198 EVOLUTION [Chat-. Ill 



Letter 135 subjects have rather gone out of my head owing to orchids, 

 but I shall soon have to enter on them in earnest when I 

 come again to my volume on variation under domestication. 

 ... In the lifetime of an animal you would, I think, 

 find it very difficult to show effects of external condition on 

 'animals more than shade and light, good and bad soil, 

 produce on a plant. 



You speak of "an inherent tendency to vary wholly indepen- 

 dent of physical conditions " ! This is a very simple way of 

 putting the case (as Dr. Prosper Lucas 1 also puts it); but two 

 great classes of facts make me think that all variability is due 

 to change in the conditions of life : firstly, that there is more 

 variability and more monstrosities (and these graduate into 

 each other) under unnatural domestic conditions than under 

 nature ; and, secondly, that changed conditions affect in an 

 especial manner the reproductive organs— those organs which 

 are to produce a new being. But why one seedling out of 

 thousands presents some new character transcends the wildest 

 powers of conjecture. It was in this sense that I spoke of 

 " climate," etc., possibly producing without selection a hooked 

 seed, or any not great variation. 2 



I have for years and years been fighting with myself not 

 to attribute too much to Natural Selection — to attribute 

 something to direct action of conditions ; and perhaps I have 

 too much conquered my tendency to lay hardly any stress 

 on conditions of life. 



I am not shaken about "saltus,"* I did not write without 

 going pretty carefully into all the cases of normal structure 

 in animals resembling monstrosities which appear per saltus. 



1 Prosper Lucas, the author of Traite philosophique et physiologique 

 de Vhertditi naturelle dans les c'tats de sante et de maladic du systems 

 nerveux: 2 vols., Paris, 1S47-50. 



2 This statement probably occurs in a letter, and not in Darwin's 

 published works. 



3 Sir Joseph had written, March 1 7th, 1 862 : " Huxley is rather disposed 

 to think you have overlooked saltus, but I am not sure that he is right— 

 saltus quoad individuals is not saltus quoad species— as I pointed out in 

 the Begonia case, though perhaps that was rather special pleading in the 

 present state of science." For the Begonia case, see Life and Letters, 

 II., p. 275, also letter no, p. 166. 



