THE CHANGING WORLD OF LIFE 551^ 



We should not close this discussion of mutations without mentioning 

 one of the most important phases of it — a phase which greatly concerns 

 all of us in this atomic age. High energy radiations, such as X-rays, 

 radium, and the neutron radiation from the products of atomic fission, 

 can increase the rate of mutation. Since most mutations are likely to 

 be harmful to the persons who express them, it is possible that mass ex- 

 posure of large numbers of people to radiation from atomic or hydrogen 

 bombs can result in harmful changes in the genes of heredity. (The 

 amount of radiation received in routine X-ray pictures is too small to 

 be of great consequence in this connection.) In natural and artificial 

 selection the harmful mutations are gradually eliminated from a species, 

 but in man we try to save all of those born regardless of any defects 

 which may be present. An excessive number of mutations can thus 

 weaken an entire race. All too often, we concentrate on the damage 

 which may be done to individuals by the explosion of these new bombs, 

 but we might well be concerned about their effects on the germ plasm 

 which will carry on into the future. 



Biological Evolution 



The constant changing of living things which takes place as a result 

 of mutations coupled with selection is known as biological or organic 

 evolution as distinguished from cosmic, geographical, and other forms of 

 evolution. That these changes have occurred in the past and are now 

 occurring is a definitely established fact which anyone can verify who 

 will take the trouble to investigate the evidence available. The full ex- 

 tent of these changes, however, is open to question and probably can 

 never be settled absolutely, since the evidence is incomplete and of a 

 circumstantial nature. 



However, since life has existed on the earth for quite a few million 

 years, it seems that evolution has been quite extensive. There was an 

 unfortunate confusion of the facts and theories of evolution with re- 

 ligious issues at a time in the past that caused misunderstandings on the 

 subject. Today, most thinking people realize that the exact method of 

 creation of plant and animal life is a scientific and not a religious ques- 

 tion. There is nothing in the evolutionary concept that could weaken 

 one's religious belief. If we will free our minds of any prejudice in 

 this connection and examine some of the evidences of evolution, we can 

 gain some insight into the possible extent to which it has taken place. 



Evidence from Embryology. A study of embryonic development of 

 animals often gives us valuable information concerning the evolutionary 

 relationships with other animals. The lamprey eel as an adult is quite 



