34 Evolution and Adaptation 
Having discovered that it is possible to arrange animals 
and plants in groups within groups, the question arises as to 
the meaning of this relation. Have these facts any other 
significance than that of a classification of geometric figures, 
or of crystals according to the relations of their axes, or of 
bodies as to whether they are solids, liquids, or gases, or even 
whether they are red, white, or blue? 
If we accept the transmutation view, we can offer an 
explanation of the grouping of living things. According to 
the transmutation theory, the grouping of living things is due 
to their common descent, and the greater or less extent to. 
which the different forms have diverged from each other. It 
is the belief in this principle that makes the classification of 
the biologist appear to be of a different order from that in 
any other science; and it is this principle that appears to give 
us an insight into a large number of phenomena. 
For example, if, as assumed in the theory, a group of 
individuals (species) breaks up into two groups, each of these 
may be supposed to inherit a large number of common char- 
acteristics from their ancestors. These characters are, of’ 
course, the resemblances, and from them we conclude that 
the species are related and, therefore, we put them into the 
same genus. The differences, as has been said, between the 
species must be explained in some other way; but the prin- 
ciple of classification with which we are here concerned is 
based simply on the resemblances, and takes no account of 
the differences between species. 
In this argument it has been tacitly assumed that the 
transformation of one species into another, or into more 
than one, takes place by adding one or more new characters 
to those already present, or by changing over a few char- 
acters without altering others. But when we come to examine 
any two species whatsoever, we find that they differ, not only 
in one or in a few characters, but in a large number of points; 
perhaps in every single character. It is true that sometimes 
