63 



considered nature to be always in a state of flux and move- 

 ment, and expressed the opinion that " nature could effect 

 anything with the forces at her disposal, except create 

 matter and destroy it." Dr. Erasmus Darwin and Lamarck 

 both held that changes in species were caused by the direct 

 action of their environment, and by the use or disuse of 

 their various organs. St. Hilaire, Herbert Spencer, and 

 others elaborated views of a similar character ; but it was 

 not until the publication of "The Origin of Species" that 

 a theory at all commensurate with the importance of the 

 subject, with the mass of facts already collected, and gener- 

 ally applicable to the various forms of organic life, was 

 elaborated to explain the process of organic evolution, nor had 

 any previous writer been able to show in what manner organic 

 beings responded to and were especially adapted to exist in 

 their environment, nor how known natural laws had been 

 able to produce the complex adaptations, as exhibited by the 

 various organs, to the environment in which each individual 

 lived. The explanation of the process of organic evolution 

 as enunciated by Darwin was, therefore, readily received by 

 scientific men, not as an actual explanation of all the facts 

 connected with the subject, but as a theory that helped to 

 explain many of the difficulties that had hitherto obscured 

 the manner of evolution, and the mode of operation of the 

 forces at work in its production, by an appeal to natural 

 laws ; and his theory of natural selection, although by no 

 means accepted in all its details at the present time, still 

 remains with some modifications as to detail, as facts 

 have since accumulated, the basis of the theory of the lines 

 on which evolution has taken place, and is generally considered 

 to be the main if not exclusive means of the modifications 

 that organic beings have undergone and are now under- 

 going. 



Variation is the fundamental factor of the Darwinian 

 theory of natural selection. It is quite safe to say that no 

 two organic beings are exactly identical in all their cha- 

 racters, and the amount of difference between individuals 

 of the same species, not only in size, shape, colour, and 

 external characters generally, but in the performance of 

 their vital functions, is much greater than has been generally 

 granted or is now generally believed ; and this variation 

 in the performance of the vital functions of an organism is 

 of the greatest importance, for, in some degree at least, 

 certain external variations are but the expression of this 

 internal variation, which may be rapidly weeded out by 



