Sex as an Adaptation 449 



energy ; amphimixis must rather be advantageous for the 

 maintenance and modification of species. As soon as we 

 admit that amphimixis confers some such benefits, it is clear 

 that the latter must be augmented, as the method appears 

 more frequently in the course of generations ; hence we are 

 led to inquire how nature can best have undertaken to give 

 this amphimixis the widest possible range in the organic 

 world." Nature, Weismann says, could find no more effec- 

 tual means of bringing about the union of the sexual cells 

 than by rendering them incapable of developing alone. 

 " The male germ-cells, being specially adapted for seeking 

 and entering the ovum, are, as a rule, so ill provided with nu- 

 triment that their unaided development into an individual 

 would be impossible ; but with the ovum it is otherwise, and 

 accordingly the 'reduction division' removes half the germ- 

 plasm and the power of developing is withdrawn." It can 

 scarcely be claimed, in the light of more recent discoveries, 

 that the reduction division takes place in order to prevent the 

 development of the ovum, for how then could we explain the 

 corresponding division of the male germ-cells ? 



Whatever means has been employed to bring about the pro- 

 cess of sexual reproduction, the guiding principle is supposed 

 by Weismann to be natural selection as stated in the following 

 paragraph : " If we regard amphimixis as an adaptation of 

 the highest importance, the phenomenon can be explained in a 

 simple way. I only assume that amphimixis is of advantage 

 in the phyletic development of life, and furthermore that it is 

 beneficial in maintaining the level of adaptation, which has 

 been once attained, in every single organism ; for this is as 

 dependent upon the continuous activity of natural selection as 

 the coming of new species. According to the frequency 

 with which amphimixis recurs in the life of a species, is the 

 efficiency with which the species is maintained ; since so 

 much the more easily will it adapt itself to new conditions of 

 life, and thus become modified." 



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