24 INTRODUCTION TO EVOLUTION 



in the limbs of terrestrial mammals (Fig. 3.3). The segments are short- 

 ened but they are all there in the order listed above. 



Thus we see that among birds and mammals limbs adapted for grasp- 

 ing, flying, running, and swimming are all constructed upon the same basic 

 pattern. They share a fundamental similarity of structure which is evi- 

 dently entirely unconnected with the uses to which they are put. How can 

 we explain the origin of similarity of this kind, similarity which has no 

 relation to function — which, indeed, exists in many cases despite dis- 

 similar functions? 



One way in which we might answer this question is that of the biologist 

 who first called attention to the fact that a basic pattern underlies all these 

 forelimbs. That was Cuvier, the eminent French comparative anatomist of 



FIG. 3.3. Skeleton of a whalebone whole. The upper figure shows rudi- 

 ments of the pelvic girdle and hindlimb; p, pubis; isch., ischium; f, femur. 

 (After Romanes; from Guyer, Animal Biology, Harper & Brothers, 1948, 

 p. 123.) 



the past century. Cuvier was not convinced of the truth of evolution. He 

 believed that each species of animal had been created separately, the idea 

 usually referred to as the theory of special creation. But if species were 

 separately created how could similarities between them arise? Obviously 

 they would be similar if they were created to resemble one another. More 

 specifically, we might assume that in shaping forelimbs the Creator used a 

 certain pattern; when he created the hand of man he modified that pattern 

 in a certain way; when he created the wing of a bat he modified the pat- 

 tern in a different way; when he created legs adapted for rapid running he 

 modified the pattern in still a different way; and so on. According to this 

 theory there is no genetic relationship between man, bat, and horse; all 

 they have in common is that they were made by the same Creator. In 

 much the same way a dressmaker may use a pattern in constructing a 

 dress of silk and then, changing it somewhat if necessary, to construct a 



