DARWIN ON THE ORIGIN OF SPECIES 125 



not to be violated for the sake of practical convenience 

 or log^ical rules, but he was unable to explain what 

 he meant by it. Linnaeus tried to illustrate affinity 

 between plants by contiguous provinces on a map, a 

 better metaphor than the linear scale, for the scale can 

 only express affinity on two sides, while the map can 

 express affinity on many. His practical experience of 

 plassification taught him a truth, shocking at first 

 sight to the logician^ — viz., that the characters which 

 serve for the definition of one genus may be useless for 

 the definition of the next, and he laid it down that the 

 characters do not make the genus, but the genus the 

 characters. After Linnaeus we find for a long time no 

 advance in the philosophy of natural classification. 

 Cuvier (1816) is even retrograde, for he sets aside the 

 maxims of Linnaeus, maintains that adaptive characters 

 (characters closely related to the conditions of life) are 

 relatively constant, and that large groups should be 

 defined by characters drawn from organs of great 

 physiological importance. These decisions of his are 

 repudiated by later naturalists. 



The key to the affinity puzzle which had so long 

 baffled thinking naturalists was at last supplied by 

 Darwin, who explained that "the natural system is 

 founded on descent with modification ; that the char- 

 acters which naturalists consider as showing true 

 affinity between any two or more species, are those 

 which have been inherited from a common parent, all 

 true classification being genealogical ; that community 

 of descent is the hidden bond which naturalists have 



* Titius of Wittenberg-, who published in 1766 what is commonly 

 called Bode's law of planetary distances, objected to the Linnean 

 system on the ground that it multiplied the principle of division. 

 {De divisione animalium generali, 1760.) 



