NEW COMBINATIONS OF GENES 19 



new combinations of characteristics. Every combination of 

 genes that is mathematically conceivable may thus be pro- 

 duced. Every possible combination of the characteristics that 

 depend on the genes may thus be brought into existence. To 

 take a simple example, if one parent has blue eyes and light 

 complexion, the other dark eyes and dark complexion, then 

 among their descendants vi^ill be some like the fair parent, 

 some like the dark parent, some w^ith blue eyes and dark 

 complexion, some with dark eyes and light complexion. If 

 the parents differ in many characteristics instead of but two, 

 the number of different combinations of characteristics 

 among their descendants is very great. 



In this production of new combinations through reproduc- 

 tion from two parents, there are three types of consequences 

 that are of interest for evolution. 



First, in this way there are produced combinations of genes, 

 and therefore combinations of characteristics, that have never 

 before existed. 



Second, in this way single qualities, powers or dimensions, 

 may be increased beyond the degree in which they have 

 before existed. 



Third, as a result of the recombinations of genes, character- 

 istics may appear in the descendants that have never occurred 

 in their ancestors, or in any other organism. 



In these three ways therefore, evolutionary change is 

 brought about by reproduction from two parents. We will 

 consider each of the three types of change separately. 



I. By biparental reproduction, any quality or peculiarity of 

 any individual or any stock may become combined with any 

 features of any other individual or stock with which it can 

 unite for parenthood. Thus are produced combinations of 

 characteristics that have never before been brought together. 

 This plays a great role in relation to the fitness or adaptiveness 



