DIVERGENCE 265 



world, may be explained. It is a truly wonderful fact the 

 wonder of which we are apt to overlook from familiarity that 

 all animals and all plants throughout all time and space should be 

 related to each other in groups, subordinate to groups, in the 

 manner which we everywhere behold namely, varieties of the 

 same species most closely related, species of the same genus less 

 closely and unequally related, forming sections and sub-genera, 

 species of distinct genera much less closely related and genera 

 related in different degrees, forming sub-families, families, orders, 

 sub-classes and classes. The several subordinate groups in any 

 class cannot be ranked in a single file, but seem clustered round 

 points, and these round other points, and so on in almost endless 

 cycles. If species had been independently created, no explanation 

 would have been possible of this kind of classification; but it is 

 explained through inheritance and the complex action of natural 

 selection, entailing extinction and divergence of character as we 

 have seen." 



"The affinities of all the beings of the same class have some- 

 times been represented by a great tree. I believe this simile 

 largely speaks the truth. The green and budding twigs may 

 represent existing species, and those produced during former years 

 may represent the long succession of extinct species. At each 

 period of growth all the growing twigs have tried to branch out on 

 all sides, and to overtop and kill the surrounding twigs and 

 branches, in the same manner as species and groups of species 

 have at all times overmastered other species in the great battle for 

 life. The limbs, divided into great branches, and these into lesser 

 and lesser branches, were themselves once, when the tree was 

 young, budding twigs; and this connection of the former and 

 present buds by ramifying branches may^ well represent the 

 classification of all extinct and living species in groups subordinate 

 to groups. Of the many twigs whicn once flourished when the 

 tree was a mere bush, only two or three, now grown into great 

 branches, yet survive and bear the other branches; so with the 

 species which lived during long past geological periods, very few 

 have left living and modified descendants. From the first growth 

 of the tree many a limb and branch has decayed and dropped off; 

 and these fallen branches of various sizes may represent those 

 whole orders, families and genera which have now no living 

 representatives and which are known to us only in a fossil state. 

 As we here and there see a thin, straggling branch springing from 

 a fork low down in a tree, and which by some chance has been 

 favored and is still alive on its summit, so we occasionally see an 

 animal like the Ornithorhynchus or Lepidosiren, which in some 

 small degree connects by its affinities two large branches of life, 

 and which has apparently been saved from fatal competition by 

 having inhabited a protected station. As buds give rise by growth 

 to fresh buds, and these, if vigorous, branch out and overtop on 

 all sides many a feebler branch, so by generation I believe it has 

 been with the great Tree of Life, which fills with its dead and 

 broken branches the crust of the earth, and covers the surface 

 with its ever-branching and beautiful ramifications." 



