4 PREFACE. 



variation exists, but not predestined variation, run- 

 ning on independently of the life-conditions of the 

 organism, as Naegeli, to mention the most extreme 

 advocate of this doctrine, has assumed ; on the con- 

 trary, the variation is such as is elicited and con- 

 trolled by those conditions themselves, though indi- 

 rectly. 



In basing my proof of the doctrine of Germinal Se- 

 lection on the fundamental conceptions of my theory of 

 heredity, a few words of justification are necessary, 

 owing to the fact that the last-mentioned theory has 

 been widely and severely assailed since its first emer- 

 gence into light and even repudiated as absolutely 

 futile and erroneous. 



In the first place, many critics have characterised it 

 as a "pure creation of the imagination." And to a 

 certain extent it is such, as every theory is. But is 

 it on that account necessarily wrong? Can not its 

 fundamental ideas still be quite correct, and it itself 

 therefore perfectly justified as a means of further 

 progress ? 



Surely my critics cannot be ignorant of the promi- 

 nent part which imagination has recently played in 

 the exactest of all natural sciences physics? Are 

 they unaware that the English physicist Maxwell 

 "constructed from liquid vortices and friction-pulleys 

 enclosed in cells with elastic walls, a wonderful mech- 

 anism, which served as a mechanical model for electro- 

 magnetism"? 1 He hoped "that further research in 

 the domain of theoretical electricity would be pro- 

 moted rather than hindered by such mechanical fic- 



1 See Boltzmann, Mcthoden dcr theor. Physik, Munich, 

 1892. (In the Catalogue of the Mathematical Exhibit.) 



