COSMIC PHILOSOPHY 



enormous. If a grain of sand were each year 

 added to an ant-heap, it would in course of time 

 become as large as Chimborazo. But these 

 changes, directly caused by natural selection, 

 are greatly aided and emphasized by other 

 changes indirectly produced by correlation of 

 growth, and also by what is called the law of 

 use and disuse. By correlation of growth, or 

 internal equilibration, we mean the effect pro- 

 duced upon any part of the organism by change 

 in a related or neighbouring part. Let us sup- 

 pose that it becomes advantageous to some 

 feHne animal, like the ancestor of the lion, to 

 have large and powerful jaws. Since no two 

 of our leonines would have jaws of exactly the 

 same size and strength, natural selection would 

 preserve all the strong-jawed individuals, while 

 the weak-jawed individuals would succumb in 

 the struggle for life. In the course of many 

 generations our race of leonines would possess 

 on the average much larger and stronger jaws 

 than at the period at which we began to con- 

 sider it. But greater weight of jaw entails in- 

 creased exertion of the muscles which move the 

 jaw, so that these muscles, receiving more and 

 more blood, will become permanently increased 

 in size and power. The portions of the skull 

 into which the jaw bones fit will likewise receive 

 an extra strain, and will consequently increase 

 in rate of nutrition and grow to a larger size, so 



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