FIFTY YEARS' FJi OGRESS IN SCIENCE. 445 



inated missal, written in an unknown tongue; the graceful forms of the letters, 

 the beauty of the coloring, excited our wonder and admiration ; but of the true 

 meaning Httle was known to us; indeed we scarcely realized that there was any 

 meaning to decipher. Now glimpses of the truth are gradually rievealing them- 

 selves ; we perceive that there is a reason — and in many cases we know what 

 that reason is — for every difference in form, in size and in color; for every bone 

 and every feather, almost for every hair. Moreover, each problem which is 

 solved opens out vistas, as it were, of others perhaps even more interesting. 

 With this great change the name of our illustrious countryman, Darwin, is inti- 

 mately associated, and the year 1859 will always be memorable in science as 

 having produced his great work on "The Origin of Species." In the previous 

 year he and Wallace had published short papers, in which they clearly state the 

 theory of natural selection, at which they had simultaneously and independently 

 arrived. We cannot wonder that Darwin's views should have at first excited 

 great opposition. Nevertheless from the first they met with powerful support, 

 especially, in this country, from Hooker, Huxley and Herbert Spencer. The 

 theory is based on four axioms : — 



" I. That no two animals or plants in nature are identical in all respects. 



" 2. That the offspring tend to inherit the peculiarities of their parents. 



" 3. That of those which come into existence, only a small number reach 

 maturity. 



"4. That those, which are, on the whole, best adapted to the circum- 

 stances in which they are placed, are most likely to leave descendants." 



Darwin commenced his work by discussing the causes and extent of varia- 

 bility in animals, and the origin of domestic varieties; he showed the impossibility 

 of distinguishing between varieties and pointed out the wide differences which 

 man has produced in some cases — as, for instance, in our domestic pigeons, all 

 unquestionably descended from a common stock. He dwelt on the struggle for 

 existence (which has since become a household word), and which, inevitably re- 

 sulting in the survival of the fittest, tends gradually to adapt any race of animals 

 to the conditions in which it occurs 



While thus, however, showing the great importance of natural selection, he 

 attributed to it no exclusive influence, but fully admitted that other causes — the 

 use and disuse of organs, sexual selection, etc. — had to be taken into considera- 

 tion. Passing on to the difficulties of his theory he accounted for the absence of 

 intermediate varieties between species, to a great extent, by the imperfection of 

 the geological record. Here, however, I must observe that, as I have elsewhere 

 remarked, those who rely on the absence of links between different species really 

 argue in a vicious circle, because wherever such links do exist they regard the 

 whole chain as a single species. The dog and jackal, for instance, are now re- 

 garded as two species but if a series of links were discovered between them they 

 would be united into one. Hence in this sense there never can be links between 

 any two species, because as soon as the links are discovered the species are united. 

 Every variable species consists, in fact, of a number of closely connected links. 



