Coadaptation 33 



to weigh down the animal altogether. It is inconceivable, he says, 

 that so many processes of selection should take place simultaneously, 

 and we are therefore forced to fall back on the Lamarckian factor of 

 the use and disuse of functional parts. And how, he asks, could 

 natural selection follow two opposite directions of evolution in 

 different parts of the body at the same time, as for instance in the 

 case of the kangaroo, in which the forelegs must have become 

 shorter, while the hind legs and the tail were becoming longer and 

 stronger ? 



Spencer's main object was to substantiate the validity of the 

 Lamarckian principle, the cooperation of which with selection had 

 been doubted by many. And it does seem as though this principle, 

 if it operates in nature at all, offers a ready and simple explanation 

 of all such secondary variations. Not only muscles, but nerves, bones, 

 sinews, in short all tissues which function actively, increase in strength 

 in proportion as they are used, and conversely they decrease when 

 the claims on them diminish. All the parts, therefore, which depend 

 on the part that varied first, as for instance the enlarged antlers of the 

 Irish Elk, must have been increased or decreased in strength, in 

 exact proportion to the claims made upon them, just as is actually 

 the case. 



But beautiful as this explanation would be, I regard it as un- 

 tenable, because it assumes the transmissibility of functional modi- 

 fications (so-called "acquired" characters), and this is not only 

 undemonstrable, but is scarcely theoretically conceivable, for the 

 secondary variations which accompany or follow the first as corre- 

 lative variations, occur also in cases in which the animals concerned 

 are sterile and therefore cannot transmit anything to their de- 

 scendants. This is true of worker bees, and particularly of ants, and 

 I shall here give a brief survey of the present state of the problem as 

 it appears to me. 



Much has been written on both sides of this question since the 

 published controversy on the subject in the nineties between Herbert 

 Spencer and myself. I should like to return to the matter in detail, 

 if the space at my disposal permitted, because it seems to me that 

 the arguments I advanced at that time are equally cogent to-day, 

 notwithstanding all the objections that have since been urged against 

 them. Moreover, the matter is by no means one of subordinate 

 interest ; it is the very kernel of the whole question of the reality 

 and value of the principle of selection. For if selection alone does 

 not suffice to explain "harmonious adaptation" as I have called 

 Spencer's Coadaptation, and if we require to call in the aid of the 

 Lamarckian factor it would be questionable whether selection could 

 explain any adaptations whatever. In this particular case of worker 



D. 3 



