SELECTION ON MAN. 311 



slow, for the changes in the universe are very slow ; 

 but just as these slow changes become important, when 

 we look at results after long periods of action, as we 

 do when we perceive the alterations of the earth's sur- 

 face during geological epochs; so the parallel changes 

 in animal form become more and more striking, in. 

 proportion as the time they have been going on is 

 great ; as we see when we compare our living animals 

 with those which we disentomb from each successively 

 older geological formation. 



This is, briefly, the theory of " natural selection," 

 which explains the changes in the organic world as 

 being parallel with, and in part dependent on, those in 

 the inorganic. What we now have to inquire is, 

 Can this theory be applied in any way to the question 

 of the origin of the races of man ? or is there anything 

 in human nature that takes him out of the category 

 of those organic existences, over whose successive 

 mutations it has had such powerful sway ? 



Different effects of Natural Selection on Animals and 

 on Man. 



In order to answer these questions, we must consider 

 why it is that a natural selection " acts so powerfully 

 upon animals ; and we shall, I believe, find, that its 

 effect depends mainly upon their self-dependence and 

 individual isolation. A slight injury, a temporary 

 illness, will often end in death, because it leaves the 

 individual powerless against its enemies. If an herbi- 

 vorous animal is a little sick and has not fed well for a 



