STRUCTURE OF THE BRAIN 263 



there remains one important agency, namely Sexual Selec- 

 tion, which appears to have acted powerfully on man, as on 

 many other animals. I do not intend to assert that sexual 

 selection will account for all the differences between the 

 races. An unexplained residuum is left, about which we 

 can only say, in our ignorance, that as individuals are con- 

 tinually born with, for instance, heads a little rounder or 

 narrower, and with noses a little longer or shorter, such slight 

 differences might become fixed and uniform, if the unknown 

 agencies which induced them were to act in a more constant 

 manner, aided by long-continued intercrossing. Such varia- 

 tions come under the provisional class alluded to in our sec- 

 ond chapter, which for the want of a better term are often 

 called spontaneous. Nor do I pretend that the effects of 

 sexual selection can be indicated with scientific precision; 

 but it can be shown that it would be an inexplicable fact if 

 man had not been modified by this agency, which appears 

 to have acted powerfully on innumerable animals. It can 

 further be shown that the differences between the races of 

 man, as in color, hairiness, form of features, etc., are of a 

 kind which might have been expected to come under the 

 influence of sexuaV selection. But in order to treat this sub- 

 ject properly, I have found it necessary to pass the whole 

 animal kingdom in review. I have therefore devoted to it 

 the Second Part of this work. At the close I shall return 

 to man, and, after attempting to show how far he has been 

 modified through sexual selection, will give a brief summary 

 of the chapters in this First Part. 



Note on the Eesemblances and Differences in the 

 Steuotuee and the Development of the Brain 

 IN Man and Apes. Bt Peof. Huxley, F.E.S. 



The controversy respecting the nature and the extent of 

 the differences in the structure of the brain, in man and the 

 apes, which arose some fifteen years ago, has not yet come 

 to an end, though the subject-matter of the dispute is, at 



