ABSTRACT
This chapter expresses that the life of each species depends in a more important manner on the presence of other already defined organic forms, than on climate. The main cause, however, of innumerable intermediate links not now occurring everywhere throughout nature, depends on the very process of natural selection, through which new varieties continually take the places of and supplant their parent-forms. By the theory of natural selection all living species have been connected with the parent-species of each genus, by differences not greater than one sees between the natural and domestic varieties of the same species at the present day; and these parent-species. All geological facts tell that each area has undergone slow oscillations of level, and apparently these oscillations have affected wide spaces. All the grand leading facts of geographical distribution are explicable on the theory of migration, together with subsequent modification and the multiplication of new forms.
