282 



HABIT AND INTELLIGENCE. 



[chap. 



Origin of 

 organic 

 forms by 

 the accu- 

 mulation 

 of varia- 

 tions. 

 Divergent 

 lines of 

 variation. 

 Diver- 

 gence and 

 re-diver- 

 gence. 

 Classifica- 

 tion is 

 genealogy. 



No re- 

 union 

 after 

 diver- 

 gence. 



Metamor- 

 phosis 

 generally 

 is pro- 

 gress. 



Exception 

 in Cirrhi- 

 pedes. 



Specific 

 change 

 also is 

 generally 

 progress. 



together. All organic forms have come into existence by 

 the accumulation of such variations, ever since they began 

 in those first vitalized but unorganized germs from which 

 I believe all organisms to be descended. Different forms 

 have come into existence by the accumulation of different 

 sets of variations along different and diverging lines of 

 descent ; and these lines ever diverge and re-diverge — that 

 is to say, forms ever become differentiated and re-differ- 

 entiated from each other — giving origin to subordinate 

 groups. Thus the true classification, could we find it, 

 would be a genealogical table ; and the best attainable 

 classification is that which most nearly approximates to 

 genealogical affinities. 



In the genealogical table of a human family, if it repre- 

 sents the whole of the family, and not the leading branch 

 only, there are such diverging and re-diverging lines of 

 descent. In the human genealogy, however, lines that 

 have diverged may reunite by the intermarriage of 

 cousins ; and thus a new line may arise, mixing the 

 blood, and probably combining the characters, of the two 

 parent lines. But in the organic genealogy such unions 

 are impossible ; for organisms cannot produce offspring 

 together after they have diverged into decidedly different 

 forms. In our organic genealogical tree, consequently, the 

 branches, which are classes, should never reunite after 

 diverging. 



Further, the facts of metamorphosis, as stated in the 

 last chapter, go to prove that when any important change 

 takes place it is generally towards a higher form. The 

 frog is higher than the tadpole, the butterfly is higher than 

 the caterpillar, and the crab is higher than the zoea ; and 

 though the cirrhipede is not higher than its nauplius-like 

 larva, this case is exceptional. And if it is true, as I have 

 shown reason for believing, that the ancestral forms from 

 which the species of these groups have been developed 

 resembled the larvse from which the individuals are still 

 developed, then the direction of change of species, as well 

 as of metamorphosis of the individual, is in general, 

 though not invariably, towards higher forms. 



