14 THE MAMMALIA. 



with it. Whoever believes in the unity of the 

 human race must be a decided advocate of this 

 variability, even though it be but in the crude 

 notion of regarding the negroes as sun-burnt 

 white men, and the latter as bleached black men. 

 Those, however, who feel convinced of the contrary 

 maintain the variability to be the result of the un- 

 doubted mixing of the races and species. 



If we look upon the dog as having been created, 

 then the assumption of an extraordinary capacity 

 of adaptation is unavoidable, but it is equally so 

 to those who see in the domestic dog a number 

 of different species of tamed jackals. 



THE PHENOMENA OF CONVERGENCE. 



Even Goethe early recognised the fact that ex- 

 ternal influences ' the four elements ' to which 

 the animal has to submit and to adapt itself for 

 the necessity of self-preservation, change the form 

 and mode of life to so great an extent that re- 

 semblances have been produced between creatures 

 wholly different at first. But Goethe did not give 

 unequivocal expression to this thought till d'Alton 

 had very clearly emphasised the transformation 

 and development of organisms, as the result of 

 * elementary conditions.' A number of Goethe's 



