PRINCIPLE OF DIVERGENCE. 15 



In the Autobiography (Vol. I. p. 84) my father has stated 

 what seemed to him the chief flaw of the 1844 Sketch; he 

 had overlooked "one problem of great importance," the 

 problem of the divergence of character. This point is dis- 

 cussed in the ' Origin of Species,' but, as it may not be familiar 

 to all readers, I will give a short account of the difficulty and 

 its solution. The author begins by stating that varieties 

 differ from each other less than species, and then goes on : 

 " Nevertheless, according to my view, varieties are species in 

 process of formation How then does the lesser dif- 

 ference between varieties become augmented into the greater 

 difference between species ? " * He shows how an analogous 

 divergence takes place under domestication where an originally 

 uniform stock of horses has been split up into race-horses, 

 dray-horses, &c., and then goes on to explain how the same 

 principle applies to natural species. "From the simple 

 circumstance that the more diversified the descendants from 

 any one species become in structure, constitution, and habits, 

 by so much will they be better enabled to seize on many and 

 widely diversified places in the polity of nature, and so be 

 enabled to increase in numbers." 



The principle is exemplified by the fact that if on one plot 

 of ground a single variety of wheat be sown, and on to 

 another a mixture of varieties, in the latter case the produce 

 is greater. More individuals have been able to exist because 

 they were not all of the same variety. An organism becomes 

 more perfect and more fitted to survive when by division 

 of labour the different functions of life are performed by 

 different organs. In the same way a species becomes more 

 efficient and more able to survive when different sections of 

 the species become differentiated so as to fill different stations. 



In reading the Sketch of 1844, I have found it difficult to 

 recognise, as a flaw in the Essay, the absence of any definite 

 statement of the principle of divergence. Descent with 

 * 'Origin,' ist edit. p. in. 



