CREATION BY EVOLUTION 



other vertebrates had until then not been able to conquer. 

 Such changes, involving the improvement of the all-round 

 achievements of the organism without depriving it of valu- 

 able possibilities, may properly be called biological progress. 

 They are simply examples of specialization that is not one- 

 sided, but balanced. 



We may take one further example, which brings out the 

 difference between the two processes. The most primitive 

 members of the group to which we and all other backboned 

 animals belong — forms like Amphioxus, for instance — have 

 no true eye, have probably only a very slight sense of smell 

 (certainly no nasal organ of our type), and no ear. The 

 lower vertebrates, such as the fishes, have very efficient sight 

 and smell but practically no sense of hearing. Both birds 

 and mammals (in general) have acute hearing and much 

 improved sight. Here there is a real biological advance; 

 the efficiency of all three senses has enormously improved, 

 and improved in a balanced way, in passing from Amphioxus 

 to higher vertebrate. But in this same field we may find 

 unbalanced improvement, one-sided specialization. The 

 improvement in the utilization of the sense of sight, which 

 is so obvicfus in the whole group of monkeys and apes and 

 culminates in man, has been accompanied by a degeneration 

 in the power of smell ; the same has been true in many birds, 

 which also rely almost entirely upon sight. On the other 

 hand, the mole relies almost entirely upon touch and hear- 

 ing, and its eyes have degenerated. Thus in all these forms 

 an unbalanced improvement in one direction has led to a 

 cutting down of faculty in another. 



The main improvements of life during its evolution must 

 obviously be improvements of the balanced type, not mere 

 specializations, since it seems certain that no highly special- 

 ized animal or plant has ever succeeded in becoming the 



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