vi DIFFICULTIES AOT OBJECTIONS 149 



soil, climate, and atmosphere widely different from th'i se : : 

 their native habitat. Thus, many alpine plants only found 

 near perpetual snow thrive well in our gardens at the level of 

 the sea : as do the tritonias from the sultry plains of South 

 Africa., the yuccas from the arid hills of Texas and Mexico, and 

 the fuchsias from the damp and dreary shores of the Straits of 

 Magellan. It has been well said that plants do not live 

 where they like, but where they can ; and the same remark will 



to the animal world. Horses and cattle run wild and 

 thrive both in North and South America ; rabbits, once con- 

 fined to the south of Europe, have established themseL 

 our own country and in Australia : while the domestic fowl, a 

 native of tropical India, thrives well in every part of the 

 temperate zona 



If, then, we admit that when one portion of a species is 

 sepirated from the rest, there will necessarily be a slight 

 difference in the average characters of the two portions, it 

 does not follow that this difference has much if any effect 

 upon the characteristics that are developed by a long period 

 : isolation, In the first place, the difference itself will 



-.rily be very slight unless there is an exceptional 

 amount of variability in the 5] - and in the next place, 

 if the average characters of the species are the expression of 



Act adaptation to its whole environment^ then, given 

 a precisely similar environment, and the isolated portion will 

 inevitably be brought back to the same average of characters. 

 But, as a matter of fact, it is impossible that the environment 

 of the isolated portion can be exactly like that of the bulk of 

 the species. It cannot be so physically, since no two separated 

 areas can be absolutely alike in climate and soil ; and even if 

 the same, the geographical features, size, contour, and 

 relation to winds, seas, and rivers, would certainly differ. 

 Biologically, the differences are sure to be considerable. The 

 isolated portion of a species will almost always be in a much 

 smaller area than that occupied by the species is a whole, hence 

 it is at once in a different position as regards its own kind. 

 The proportions of all the other species of animals and plants 

 are also sure to differ in the two areas, and some species will 

 almost always be absent in the smaller which are present in 

 the larger country. These differences will act and react on 



