EVOLUTION AND HUMAN DESTINY 



jugation, but can also survive by means of binary- 

 fission alone. Such a reader may also be thinking of the 

 famous chicken heart tissue that was able to survive 

 in a proper nutrient solution for a long time. However 

 these objections do not invalidate the theory of even- 

 tual cell death by somatic mutations. It has been 

 accounted for, that simple cells, as a species, can survive 

 by fission alone. It is therefore not surprising that 

 there should be cells of an intermediate complexity 

 which can still get along by division only, but do at 

 the same time already exhibit the mechanism of con- 

 jugation. It is through such intermediate forms that 

 the most complex unicellular organisms must have 

 developed. Most varieties of paramecium, for example, 

 can no longer survive as species by fission alone. They 

 are already sufficiently complex, for conjugation to 

 have become a necessity, if the species is to continue. 



The chicken heart tissue probably consists of cells 

 which are relatively resistant to mutant damage. There- 

 fore these cells can exist for many generations without 

 showing a sufficient amount of damage to impair func- 

 tion. Also, as happens generally in the tissues of multi- 

 cellular organisms, the seriously mutated cells fail to 

 divide vigorously and die, while the undamaged ones 

 become the parents of new generations of healthy off- 

 spring. If such were not the case, the life of the more 

 complex multicellular organisms would be brief in- 

 deed. More than that, the potential life span of certain 



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