FIVE LINKS TO THE CHAIN 59 



on the earth as has never been dreamed of heretofore. Swarm- 

 ing millions of creatures would, within a few days, crowd out 

 of sight even the standing space of the earth. Soon after- 

 ward the food supply of the world would be used up, and 

 starvation would face all save those who found it possible 

 to support their own lives by taking other lives. 



This is no fancy picture. It would be the inevitable state 

 of things if the prodigality of nature were not checked some- 

 how. Fortunately there are checks on every side. Wind and 

 weather, flood and fire; take part in limiting the numbers of 

 those that are to survive for a next generation. For the 

 struggle is not simply between the individuals themselves 

 but also between each individual and its surroundings. Clearly 

 enough, then, the maimed, the weak, and the inefficient gen- 

 erally have the poorest chance to live and become ancestors. 

 And it is just because they do not live long enough to be- 

 come ancestors that the race escapes deterioration. On every 

 side they are crowded out in the struggle. 



III. VARIATION 



This fact brings us face to face with the third link in Dar- 

 win's chain. He noticed that while some animals of a species, 

 are large, others of the same species are small ; where some 

 are strong, others are weak ; where some have keen intelli- 

 gence, others are slow of understanding. He saw that always 

 and everywhere, among all kinds of plants and animals, there 

 are contrasts, differences, and variations. On this fact he 

 based what he called the law of variation. It is the third 

 link in Darwin's chain. Follow it now somewhat in detail. 



When rain was withheld for some months in South Amer- 

 ica, Darwin saw thousands of animals die for lack of water ; 

 yet there is such variety in the power of animals to endure 



