20 GENETIC VARIATIONS 



of organisms. The result may be individuals superior in some 

 respects to any that have before existed, so that a distinct evo- 

 lutionary advance has been made. One stock may have 

 strength and agility, but also poor sight and hearing. Another 

 may have acute senses, but be weak and slow. By the mating 

 of the two, some offspring may be produced that have all the 

 superior qualities combined: strength, agility and acute 

 senses. Such combinations have a great advantage over either 

 of the parent stocks; a superior type has been produced. 

 Superior combinations are thus produced in thousands of 

 different ways, by the mating of diverse stocks. 



Of course inferior combinations are produced too in the 

 same manner. By mating the stock that is strong and agile 

 but has poor sight and hearing, with the one that is weak and 

 slow but has acute senses, some combinations are produced 

 with all the inferior qualities; they are weak, slow, and have 

 poor senses. Such individuals are not successful in the strug- 

 gle of life; they soon disappear, leaving only the better com- 

 binations. Along with the production of new combinations 

 by biparental reproduction, there is selective elimination on 

 a large scale, getting rid of the poor combinations, retaining 

 those that are efficient. Thus through the formation of new 

 combinations, along with selective elimination, progress is 

 brought about. 



2. The second effect of biparental reproduction is the 

 strengthening or increase of single powers and qualities, 

 beyond the previously existing degree. It is known that size, 

 strength, vigor, acuteness of senses, and other faculties or 

 characteristics that play an important role in life, do not 

 depend on single genes only; each is known to be influenced 

 by many diverse genes. Some of these genes are of superior 

 type in some individuals, others are superior in other individ- 

 uals. Thus one individual or race may carry a certain number 



