A Century of Science 23 



fact that many kinds of plants and animals have 

 persisted with little or no change during several 

 successive periods, side by side with other kinds 

 in which there have been extensive variation and 

 extinction. 



In connection with this a fact of great signifi- 

 cance was elicited. Between the fauna and flora 

 of successive periods in the same geographical re- 

 gion there is apt to be a manifest family likeness, 

 indicating that the later are connected with the 

 earlier through the bonds of physical descent. It 

 was a case of this sort that attracted Darwin's 

 attention in 1835. The plants and animals of the 

 Galapagos Islands are either descended, with spe- 

 cific modifications, from those of the mainland of 

 Ecuador, or else there must have been an enor- 

 mous number of special creations. The case is one 

 which at a glance presents the notion of special 

 creations in an absurd light. But what could 

 have caused the modification ? What was wanted 

 was, to be able to point to some agency, similar to 

 agencies now in operation, and therefore intelligi- 

 ble, which could be proved to be capable of mak- 

 ing specific changes in plants and animals. Dar- 

 win's solution of the problem was so beautiful, it 

 seems now so natural and inevitable, that we may 

 be in danger of forgetting how complicated and 



