32 Evolution and Adaptation 



Evidence in Favor of the Transmutation Theory 

 evidence from classification and from comparative 



ANATOMY 



It does not require any special study to see that there are 

 certain groups of animals and of plants that are more like 

 each other than they are like the members of any other group. 

 It is obvious to every one that the group known as mammals 

 has a combination of characters not found in any other 

 group ; such, for instance, as a covering of hair, mammary 

 glands that furnish milk to the young, and a number of other 

 less distinctive features. These and other common character- 

 istics lead us to put the mammals into a single class. The 

 birds, again, have certain common characters such as feathers, 

 a beak without teeth, the development of a shell around the 

 egg, etc., and on account of these resemblances we put them 

 into another class. Everywhere in the animal and plant 

 kingdoms we find large groups of similar forms, such as the 

 butterflies, the beetles, the annelidan worms, the corals, the 

 snails, the starfishes, etc. 



Within each of these groups we find smaller groups, in 

 each of which there are again forms more like each other 

 than like those of other groups. We may call these smaller 

 groups families. Within the families we find smaller groups, 

 that are more like each other than like any other groups in 

 the same family, and these we put into genera. Within the 

 genus we find smaller groups following the same rule, and 

 these are the species. Here we seem to have reached a limit 

 in many cases, for we do not always find within the species 

 groups of individuals more like each other than like other 

 groups. Although we find certain differences between the 

 individuals of a species, yet the differences are often incon- 

 stant in the sense that amongst the descendants of any in- 

 dividual there may appear any one of the other variations. 

 If this were the whole truth, it would seem that we had here 



