122 DOCTRINE OF EVOLUTION 



species, as we may see more clearly at a later juncture, 

 but the essential point here is that they are not un- 

 real, although they may not as yet be described by 

 science in final analytical terms. 



We come now to the second element of the whole 

 process of evolution, namely, what we may call over- 

 production or excessive multiplication. Like varia- 

 tion and so many other phenomena of nature, this is 

 so real and natural that it escapes our attention until 

 science places it before us in a new light. The normal 

 rate of reproduction in all species of animals is such 

 that if it were unchecked, any kind of organism would 

 cumber the earth or fill the sea in a relatively short 

 time. That this is universally true is apparent from 

 any illustration that might be selected. Let us take 

 the case of a plant that lives for a single year, and that 

 produces two seeds before it withers and dies; let us 

 suppose that each of these seeds produces an adult 

 plant which in its turn lives one year and forms two 

 seeds. If this process should continue without any 

 interference, the twentieth generation after as many 

 years would consist of more than one million descen- 

 dants of the original two-seeded annual plant, pro- 

 vided only that each individual of the intervening 

 years should live a normal life and should multiply 

 at the natural rate. But such a result as this is rendered 

 impossible by the very nature which makes annual 

 plants multiply in the way they do. Let us take the 

 case of a pair of birds which produce four young in 

 each of four seasons. Few would be prepared for the 



