THE CONTINUITY OF CELLS 



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24 single chromosomes in the germ cells. 

 The possible chromosome combinations 

 then become 2 raised to the 24th power, or 

 16,777,216. If we multiply this figure by 8 

 we arrive at the number of kinds of serm 

 cells it is possible for one person to pro- 

 duce. Providing it were possible, one couple 

 could become the parents of all of the peo- 

 ple in the world and no two of their off- 

 spring need be exactly alike. 



Because of this wide variability among 

 germ cells, the offspring resulting from their 

 union are different from each other and 

 from either parent. They are new and dif- 

 ferent individuals, each with its own respec- 

 tive parts assembled in a slightly different 

 manner from any other members of the 

 species. This makes for great variability 

 among species, which is the fundamental 

 reason why evolution has gone on the way 

 it has. Without variation there would be 

 no way for animals to become better suited 

 to their environment because they would 



all be exactly alike, hence no one of them 

 would be able to explore a new situation 

 any better than another. This is what hap- 

 pens when asexual reproduction is the only 

 means of reproduction. While it is generally 

 confined to the lower animals, it is known 

 to occur among some plants under man's ■ 

 cultivation. The seedless orange trees, for 

 example, are all grown from grafts, so that 

 actually all that is done is to increase the 

 size of the original tree. Since all of the 

 cells carry the same genes, they have no 

 opportunity for variation and must there- 

 fore all be exactly alike, barring an occa- 

 sional mutation. Most of the lower inverte- 

 brate animals reproduce asexually as well 

 as sexually. In the former case they likewise 

 have no opportunity for variation. Sexual 

 reproduction evolved very early among ani- 

 mals and is probably largely responsible for 

 subsequent evolution of more complex 

 forms. 



