78 THE THEORY OF NATURAL SELECTION 



It is possible that variations of this nature may gradu- 

 ally lead to important and even to specific changes, 

 but whether this is the case still remains to be proved. 

 On the other hand, we shall see that specific differences 

 do sometimes arise at a single step, and there is strong 

 but indirect evidence to show that this is the way in 

 which a very great number of specific differences have 

 actually arisen. Indeed, some have contended that 

 this is the universal process by which such differences 

 originate, but this again is not proved, nor is it 

 altogether likely. In any case the inheritance of 

 acquired characters can have nothing to do with that 

 of definite and discontinuous differences. 



This is a problem to which we shall return in the 

 concluding chapter, in the light of further evidence con- 

 cerning continuous and discontinuous variations and 

 their manner of inheritance, which will be by that 

 time available. 



BIBLIOGRAPHY. 



DARWIN, CHARLES : The Origin of Species, sixth edition, 1872. 

 The Variation of Animals and Plants 



under Domestication, 1868. 

 ., The Descent of Man, 1871. 



,, The Various Contrivances by which 



Orchids are Fertilized by Insects. 

 ,, Different Forms of Flowers. 



The Movements and Habits of Climbing 



Plants. 



Insectivorous Plants. 



,, Life and Letters of Charles Darwin. 



,, ,, More Letters of Charles Darwin. 



MALTHUS, T. R. : An Essay on Population. 

 WALLACE, A. R. i Darwinism. 



