240 Animal Life and Intelligence. 



definite and perhaps considerable leaps under the influence 

 of changed conditions. We must not run the adage, Natura 

 nil facit per saltum, too hard, nor interpret saltum in too 

 narrow a sense. 



It is true, and we may repeat the statement of the fact 

 for the sake of emphasis, that we do not know how or why 

 this or that particular variation should result from this or 

 that change of climate, environment, or food-stuff ; nor do 

 we know why certain variations (such as that which pro- 

 duced the ancon breed of sheep) should be stable, while 

 other variations are peculiarly unstable. But in this we 

 are not worse off than we are in the study of inorganic 

 nature. We do not know why calcite should crystallize in 

 any particular one of its numerous varieties of crystalline 

 form ; we do not know why some of these are more stable 

 than others. We may be able to point to some of the 

 conditions, but we cannot be said to understand why 

 arragonite should be produced under some circumstances, 

 calcite under others ; or why the same constituents should 

 assume the form of augite in some rocks, and hornblende 

 in other rocks. We are hedged in by ignorance ; and 

 perhaps one of our chief dangers, becoming with some 

 people a besetting sin, is that of pretending to know more 

 than we are at present in a position to know. Our very 

 analogies by which we endeavour to make clear our mean- 

 ing may often seem to imply an unwarrantable assumption 

 of knowledge. 



In the last chapter I used the term " organic combina- 

 tion," and drew a chemical analogy. I wished to indicate 

 the particularity and the stability of certain variations, and 

 the possibility of new departures through new combinations 

 of variations, the new departure not being necessarily any- 

 thing like a mean between the combining variations.* I 

 trust that this will not be misunderstood as a new chemieo- 

 physical theory of organic forms. I have some fear lest I 

 should be represented as maintaining that a giraffe or a 

 peacock is a definite organic compound, with , its proper 



* See Darwin, "Animals and Plants under Domestication," vol. ii. p. 252. 



