36 evolution: the ages and tomorrow 



present, are themselves undergoing random changes— muta- 

 tions which may or may not be of use and benefit to the 

 organism. Trial and error characterize this situation, not 

 intelligent direction from within or without. The organism 

 is the sum total of its genes and reacts to the limiting en- 

 vironment in which it finds itself as the genes dictate. If the 

 hereditary control is a happy one, the organism will enjoy 

 the protection of the Darwinian selection; if the heredity is 

 an unhappy combination, ultimate extinction is its fate. 

 There is, then, a two-factor process at work here: the genes 

 which are associated to form an organism; and the environ- 

 ment which will determine, not only survival, but the de- 

 gree of success. The meaning of these blind selective forces 

 in the evolution of mind-matter will be examined later; for 

 the present, the character and behavior of the genes are of 

 interest. 



The physical basis of heredity, and hence of evolution, is 

 the chromosome and its complex of genes. The mechanism 

 is flexible in that it undergoes changes at the same time that 

 it offers relative stability. There is no evidence whatever 

 for any other mechanism. It is true that genetics, the science 

 of the genes, has not solved all the problems that crop up in 

 a study of the evolutionary process; but it has made a dis- 

 tinct and very definite beginning. In the first place the 

 thread-like bodies we call the chromosomes, which are car- 

 ried in all cells, are classifiable in the usual sense of the term 

 "reality"; the brick and stone buildings in which we live 

 are no more real. These chromosomes are the only living 

 bond between parent and offspring, whatever the kinds of 

 organisms. This we know for a certainty. The genes are 

 arranged in single file on the threads of the chromosomes, 

 and the whole mechanism is distributed with great qualita- 

 tive and quantitative accuracy to the daughter cells of any 

 division. Many high school and college students have been 

 shown or have studied with the microscope the divisions and 

 distribution of the chromosomes. The theory of the gene is 



