42 GENETIC VARIATIONS 



uent atoms so as to yield a chemically and physiologically 

 altered material. Thus an essentially new gene is held 

 to be produced, yielding new characteristics, structural or 

 physiological. 



Such change in the constitution of the genes would appear 

 to constitute the primary and fundamental type of genetic 

 variation. Without it, recombination of genes appears power- 

 less to produce effects, for without it there are no diverse 

 kinds of genes to recombine. If the changes in gene material 

 are of appropriate character, they supply the remaining factor 

 that is logically necessary for understanding evolutionary 

 change. The transmutation, or "mutation," of the genie mate- 

 rials, will, if it is of appropriate nature, supply new unit genes. 

 Biparental reproduction shuffles and recombines the different 

 genes so produced, giving organisms with diverse combina- 

 tions of characteristics, on which selective survival and elimi- 

 nation may act. New lasting groupings of the genes may be 

 given by irregularities in the operation of the genetic system 

 that we have before described. Thus with mutations of appro- 

 priate character, there is logically a complete scheme for 

 evolution that will yield both adaptation and progress. 



But the fundamental question remains: Are the observed 

 changes of genes indeed of such a nature as will yield progres- 

 sive evolution? With that question in mind, we proceed to 

 an examination of the changes in genie materials that are 

 known as gene mutations. (We shall follow common usage 

 in employing the term gene mutation, although on later 

 pages its appropriateness as a designation will be called in 

 question.) 



In practice, for a change in the inherited characteristics to 

 be identified as a gene mutation, certain conditions must be 

 fulfilled. It must be possible to show that the change is not the 

 result of ordinary recombinations, such as occur in Mendelian 



