ao THE DARWINIAN THEORY 



periods or ages of exactly the same kind as that 

 which exists between the men of successive genera- 

 tions or centuries — viz., a blood relationship. Just 

 as men of each century are descendants of those of 

 a preceding century, and progenitors of those of later 

 ones, so it is with animals throughout all geologic 

 history. 



It is well to point out clearly the difficulty which 

 has to be met. Animals of successive ages are 

 unlike, and fossils do not give the intermediate 

 series, nor satisfactory indications of them. The 

 problem we have to consider is this : The men of 

 successive generations are unlike in language, cus- 

 toms, dress, and appearance ; now, are the differences 

 between animals of successive ages of the same 

 character as between men, though of wider nature ; 

 or are they of such a kind as to forbid the idea of 

 descent one from another ? In other words, are 

 species immutable or variable ? The doctrine of 

 Evolution requires that they should be variable. In 

 order to establish this doctrine it must be shown 

 that there are causes, actually existent causes, com- 

 petent to give rise to modifications of animals such 

 as we find in passing from one geologic age to 

 another. This is what is effected by the " Dar- 

 winian Theory," or the " Theory of Natural Selec- 

 tion," propounded independently and simultaneously 

 on July i, 1858, by Darwin and Wallace. 



Charles Darwin was born in 1 809, and studied 

 at Cambridge from 1827 to 1831. The voyage of 

 the Beagle occupied from 183 1 to 1836, the greater 

 part of the time being spent on the east and west 



