22 GENETIC VARIATIONS 



such interaction of gene products may go in producing new 

 characteristics, not before seen, no one can say. 



All these three methods of operation occur in man as well 

 as in other organisms. They occur in relation to mental and 

 temperamental qualities as well as to others. One parent may 

 be industrious and ambitious, but fail in life because he is 

 mentally dull and slow. The other may be quick and acute 

 mentally, but fail because he lacks industry and ambition. 

 Among their descendants would be some that combine the 

 industry and ambition of one of the parents with the acute- 

 ness and quickness of the other. Such descendants would be 

 superior. By fusing thus all the best qualities of numbers of 

 different ancestors, persons far beyond the usual level would 

 be produced. Again, as we have seen, existing powers and 

 capabilities may in this manner be increased in degree, 

 and even qualities produced that did not before exist. Such 

 methods of operation are doubtless the origin of the individ- 

 uals that are superior to most of humanity, the geniuses, the 

 Goethes and Leonardos. 



Thus this method of operation by the formation of new 

 combinations through the mating of two individuals is 

 powerful in producing variation. A very large proportion of 

 the variety found among organisms is due to it. If reproduc- 

 tion occurred only by the division of single individuals, as 

 may occur in plants and many lower animals, the world 

 of living things would be relatively simple; there would be 

 comparatively few living types. The variety among organ- 

 isms is multiplied a thousandfold — perhaps a millionfold — 

 by reproduction from two parents instead of from one. 



And reproduction from two parents has, as we have seen, 

 great potentialities for the production of new types, and so 

 for bringing about progressive evolution. It is certainly one 

 of the greatest factors in evolutionary progress. 



