[289] ‘Transact. B. Soc. of Edinburgh,’ vol. xxii. 1861, p. 567.
[290] ‘On the Phenomena of Hybridity in the Genus Homo,’ Eng. translat. 1864.
[291] See the interesting letter by Mr. T. A. Murray, in the ‘Anthropolog. Review,’ April, 1868, p. liii. In this letter Count Strzelecki’s statement, that Australian women who have borne children to a white man are afterwards sterile with their own race, is disproved. M. A. de Quatrefages has also collected (‘Revue des Cours Scientifiques,’ March, 1869, p. 239) much evidence that Australians and Europeans are not sterile when crossed.
[292] ‘An Examination of Prof. Agassiz’s Sketch of the Nat. Provinces of the Animal World,’ Charleston, 1855, p. 44.
[293] ‘Military and Anthropolog. Statistics of American Soldiers,’ by B. A. Gould, 1869, p. 319.
[294] ‘The Variation of Animals and Plants under Domestication,’ vol. ii. p. 109. I may here remind the reader that the sterility of species when crossed is not a specially-acquired quality; but, like the incapacity of certain trees to be grafted together, is incidental on other acquired differences. The nature of these differences is unknown, but they relate more especially to the reproductive system, and much less to external structure or to ordinary differences in constitution. One important element in the sterility of crossed species apparently lies in one or both having been long habituated to fixed conditions; for we know that changed conditions have a special influence on the reproductive system, and we have good reason to believe (as before remarked) that the fluctuating conditions of domestication tend to eliminate that sterility which is so general with species in a natural state when crossed. It has elsewhere been shewn by me (ibid. vol. ii. p. 185, and ‘Origin of Species,’ 5th edit. p. 317) that the sterility of crossed species has not been acquired through natural selection: we can see that when two forms have already been rendered very sterile, it is scarcely possible that their sterility should be augmented by the preservation or survival of the more and more sterile individuals; for as the sterility increases fewer and fewer offspring will be produced from which to breed, and at last only single individuals will be produced, at the rarest intervals. But there is even a higher grade of sterility than this. Both Gärtner and Kölreuter have proved that in genera of plants including numerous species, a series can be formed from species which when crossed yield fewer and fewer seeds, to species which never produce a single seed, but yet are affected by the pollen of the other species, for the germen swells. It is here manifestly impossible to select the more sterile individuals, which have already ceased to yield seeds; so that the acme of sterility, when the germen alone is affected, cannot be gained through selection. This acme, and no doubt the other grades of sterility, are the incidental results of certain unknown differences in the constitution of the reproductive system of the species which are crossed.
[295] ‘The Variation of Animals,’ &c., vol. ii. p. 92.
[296] M. de Quatrefages has given (‘Anthropolog. Review,’ Jan. 1869, p. 22) an interesting account of the success and energy of the Paulistas in Brazil, who are a much crossed race of Portuguese and Indians, with a mixture of the blood of other races.
[297] For instance with the aborigines of America and Australia. Prof. Huxley says (‘Transact. Internat. Congress of Prehist. Arch.’ 1868. p. 105) that the skulls of many South Germans and Swiss are “as short and as broad as those of the Tartars,” &c.
[298] See a good discussion on this subject in Waitz, ‘Introduct. to Anthropology,’ Eng. translat. 1863, p. 198-208, 227. I have taken some of the above statements from H. Tuttle’s ‘Origin and Antiquity of Physical Man,’ Boston, 1866, p. 35.