434 KINSHIP AND ADAPTATION 



the different kinds of plants that have ever Hved, we might 

 have a classification of the vegetable kingdom which could 

 be represented diagrammatically by an enormous tree, made 

 up of innumerable segments which would correspond to 

 successive generations of species. The twigs of one branchlet 

 would stand for the species of a genus; the branchlets of a 

 minor branch for the genera of a family; while these minor 

 branches and those larger and larger would represent in turn 

 families, orders, classes, and, finally, the main branches of 

 the kingdom. 



Let us suppose, now, that our evolving tree of life as it 

 grew was gradually buried, all except the tips of the twigs 

 which thus formed a flat top growing just above the surface 

 of the ground. Such a buried tree may show in a rough way 

 the nature of the facts presented to the evolutionist for inter- 

 pretation. Before him on the earth are living species ar- 

 ranged in groups of groups accorcUng to their various degrees 

 of resemblance. Below ground he may find a few more or 

 less fragmentary remains of creatures which lived and died 

 in ages past. By their resemblances to forms still living he 

 is able to tell roughly to what branch they may belong, and 

 if the extinct forms have peculiarities intermediate between 

 the characteristic features of living groups this would indicate 

 to him a kinship between these groups which he might not 

 have suspected. For example, certain coal plants, as Ave 

 shall see, which resemble both ferns and gymnosperms led 

 botanists to recognize a much closer kinship between these 

 groups than the living forms had made apparent. 



But by far the greater part of the buried generations have 

 left no remains and may be reconstructed only conjecturally 

 by reasoning backward to the ancestral traits from the 

 peculiarities possessed in common by their supposed descend- 

 ants. Sometimes it has happened that striking confirma- 

 tion of such reasoning has been found. Thus, to take an 

 example from the animal kingdom, zoologists were led to 

 believe from certain anatomical resemblances between birds 

 and reptiles that these groups were closely akin and must 

 have descended from a type com1)ining the fundamental 

 characteristics of both; then the fossil remains of a creature 



