ORDERLINESS AMONG ANIMALS 



107 



ther grouped the orders into six classes, his 

 largest category. Since his time, of course, 

 a great many biologists have unearthed 

 information about more and more animals 

 so that it became necessary to enlarge his 

 classification extensively. This was done by 

 adding two more groups, namely, families 

 (between genera and orders) and phyla 

 (the largest group of all). Furthermore, 

 each group has been subdivided again and 

 again, so that we now have the following 

 general categories: phylum, subphylum, 

 class, subclass, order, suborder, family, sub- 

 family, genus, subgenus, species, and sub- 

 species. However, not all of these divisions 

 are necessary in the classification of every 

 animal. 



The differences are less and less as the 

 selection moves from the phylum to the 

 species. For example, the differences be- 

 tween the horse and the earthworm are 

 various and striking; each belono;s to a 

 separate phylum. The differences between 

 the horse and the alligator, while many, are 



in different orders, families, genera, and 

 species. 



In many cases, however, the problem of 

 separating species is much more difficult. 

 In fact, a point is reached where biologists 

 are frequently in doubt as to whether or 

 not a given animal is actually a separate 

 species at all. This is as one would expect 

 if the theory of evolution holds, namely, 

 that animals have originated and are in- 

 deed still originating from a common an- 

 cestral stock. Undoubtedly new species are 

 forming at the present time and will con- 

 tinue to do so as long as there is life on 

 earth. This problem occupied the attention 

 of Charles Darwin, whose lifelong efforts 

 culminated in his book. The Origin of Spe- 

 cies, which conveys the answers to many 

 questions concerning species differences. 



The following table illustrates the use of 

 the Linnaean system in classifying man ac- 

 cording to his distinguishing characteristics 

 and in outlining the basis of his relationship 

 to other animals: 



Phylum Chordata — notochord, gill slits, nerve cord 

 Subphylum Vertebrata — backbone 



Class Mammalia — mammary glands, hair 

 Subclass Eutheria — placenta 



Order Primates — superior nervous system 



Suborder Anthropoidea — flattened or cupped nails 

 Family Hominidae — no tail or cheek pouches 

 Genus Homo — manlike 



Species sapiens — present-day man 



not nearly as numerous as those between 

 the horse and the earthworm; they belong 

 to the same phylum but not to the same 

 class. Thev show more differences than are 

 observed between the horse and the dog, 

 both mammals, belonging to the same class. 

 The differences between the dog and the 

 horse are sufficient, however, to place them 



Thus Homo sapiens includes all living 

 men today. To distinguish between differ- 

 ent colors and other characteristics of men, 

 the subspecies is given. The scientific name 

 then becomes trinomial, such as Homo 

 sapiens africanus, which identifies a par- 

 ticular race of living men, the African 

 Negro. 



