36 ORGANIC EVOLUTION — PHYSICAL 



must perish and leave no offspring, yet some of his 

 descendants, because they have varied extremely favour- 

 ably, must, when there is a struggle for existence, other 

 things equal, survive in greater numbers, and cause the 

 ultimate elimination of the offspring of the second. 

 Now, of two individuals, one of which produces offspring 

 without collaboration with another individual, and the 

 other in collaboration with another and somewhat dis- 

 similar individual, the offspring of the latter must tend 

 to vary more than the offspring of the former, and 

 therefore in the struggle for existence to bring about 

 their ultimate extinction, whereby only tlie descendants 

 of the individual that reproduced sexually, and which 

 inherited this peculiarity, would be left to continue 

 the race. Wcismann's hypothesis therefore appears to 

 be reasonable, and it is moreover supported by other 

 considerations, for if w^c assume, as we must, that non- 

 living chemical compounds, under conditions we are 

 ignorant of, did in the beginning of life pass over the 

 border sjmce and become living beings, it is difficult 

 to imagine how they could possibly have inultijilied 

 sexually from the very first — how sexual union can 

 have been the rule in the beginning. It seems more 

 reasonable to suppose that these earliest forms multi- 

 jjlied asexually by fission, and that conjugation only 

 occurred later, the purpose of it being to produce a 

 greater amount of variability among the offspring. 

 Possibly conjugation had its origin in attempts at canni- 

 balism, which, among such excessively simple types as 

 the first must have been, perhaps resulted in coalescence 

 instead of assimilation. The extermination of those 

 that multij^lied asexually appears therefore to be the 

 cause of the almost universal prevalence of sexual re- 

 production among low as well as among high organisms. 

 If it be asked, Why, if sexual reproduction produces 

 variability, and variability is of such importance, do low 



