180 THE ORIGIN OF SPECIES 



alluded to that in America the law of distribution of 

 terrestrial mammals was formerly different from what it 

 now is. North America formerly partook strongly of the 

 present character of the southern half of the continent; 

 and the southern half was formerly more closely allied 

 than it is at present to the northern half. In a similar 

 manner we know, from Falconer and Cautley's discover- 

 ies, that Northern India was formerly more closely re- 

 lated in its mammals to Africa than it is at the present 

 time. Analogous facts could be given in relation to the 

 distribution of marine animals. 



On the theory of descent with modification, the great 

 law of the long enduring, but not immutable, succession 

 of the same types within the same areas is at once ex- 

 plained; for the inhabitants of each quarter of the worldly 

 ■will obviously tend to leave in that quarter, during thelji 

 next succeeding period of time, closely allied though Ipj 

 in some degree modified descendants. If the inhabitants l|: 

 of one continent formerly differed greatly from those ofli;. 

 another continent, so will their modified descendants still Ei 

 differ in nearly the same manner and degree. But after Itj, 

 very long intervals of time, and after great geographical 

 changes, permitting much intermigration, the feebler will 

 yield to the more dominant forms, and there will be 

 nothing immutable in the distribution of organic beings. 



It may be asked in ridicule, whether I suppose that 

 the megatherium and other allied huge monsters, which 

 formerly lived in South America, have left behind them 

 the sloth, armadillo, and anteater, as their degenerate 

 descendants. This cannot for an instant be admitted. 

 These huge animals have become wholly extinct, anu_j^ 

 have left no progeny. But in the caves of Brazil the 



