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 



