The Significance of Sexual Reproduction 247 



they are, the greater the power of adaptation, the greater 

 the chance of victory. 



And in this I see the significance of sexual reproduc- 

 tion. It mixes the potentialities that have developed in 

 the single individuals in the most complete mariner imag- 

 inable; it achieves, at one stroke, all possible combina- 

 tions. It cancels, as Johannsen expresses it, the previous 

 correlation's. Asexual propagation confers a certain 

 degree of variability, and this may be quite sufficient in 

 many cases, especially in the case of a low organization 

 or of quite special adaptation, as in many parasitic and 

 saprophytic organisms. Under such conditions the vari- 

 ability remains, in a certain sense limited, more or less 

 one-sided, because every individual is the result of the 

 varying, but, on the whole, one-sided environment in 

 which his progenitors existed. Only an exchange of qual- 

 ities can help to overcome this one-sidedness ; only this 

 can cause all the combinations to arise which are de- 

 manded by the varying environments. If we assume that 

 the bearers of the individual characters are, as a rule, in- 

 dependent of each other during their exchange, and also 

 that the latter is ruled by chance, two pairs of character- 

 istics would directly result in four, three in eight, four 

 in sixteen combinations. The sum total of the points of 

 difference of two parents must therefore give rise to such 

 an incredible number of possibilities that no struggle 

 for existence, no annual rejection of hundreds and thou- 

 sands of germs could demand a richer material. 



Hence sexual reproduction brings individual variabil- 

 ity to its highest point. It produces a material that cor- 

 responds to almost any environment. It is the principal 

 condition for the greatest efficiency of cooperation, be it 

 by a selection as free as possible of the line of develop- 



