168 The Bible of Nature 



in illustration of this thesis is still unsatisfactorily 

 small, though it is interesting to note that each 

 valley in the Sandwich Islands seems to have its 

 own particular species of snail, just as almost 

 every mammal has its own peculiar parasites. 



An interesting corollary to the theory of isola- 

 tion has been pointed out by Professor Cossar 

 Ewart. Breeding within a narrow range often 

 occurs in nature as the result of geographical or 

 other barriers. In artificial conditions, this in- 

 breeding often results in the development of what 

 is called prepotency. This means that certain 

 forms have an unusual power of transmitting their 

 peculiarities, even when mated with dissimilar 

 forms. In other words, certain variations have a 

 strong power of hereditary persistence. There- 

 fore, wherever through inbreeding (which im- 

 plies isolation) prepotency has developed, there is 

 no difficulty in understanding that even a small 

 idiosyncrasy may come to stay. Reibmayr has 

 developed the interesting thesis that in the evolu- 

 tion of a successful human stock there must be an 

 alternation of long periods of inbreeding, in which 

 characters are fixed and prepotency developed, and 

 periods of outbreeding, in which fresh blood is intro- 

 duced and the possibility of new departures secured. 



General Retrospect. — Nature, Goethe said, is a 

 book whose every page is full of import, and that 

 is particularly true of the pages of the history of the 



