The differences between the species in one genus are often trivial as against 

 the resemblances between two genera. Species must be "related" in the same 

 sense as cousins are related. The only question is, How far back in the family 

 tree can we find "common ancestors"? Our classifications suggest that if we 

 go back far enough, we may find that ducks and geese are related; or that all 

 birds are related; or that all fishes are related — that is, descended from the 

 same ancestors. If we go back still farther, we may find that all backboned 

 animals are descended from the same ancestors. 



There is no reason in advance against assuming that each species has been 

 separately created, or has otherwise arisen independently of all others, as have 

 artificial objects. If that were true, however, we might reasonably expect to 

 find, among the million or more distinguishable forms, at least an occasional 

 species that stood out by itself. It would be like a special commemoration 

 stamp, or some freak "gadget", which differs in its design from all its con- 

 temporaries. However, we find no such unique cases among organic species. 

 Even when we classify the extinct forms, we find that they fit logically into 

 the same general branching arrangement of living forms. 



Measures of Resemblance If we compare various insects, for example, 

 we shall find that most of the functions are carried on by corresponding organs 

 in the different animals. Thus the locomotive organs in bees, butterflies, and 

 grasshoppers are the legs and wings; and in every case the relative position 



© British Museum. World copyright strictly reserved 



A LIVING ARGUMENT ABOUT FOSSILS 



In 1939, off the coast of Africa, a living, breathing, scrapping Coelocanth was brought 

 up from the depths in a fishing net. He did not live very long, but long enough to 

 indicate that certain fossils found in old rocks correspond closely to an armored 

 fish that did actually live, although considered as long extinct 



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