io8 THEORIES OF EVOLUTION 



rupeds now upon the earth. So far as we can judge 

 of these huge forms by their skeletons, they appear to 

 have possessed a bodily structure as well fitted to survive 

 as that of many now living in the world ; but they differed 

 from these latter in that they had extremely small brains. 

 We can easily understand that inferiority of intellect 

 would cause them to be worsted by animals which were 

 in other respects no better endowed. 



Exactly parallel is the relation of man and the apes. 

 In bodily structure the difference is insignificant. In the 

 brain, however, we meet an important and essential 

 distinction. It would appear here that Natural Selection 

 has taken one particular part of the organism of paramount 

 importance in the struggle, and has developed that rather 

 than made a change along the whole line. 



We see the same relationship in the gigantic reptiles 

 of the Secondary Period as compared with the mammals 

 of the Tertiary. The latter with their larger brains and 

 higher intelligence were able to supplant the former, just 

 as they have in turn been supplanted by the still larger 

 brained animals whose descendants now people the earth. 

 All this seems to me to afford very strong support to the 

 theory of Natural Selection. 



Passing now to another class of objections : Natural 

 Selection, it is said, can never account for the beginnings 

 of things. Until an organ is raised to a useful level, 

 selection can have nothing to do with it. At first sight 

 that is a serious objection, but it suggests its own answer, 

 viz. that an organ so rarely develops ab initio. Organs 

 are not formed anew in an animal, but they are formed 

 by the modification of pre-existing organs ; so that, instead 

 of having one beginning for each organ, we have to push 

 the beginning further and further back, and find that 

 a single origin accounts for several successive organs, or 

 at any rate several functions instead of one. 



The typical vertebrate has four limbs. These in 

 fishes are used for swimming, while in terrestrial forms 

 the same limbs are modified and used for walking. New 

 organs are not introduced, but the old are modified for 

 a new purpose. When the terrestrial form again becomes 



