Chap. 38 ORGANIC evolution — conservation 787 



Mutations. Evolutionary changes consist of changes in heredity. Mutations 

 are probably pre-eminent among them. They are sudden inheritable charac- 

 teristics caused by changes in genes, the chemical units of the chromosomes. 

 Mutations are discussed elsewhere (Chap. 20). This note is given here in view 

 of their place in evolution. Probably all genes mutate at some time; some of 

 them much oftener than others. Their frequency may be changed experi- 

 mentally, and also in nature, by heat, radiation, and other influences. Muta- 

 tions differ in extent; they may be "large," those having the greatest effect on 

 the animal, such as brittle bones in man, or they may be "small" such as nar- 

 row nostrils in man. The effects of mutations of the genes have no evident 

 relationship to the adaptation of the animal. They appear to be random 

 changes. This is true of experimental mutations; those caused by applications 

 of heat have no relation to adaptation to the temperature of the environment. 

 For an animal that is not well adapted to its life in a certain place, some ran- 

 dom mutation, however, might be the very one that would improve matters. 



Evolution and the Kinships of Animals and Man 



By many evidences, it is clear that all protoplasm has the same basic organi- 

 zation, and that all living things that exist or have existed are related including 

 man. 



Humanity is bound to other animals by many and deep kinships. Neverthe- 

 less man is unique among all animals, in flexibility of behavior, in control of 

 the environment, in social organization, in degree of reasoning power, and in 

 other qualities of mind and its expression. 



Humanity is unique in having two inheritances that are highly different, yet 

 blend on their borders. One of them is concerned with organic evolution, with 

 features such as the build and grip of the hand, the size and activity of the 

 brain. The other is a newer kind of social evolution built on cultures passed 

 on by legends and records even through long lapses of time (Fig. 38.8). Past 

 experiences are preserved, available for help and warning. The records of them 

 have accumulated greatly and constitute a complex story of ups and downs of 

 human thought and deed. Human beings alone are aware of their own evolu- 

 tion and their possible ability to direct it. In order to do so, they must use their 

 double inheritance especially that of experience in which at sometime ethics 

 appeared. 



Separate Creations 



The first time a puppy sees a strange animal in the grass he shies back. Then, 

 curiosity overcomes him and he goes closer. From earliest times, human beings 

 have been afraid of things. But, as with the puppy curiosity has prevailed; 

 mankind has drawn closer, inquired and tried to explain. 



In the sixth, fifth, and fourth centuries B.C., Aristotle and other Greek 



