MR. G. J. ROMANES ON PHYSIOLOGICAL SELECTION. 339 



both plants and animals. To all these criticisms Darwin replies 

 in the last editions of his works*, with what degree of success 

 I will presently consider. 



3rd. The third and last difficulty which I have to mention 

 consists in the swamping influence upon an incipient variety of 

 free intercrossing. This difficulty was first prominently an- 

 nounced in an anonymous essay by the late Professor Pleemiug 

 Jenkin of Edinburgh, published in the ' North British Eeview ' 

 for 1867 1. If to this difficulty we add the consideration adduced 



* See ' Origin of Species,' ed. 6, pp. 166-1 57 and 169-176. ' Variation ' &c. ii. 

 pp. 211-219. And as to Instincts, ' Mental Erolution in Animals,' pp. 378-379. 



t This article is in all respects a highly remarkable one, and, for the space 

 it covers, presents more searching and effective criticism of Mr. Darwin's theory 

 than any other essay with which I am acquainted. With regard to this par- 

 ticular difficulty from the swamping effects of intercrossing, the criticism is 

 especially cogent, and, so far as I know, is the only criticism of importance 

 which Mr. Darwin has not expressly answered. Without reproducing all the 

 numerical calculations wherewith the author sustains this criticism, it will here 

 be enough to quote one of his illustrations : — 



" Suppose a white man to have been wrecked on an island inhabited by 

 negroes, and to have established himself in friendly relations with a powerful 

 tribe whose customs he has learnt. Suppose him to possess the physical 

 strength, energy, and ability of a dominant white race, and let the food and 

 climate of the island suit his constitution ; grant him every advantage which we 

 can conceive a white to possess over the native ; concede that in the struggle 

 for existence his chance of a long life will be much superior to that of the 

 native cliiefs. Yet from all these' admissions there does not follow the conclu- 

 sion that after a limited or unlimited number of generations the inhabitants of 

 the island will be white. Our shipwrecked hero would probably become king ; 

 he would kill a great many blacks in the struggle for existence ; he would have 

 a great many wives and children, while many of his subjects would live and 

 die as bachelors ; an insurance company would accept his life at perhaps one 

 tenth of the premium which they would exact from the most favoured of the 

 negroes. Our white's qualities would certainly tend very much to preserve him 

 to a good old age ; and yet he would not suffice in any number of generations 

 to turn his subjects' descendants white. It may be said that the white colour ■ 

 is not the cause of the superiority. True ; but it may be used simply to bring 

 before the senses the way in which qualities belonging to one individual in a large 

 number must be gradually obliterated. In the first generation there will be 

 some dozens of intelligent young mulattoes, much superior in average intelli- 

 gence to the negroes. We might expect the throne for some generations to be 

 occupied by a more or less yellow king ; but can any one believe that the whole 

 island will gradually acquire a white or even a yellow population, or that the 

 islanders would acquire the energy, courage, ingenuity, patience, self-control, 

 endurance, in virtue of which qualities our hero killed so many of their 



27* 



