Evolution of Sex 351 



ceeded only by selection of parents both hornless. And other 

 examples will easily be found to show that heredities are 

 usually added in fusion. This is an important principle be- 

 cause it is the essence of progress in evolution. It is this 

 which makes successive generations higher in organization 

 and not merely fitter in low organization. It is by such addi- 

 tions that we see species rise in the scale of ability instead 

 of merely changing from one to another function. 



It is important to our study to note that when conjugation 

 occurs, any progress which has been achieved in heredity 

 on one side more than on the other, is not lost. It may be 

 diluted ; it may be continued in a certain number of the off- 

 spring, and if it is not continuously useful it may be over- 

 ruled, but if it is not too abnormal, it is preserved experi- 

 mentally. Conjugation then endows all the species which 

 practice it, with a distribution of the sum total of the heredi- 

 ties of all individuals. That is to say it works toward that 

 end, but the degree of achievement is of course limited and 

 various. Yet it is seen to be effective enough, when taken 

 together with the unifying effect of similarity of circum- 

 stances, to keep definite types dominant in certain locations. 

 Evidently there is in this process the influence against con- 

 fusion which we desired to find — all valuable variations and 

 differences tend to preserve themselves, not separately, but 

 by immediate distribution to, and amalgamation with, the 

 whole race, or at least with those parts which are in possible 

 contact. 



Let us again note in single-celled life the possibilities of 

 conjugation. Evidently union of two cells may produce 

 bulk greater than usual. So in due course when the union 



