Over-population ^^5 



Another assumption which Darwin made was that va- 

 riation from type must of itself bring the individual some 

 advantage or disadvantage. It stands to reason that if two 

 things are not alike one must be better than the other. This 

 is so " reasonable " that it is difficult for most of us to 

 see that it is not true, We cannot hold this against 

 Darwin when we realize that hardly any of us today can 

 compare human beings without making invidious impli- 

 cations. 



Over -population 



The number of eggs or seeds produced by any living spe- 

 cies is far in excess of what the environment can maintain as 

 completed individuals. A large part of the food accumulated 

 by a plant, for example, is converted into reserve for the 

 embryo of the next generation. A large part of the food 

 accumulated by a fish goes to the making of eggs. Con- 

 versely, a large part of the food consumed by plants as well 

 as by animals is taken directly from the bodies of other living 

 things. Eggs and seeds are particularly attractive as food for 

 members of other species. 



Darwin himself made a calculation to show the im- 

 portance of geometrical increase even in such a slowly breed- 

 ing species as the elephant. Suppose that the elephants 

 begin breeding at thirty years of age and continue to ninety 

 years, producing in the interval six young, and that each 

 survives to the age of one hundred years. These are all very 

 conservative estimates. There would then be living after 

 740 to 750 years nineteen million descendants of a single 

 pair. Smaller animals breed much more rapidly and the 

 ratio of fertilized eg^ or seed to surviving adult will in some 

 species be well over a million. Dr. Punnett had occasion to 

 study some rotifers, microscopic animals, through sixty- 

 seven generations. Allowing an average of thirty eggs 

 for each reproduction, he showed that if every individual 

 were allowed to live out its life and reproduce, there 



