Classification. 31 
engaged in tracing when they proceeded ever more 
and more accurately to define these ramifications of 
natural affinity. But now, as just remarked,’we can 
clearly perceive that this underlying principle was none 
other than Heredity as expressed in family likeness, 
—likeness, therefore, growing progressively more 
unlike with remoteness of ancestral relationship. For 
thus only can we obtain any explanation of the sundry 
puzzles and apparent paradoxes, which a working out 
of their natural classifications revealed to botanists and 
zoologists during the first half of the present century. 
It will now be my endeavour to show how these 
puzzles and paradoxes are all explained by the theory 
that natural affinities are merely the expression of 
genetic affinities. 
First of all, and from the most general point of 
view, it is obvious that the tree-like system of classifi- 
cation, which Darwin found already and empirically 
worked out by the labours of his predecessors is as 
suggestive as anything could well be of the fact of 
genetic relationship. or this is the form that every 
tabulation of family pedigree must assume ; and there- 
fore the mere fact that a scientific tabulation of natural 
affinities was eventually found to take the form of a 
tree, is in itself highly suggestive of the inference that 
such a tabulation represents a famzly tree. If all 
species were separately created, there can be no assign- 
able reason why the ideas of earlier naturalists touch- 
ing the form which a natural classification would 
eventually assume should not have represented the 
truth—why, for example, it should not have assumed 
the form of a ladder (as was anticipated in the 
seventeenth century), or of a map (as was anticipated in 
