Weismann s theory of Evolution (1891). 91 



it is not a fact. For, if the theory were sound, this 

 particular fact would certainly have admitted of de- 

 monstration : therefore the proof that it is not a fact 

 — but the reverse of a fact — amounts at the same time 

 to a disproof of the theory \ 



The only other line of evidence to be adduced in 

 favour of the absolute stability of germ-plasm is that 

 which is furnished by the high antiquity of some specific 

 types, by the facts of atavism, and by the persistency 

 of vestigial organs. But this line of evidence is as 

 futile as the other. Nobody has ever questioned 

 that hereditary characters are persistently stable as 

 long as they are persistently maintained by natural 

 selection ; and this, according to Weismann himself, 

 must have been the case with all long -enduring 

 species : these, therefore, fail to furnish any evidence 

 of the inherent stability of germ-plasm, which is the 

 only point in question. 



Again, as regards the facts of atavism, nobody is 

 disputing these facts. What we are disputing is 

 whether the degree of inherent stability which they 

 unquestionably prove can be rationally regarded as 



1 In his Essays (vol. i. p. 282) Weismann says: — "If it could be shown 

 that a purely parthenogenetic species had become transformed into a 

 new one, such an observation would prove the existence of some new 

 force of transformation other than selective processes, for the new species 

 could not have been produced by these latter." But now it has been 

 shown that a purely parthenogenetic species can be transformed into 

 a new one, and therefore it seems desirable to note that the observation 

 does not so much as tend to prove the existence of some new force 

 of transformation other than selective processes. For this most singular 

 statement can only stand on a prior acceptance of Weismann's own 

 assumption, as to amphigony being the only possible cause of individual 

 hereditary variation. Only if we have already, and with absolute 

 certainty, embraced the whole Weismannian creed, could we consent to 

 affirm that " natural selection is an impossibility in a species propagated 

 by a-sexual reproduction." 



