of which marry members of other communities, are much more liable to every kind of deterioration than the larger groups.[2026] “It is probable,” Mr. Bates, another most capable judge, remarks with reference to the savage tribes on the Upper Amazons, “that the strange inflexibility of the Indian organization, both bodily and mental, is owing to the isolation in which each small tribe has lived, and to the narrow round of life and thought, and close intermarriages for countless generations, which are the necessary results. Their fecundity is of a low degree, for it is very rare to find an Indian family having so many as four children, and we have seen how great is their liability to sickness and death on removal from place to place.”[2027] Touching the Isánna Indians, Mr. Wallace asserts that they are said not to be nearly so numerous, nor to increase so rapidly, as the Uaupés; which may perhaps be owing to their marrying with relations, while the latter prefer strangers.[2028] And v. Tschudi supposes that the low fecundity of the Botocudos is caused by their endogamous habits; for when their women marry out of their own horde, especially with whites or negroes, they are generally very fertile.[2029] The Calidonian Indians of the Isthmus of Darien, according to Mr. Gisborne, are bound never to cross the breed with foreigners; hence intermarriage is very constant, and, as he remarks, the race degenerates.[2030] The Pueblos in New Mexico, too, are said to deteriorate because of their constant intermarriage in the same village.[2031] As regards the Hottentots, Barrow remarks, “The impolitic custom of hording together in families, and of not marrying out of their own kraals, has no doubt tended to enervate this race of men, and reduced them to their present degenerated condition, which is that of a languid, listless phlegmatic people, in whom the prolific powers of nature seem to be almost exhausted.” Few of the women have more than two or three children, and many of them are barren. But this is not the case when a Hottentot woman is connected with a white man. “The fruit of such an alliance,” says Barrow, “is not only in general numerous, but they are beings of a very different nature from the Hottentot.”[2032]