When two races of men meet they act precisely like two species of animals,—they fight, eat each other, bring diseases to each other &c., but then comes the more deadly struggle, namely which have the best fitted organizations, or instincts (ie intellect in man) to gain the day…. Man acts on & is acted on by the organic and inorganic agents of this earth like every other animal.
Notebook E, 63, 65
I suspect that a sort of sexual selection has been the most powerful means of changing the races of man. I can shew that the difft races have a widely difft standard of beauty. Among savages the most powerful men will have the pick of the women & they will generally leave the most descendants.
Darwin to A. R. Wallace,
28 [May 1864], DCP 4510
Probably you are right on all the points you touch on except as I think about sexual selection which I will not give up…. It is an awful stretcher to believe that a Peacock’s tail was thus formed, but believing it, I believe in the same principle somewhat modified applied to man.
Darwin to A. R. Wallace,
15 June [1864], DCP 4535
Man tends to multiply at so rapid a rate that his offspring are necessarily exposed to a struggle for existence, and consequently to natural selection. He has given rise to many races, some of which are so different that they have often been ranked by naturalists as distinct species.
Descent 1871, vol. 1, 185
Although the existing races of man differ in many respects, as in colour, hair, shape of skull, proportions of the body, &c., yet if their whole organisation be taken into consideration they are found to resemble each other closely in a multitude of points.
Descent 1871, vol. 1, 231–32
The belief that there exists in man some close relation between the size of the brain and the development of the intellectual faculties is supported by the comparison of the skulls of savage and civilised races, of ancient and modern people.
Descent 1871, vol. 1, 145
I do not intend to assert that sexual selection will account for all the differences between the races.
Descent 1871, vol. 1, 249
The strongest and most vigorous men,—those who could best defend and hunt for their families, and during later times the chiefs or head-men,—those who were provided with the best weapons and who possessed the most property, such as a larger number of dogs or other animals, would have succeeded in rearing a greater average number of offspring, than would the weaker, poorer and lower members of the same tribes. There can, also, be no doubt that such men would generally have been able to select the more attractive women.
Descent 1871, vol. 2, 368–69
It would be an inexplicable circumstance, if the selection of the more attractive women by the more powerful men of each tribe, who would rear on an average a greater number of children, did not after the lapse of many generations modify to a certain extent the character of the tribe.
Descent 1871, vol. 2, 369