6 CHAPTERS ON EVOLUTION. 



Preservation of Favoured Races in the Struggle for Life ; " and such 

 a designation indicates with sufficient clearness that it was to "natural 

 selection " that Mr. Darwin attributed the chief power in evolving 

 new species through the modification of the old. Mr. Wallace 

 accepts " natural selection " as a true factor, but he does not regard it 

 as operating to the same extent in evolution as did Mr. Darwin. 

 Other biologists, again, are inclined to adopt the idea that the evo- 

 lution of living beings follows particular lines, along which the 

 process is guided or directed partly by internal causes inherent in 

 the constitution of the living being, and partly by external causes 

 and by the surroundings of life. Concerning the relative importance 

 of the various factors which biologists regard as of importance in 

 determining the process of evolution, Huxley remarks that the exact 

 place and power of " natural selection " " remains to be seen. Few 

 can doubt that, if not the whole cause, it is a very important factor 

 in that operation, and that it must play a great part in the sorting 

 out of varieties into those which are transitory and those which are 

 permanent. But," continues this high authority, " the causes and 

 conditions of variation have yet to be thoroughly explored, and the 

 importance of natural selection will not be impaired, even if 

 further inquiries should prove that variability is definite, and is 

 determined in certain directions rather than in others by conditions 

 inherent in that which varies. It is quite conceivable that every 

 species tends to produce varieties of a limited number and kind, 

 and that one effect of natural selection is to favour the development 

 of some of these, while it opposes the development of others along 

 their predetermined lines of modification." 



It forms no part of the purpose of this volume to discuss the 

 merits of these varied views respecting the exact nature of the 

 factors to which evolution owes its force and power. Perhaps any 

 exhaustive account of this aspect of the subject is at present im- 

 possible with the materials at command. That which is infinitely 

 more important in the first instance is the appreciation, firstly, of 

 what evolution at large is and implies ; and, secondly, of the proofs 

 and arguments on which the existence and operation of this process 

 may legitimately be based. A brief statement of the Darwinian 

 theory of evolution may, however, be given, inasmuch as this aspect 

 of the theory is that most frequently discussed and criticised both 

 in scientific and in popular circles. It should be clearly borne in 

 mind that the broad idea of evolution forms a foundation for every 

 theory of the special fashion in which that process may be conceived 

 to operate. " Darwinism " in this light is therefore to be regarded 

 merely as one, but also as probably the strongest phase of those 

 speculative endeavours to show the " how " of living nature, just as- 

 evolution itself has supplied the answer to most of the biological 

 " whys." 



