THE TIME ELEMENT. 



99 



argues, Why should not these differences 

 accumulate indefinitely by heredity, and in 

 the course of numberless successive genera- 

 tions give rise to new species ? 

 But we have shown 

 That these differences are not differences 

 in type, but merely in expression of 

 type, and are only such as must neces- 

 sarily arise from inherited differences in 

 vital force, and in conditions of exist- 

 ence, including food ; 



That these differences are strictly limited, 

 on the one hand by sterility or preco- 

 city, and on the other by death in the 

 struggle for existence. They cannot, 

 therefore, increase indefinitely ; 

 That these differences may attain their 

 maximum within two or three genera- 

 tions, and an extended period of time 

 is therefore not necessary for their full 

 development ; and 



That the maximum of these differences dis- 

 closes no tendency to specific variation. 

 The differences among individuals of the 

 same race represent only a more or less full 

 expression of the Specific life-force of that 

 race. 



Palaeontology, while it demonstrates that 

 evolution proceeded by successive steps, gives 



