IX THE HISTORY AND SCOPE OF ZOOLOGY 373 



the germ-cell and the sperm-cell, — derived from two 

 different individuals. Other mechanical disturbances 

 may assist in this production of congenital variation. 

 Whatever its causes, Darwin showed that it is all- 

 important. In some cases a pair of animals produce 

 ten million offspring, and in such a number a large 

 range of congenital variation is possible. Since on 

 the average only two of the young survive in the 

 struggle for existence to take the place of their two 

 parents, there is a selection out of the ten million 

 young, none of which are exactly alike, and the selec- 

 tion is determined in nature by the survival of the 

 congenital variety which is fittest to the conditions of 

 life. Hence there is no necessitij for an assumption 

 of the perpetuation of direct adaptations. The selec- 

 tion of the fortuitously (fortuitously, that is to say, 

 so far as the conditions of survival are concerned) pro- 

 duced varieties is sufficient, since it is ascertained that 

 they will tend to transmit those characters with which 

 they themselves were born, although it is not ascer- 

 tained that they could transmit characters acquired 

 on the way through life. A simple illustration of the 

 difference is this : a man born with four fingers only 

 on his right hand is ascertained to be likely to trans- 

 mit this peculiarity to some at least of his offspring ; 

 on the other hand, there is not the slightest ground for 

 supposing that a man who has had one finger chopped 

 off, or has even lost his arm at any period of his life, 

 will produce offspring who are defective in the slightest 

 degree in regard to fingers, hand, or arm. Darwin 

 himself, apparently influenced not merely by the 



