-6'6-Z 



HABIT AND INTELLIGENCE. 



[chap. 



explained 

 by the 

 theory of 

 develop- 

 meat. 



The deve- 

 lopment 

 theory 

 does not 

 answer the 

 question 

 of the 

 cause of 

 develop- 

 ment. 



through the whole vertebrate group ; and that when a new 

 organ is needed — as, for instance, a wing instead of a leg — 

 the type is not radically altered, but modified iu such a 

 way as to leave the same anatomical elements still dis- 

 cernible. There are some who regard it as a sufficient 

 answer to the question of the origin of species, to say that 

 the Creator has laid down plans, or types, for the Verte- 

 brata, and for each of the other great groups, and then 

 modified the vertebrate type to suit the special modes of 

 life of the fish, the quadruped, and the bird ; and the other 

 types in the same way. Now, as a statement of fact, this 

 is perfectly true ; but it is only a generalized statement of 

 fact — it is no explanation. The development theory takes 

 up the question at this point, admits the law of types as 

 true, and shows why it is true ; namely, that homological 

 resemblances are due to community of descent. The deve- 

 lopment theory does for the multitudinous facts of mor- 

 phology, embryology, and classification, what Kepler's laws 

 did for the mass of facts previously known concerning the 

 planetary motions : it shows how they are to be referred 

 to simple and intelligible principles. But Kepler's laws 

 left unanswered the question of the agency by which the 

 planetary motions were determined ; and the development 

 theory, considered merely as such, leaves unanswered the 

 question by what agency the development of species has 

 been produced. Any theory that wiU explain this will do 

 for the development theory what the Newtonian theory 

 of gravitation has done for Kepler's laws. Darwin 

 believes that he has discovered such a theory. I regard 

 his theory as not- false, but totally insufficient; partly 

 because, as I have shown at some length in the last 

 chapter, I do not believe it will in any degree explain 

 the more complex facts of organization ; partly because, 

 while it throws very great light on the variation of forms, 

 it throws little or none on the origin and variation of 

 tissues. 



I have not yet considered the geological evidence on the 

 subject of the origin and succession of organic forms. I 



