4 EVOLUTION AND MAN S PLACE IN NATURE 



If only this implication be recognised, that the 

 origin of life lies behind its evolution, we need not 

 linger to conjecture how many primordial forms it 

 may be necessary to admit, nor need we inquire as 

 to the history of the appearance of these. Specu 

 lative questions may be left in abeyance for the 

 present. They will assert themselves in good time, 

 though they are held in reserve^at this early stage. 

 For commencement, we are restricted to the history 

 of the existing. Afterwards, speculative thought may 

 claim its rights. 



Granting that Evolution supplies the key to a large 

 part of the natural history of life on the earth, pro 

 gress has not been by a single grand movement, as 

 when the tidal wave rises in the ocean, or as when 

 the course of the river has been determined by the 

 configuration of the valley. The law of Evolution has, 

 indeed, had constant application, but it has not 

 worked precisely the same results in all cases. En 

 vironment has presented varying conditions, and the 

 consequence has been endless diversity in the history 

 of life itself. The laws providing for evolution have, 

 however, operated so constantly, that we should not 

 seriously err, if we were to depict the history of life as 

 a unity, representing a constant and world-wide pro 

 gress. Still, adaptation to environment has been 

 fruitful of varieties. Though the struggle for exist 

 ence has not been by any means uniform, it has 

 been sufficiently general to rank as a formative cause. 

 Exact estimates of its efficiency will bring us to re 

 stricted areas of food-supply, or areas more or less 

 crowded with competitors ; but the struggle does not 

 disappear even when food is abundant, and demand 



