18 THE GENESIS OF SPECIES. [CHAP. 



Thus, every variation of a kind tending to save the life 

 of the individual possessing it, or to enable it more surely 

 to propagate its kind, will in the long-run be preserved, 

 and will transmit its favorable peculiarity to some of its 

 offspring, which peculiarity will thus become intensified till 

 it reaches the maximum degree of utility. On the other 

 hand, individuals presenting unfavorable peculiarities will 

 be ruthlessly destroyed. The action of this law of " Natural 

 Selection " may thus be well represented by the convenient 

 expression, " survival of the fittest." 8 



Now, this conception of Mr. Darwin's is, perhaps, the' 

 most interesting theory, in relation to natural science, 

 which has been promulgated during the present century. 

 Remarkable, indeed, is the way in which it groups together 

 such a vast and varied series of biological 4 facts, and even 

 paradoxes, which it appears more or less clearly to explain, 

 as the following instances will show. By this theory of 

 "Natural Selection," light is thrown on the more singular 

 facts relating to the geographical distribution of animals 

 and plants ; for example, on the resemblance between the 

 past and present inhabitants of different parts of the earth's 

 surface. Thus in Australia remains have been found of 

 creatures closely allied to kangaroos and other kinds of 

 pouched beasts, which in the present day exist nowhere but 

 in the Australian region. Similarly in South America, and 

 nowhere else, are found sloths, and armadillos, and in that 

 same part of the world have been discovered bones of ani- 

 mals different indeed from existing sloths and armadillos, 

 but yet much more nearly related to them than to any other 

 kinds whatever. Such coincidences between the existing 

 and antecedent geographical distribution of forms are nu- 



3 " Natural Selection " is happily so termed by Mr. Herbert Spencer 

 in his " Principles of Biology." 



4 Biology is the science of life. It contains zoology, or the science 

 of animals, and botany, or that of plants. 



