THE TAXONOMIC TREE 229 



lower Protista) into plants and animals is represented by the first 

 branching of the tree, the division of each of these great king- 

 doms into phyla by the next branching, and the subdivision of 

 phyla into classes, orders, families, genera, species and individuals 

 by the further ramifications, as shown in the accompanying 

 diagram (Fig. 86), which represents a mere fragment of the whole 

 tree selected to show the systematic position of a single species of 

 animal, the common brown bear, Ursus arctos. 



This great truth affords one of the most striking pieces of 

 evidence in favour of the theory of organic evolution, for the 

 tree-like form assumed by a natural classification bears an 

 unmistakable resemblance to the tree-like development of 

 the whole organic world which evolutionists believe to have 

 taken place. The two results represent, indeed, but slightly 

 different aspects of the same truth ; the resemblance between 

 them is no mere coincidence, but the fact that we are able 

 to classify organisms in a tree-like manner indicates very clearly 

 that these organisms have been produced by tree-like evolution. 



The systematist is now able to replace the vague groping after 

 " natural affinities " by a much clearer conception of the aims of 

 taxonomy. What he has to strive after is the elucidation of the 

 actual pedigrees of existing organisms, the unravelling of what is 

 termed their phylogeny or ancestral history. This means neither 

 more nor less than the ultimate reconstruction of the whole vast 

 tree of life. Piece by piece this is gradually being done, and it is 

 the great German biologist, Ernst Haeckel, who has led the way 

 in this particular department of biological investigation. Some 

 of the main branches of the tree have already been reconstructed 

 in a satisfactory manner, but it is a work of immense difficulty 

 and practically unlimited extent, and at every step opinions 

 differ as to the value of conflicting evidence and the interpreta- 

 tion of obscure facts. The greater part of the tree is dead and 

 gone beyond recall, and such fragmentary information concerning 

 extinct forms as may be supplied by the discovery of fossils can 

 only be supplemented by indirect evidence derived from the study 

 of existing organisms. 



We must now inquire a little more fully into the relation 

 between the tree-like form assumed by a natural system of 

 classification, or the taxonomic tree, as we may term it, and the 

 phylogenetic tree, which represents the actual pedigrees of 

 organisms. In the former (Fig. 86) the main trunk of the tree, 



