566 THE HISTORY OF BIOLOGY 



the chromosomes, which unite in themselves all hereditary qualities. With 

 these we have at last arrived at something that can be observed; in fact, the 

 foregoing has been pure imagination, of the kind that the biologists of 

 the past century had such difficulty in avoiding when they had to explain 

 the phenomena of life. Darwin and Haeckel were content each with one 

 hypothetical unit of life; it can hardly be said that Weismann would have 

 done any special service to biology by burdening it with three of them. 



Theory of germinal selection 

 However, the germinal-plasm theory and its conclusions, both the ingen- 

 ious and the false, only served Weismann as a means for proving the doc- 

 trine that gradually came to mean for him the very corner-stone of biology: 

 the doctrine of the omnipotence of natural selection. The championship of 

 this theory, and the fight against that of the inheritance of acquired char- 

 acters eventually became his chief aim in life; all that could serve his pur- 

 pose he took to be good, while all that militated against it was rejected. 

 He went through many a hard struggle on behalf of his favourite theory; 

 in the nineties he was especially attacked by Herbert Spencer, who main- 

 tained the doctrine of the transmission of acquired characters, chiefly for 

 social reasons; it was, in fact, the precondition of human progress. But from 

 many other quarters also there arose the cry of "the impotence of natural 

 selection," and this cry was again taken up after the turn of the century. 

 Weismann's defence was often somewhat laboured; against Spencer he de- 

 fended himself mostly on the old argument about the intelligence of the 

 workers among the bees, which cannot be transmitted by inheritance, since 

 they are sterile, and which therefore cannot be directly "acquired" either. 

 It was more difficult to answer the question as to how that finality arose 

 that shows itself in occasional encroachments upon an organism; how, for 

 instance, a fracture heals in certain definite ways; the fracture certainly can- 

 not be traced to natural selection. Here Weismann found support in a theory 

 that was produced by the afterwards famous experimental biologist Roux, 

 who in his youth published a work entitled Der Kampfder Teile im Organismus. 

 Here an attempt is made to explain what Roux calls ' ' functional adaptation 

 within the organism: that every organ, even every cell, possesses its given 

 structure, which changes if the conditions of the organ's function are changed, 

 so that in normal circumstances the life of the body runs its even course; 

 if this is disturbed by interference from outside, cells and tissues adapt them- 

 selves as required to repair the damage. This fact Roux considers to be due 

 to a "struggle for existence" between the cells in the body and even between 

 the molecules in every cell, each of which strives to force its way forward 

 at the expense of its neighbours, an effort that is controlled by the general 

 requirements of the body, the weakest elements being thrust aside and de- 

 stroyed. This theory, to which we shall revert in another connexion, at 



