Sex as an Adaptation 441 



What we really need to know is whether or not the sexual 

 method was once acquired, because it was an advantage 

 to a particular organism, or to the species to reproduce in 

 this way. It is assumed by many writers that this was the 

 case, but whether they have sufficient ground for forming 

 such an opinion is our chief concern here. On the other 

 hand, it is conceivable, at least, that if the sexual method 

 once became established, it might continue without respect to 

 any superiority it gave over other methods, and might finally 

 become a necessary condition for the propagation of particu- 

 lar species. Thus the method would become essential to 

 propagation without respect to whether the species lost more 

 than it gained. Whichever way the balance should turn, it 

 might make little difference, so long as the species was still 

 able to propagate itself. 



Brooks made the interesting and ingenious suggestion that 

 the separation of the sexes has been brought about as a sort 

 of specialization of the individuals in two directions. The 

 male cells are supposed to accumulate the newly acquired 

 characters, and represent, therefore, the progressive element 

 in evolution. The female cells are the conservative element, 

 holding on to what has been gained in the past. It does not 

 seem probable, in the light of more recent work, that this 

 is the function of the two sexes, and it is unlikely that we 

 could account for the origin of the two sexes through the 

 supposed advantage that such a specialization might bring 

 about. A number of writers, Galton, Van Beneden, Biitschli, 

 Maupas, and others, have looked at the process of sexual re- 

 production as a sort of renewal of youth, or rejuvenescence 

 of the individuals. There is certainly a good deal in the 

 process to suggest that something of this sort takes place, 

 although we must be on our guard against assuming that 

 the rejuvenescence is anything more than the fulfilment of a 

 necessary stage in the life history. Weismann has ridiculed 

 this suggestion on the ground that it is inconceivable that 



