In his Origin of species, in the chapter entitled 'Mutual Affinities of Organic Beings: Morphology: Embryology: Rudimentary Organs', Darwin speaking of the nature of classification systems of living organisms, writes:

Such expressions as that famous one of Linnaeus, and which we often meet with in a more or less concealed form, that the characters do not make the genus, but that the genus gives the characters, seem to imply that something more is included in our classification, than mere resemblance. I believe that something more is included; and that propinquity of descent, the only known cause of the similarity of organic beings, is the bond, hidden as it is by various degrees of modification, which is partially revealed to us by our classifications.

What does he mean by "that the characters do not make the genus, but that the genus gives the characters"?