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segregation there would have been one case of isolation, but 

 after the segregation there would be five such cases. 



Vakiability. — The most important and fundamental cause 

 of evolution must necessarily be the innate tendency of all 

 organisms to vary one from the other, for a close inspection 

 reveals the fact that no two are exactly alike. It is found 

 again that in different species the range of individual varia- 

 bility varies to a considerable extent; that is, that some 

 species are more stable than others. So that conditions that 

 would cause some collections of individuals to evolve in cer- 

 tain directions may be quite inoperative when applied to 

 others. Romanes quotes as an example of the latter, the 

 goose, which Darwin calls an "inflexible type" as compared 

 with most other domesticated birds. He also refers to some 

 extremely striking examples quoted by Weissmann for the 

 sake of showing that there are cases which seem to tell 

 against the general principle of modification as due to 

 apogamy alone. These examples are four species of butter- 

 flies, belonging to three genera, which are identical in the 

 polar regions and in the Alps, notwithstanding that these 

 insects have been presumably separated from the parent 

 stocks since the glacial period ; and another example refers 

 to a fresh water crustacean (apus), the represenatives of 

 which are habitually compelled to form small isolated colo- 

 nies in widely separated ponds, and, nevertheless, exhibit no 

 divergence of character, although isolation has probably 

 lasted for centuries. Again, on Mount Kosciusko were 

 found specimens of flora and fauna characteristic of the 

 alpine regions of Tasmania. On the other hand, the land 

 mollusca of Maderia and the Sandwich Islands present diversi- 

 ties of types as numerous almost as the different sites suit- 

 able for local isolation. It is evident, therefore, that the 

 existence of this tendency or otherwise to individual varia- 

 bility must play a most important determining influence on 

 evolution. In the human species, where the type is pure, 

 the tendency to variability appears to be small, as may be 

 conveniently seen in the Jewish, Negro, ana Fellaheen types. 

 In the case of the Australian aboriginal, whether he is 

 autochthonous or an emigrant, he must have been isolated 

 for a lengthened period from other races of man due to his 

 geographical position. His type is found nowhere else, and 

 he has shown but little tendency to vary that type, so that 

 the presumption is on the side of an autochthonous origin. 

 The absence of a tendency to variability must, therefore, have 

 been an important factor in producing uniformity of type 

 amongst the Australian aborigines. 



