GEORGE FORSTER. lOI 



more easily effected, and more often produce fertile off- 

 spring than the unquestionably rarer crosses of species 

 the frequent failure of crosses between species com- 

 ])]etely accords with the modification of species in the 

 lapse of time, as shown above. Provisionally, let us 

 hold nothing to be established but that, as to fertility 

 and the capability of persistent reproduction, the 

 conditions of mongrels and of hybrids are essentially 

 similar and differ only in degree, and that on these 

 properties, no closer definition or limitation can be 

 founded. 



If the older definitions of species go back to Paradise, 

 and derive existent species lineally from ancestral pro- 

 genitors, miraculously created from the first and never 

 modified, the ingenuous statements of Linnaeus show that 

 all this was accepted as self-evident, and that no thought 

 was given to the proof, which would indeed have been 

 impossible to obtain. A letter from George Forster to 

 Peter Camper, dated May 7th, 1787, proves howevei 

 that, even in the last century, the voices of more far- 

 sighted naturalists w^ere raised against this superficial 

 treatment of the idea of species. Systems, he said, were 

 founded on this idea, yet everything was uncertain as 

 long as this expression was not irremovably fixed. But 

 hitherto all definitions of this word were hypothetical, 

 and in themselves anything but clear. If we are to 

 accept as many species as were created, how is a 

 created species to be distinguished from one produced 

 by the intermixture of several others ? To fall back 

 upon the Creation is to lose oneself in the Infinite 

 and the Impalpable. *' This will never enable us to 

 understand anything ; and definitions which rest on an 



