trated and compared, comparative morphology can be said 

 to have really begun. This early stage involved only the 

 crudest illustrations and superficial descriptions of the anat- 

 omy of various animals; yet even here could be found a hint 

 of the emerging concept of homology. The similarities in the 

 structure of man and the lower animals invited comparisons, 

 some of which were extremely improbable in terms of our 

 present understanding. The study of the anatomy of man, 

 reinstituted by Vesalius (1543), now became comparative 

 both in terms of structural variations and in terms of the 

 function of the various parts of the body. 



An important anatomical and physiological milepost was 

 Harvey's (1628) description and proof of the circulation of 

 the blood, based upon the structure and functioning of the 

 heart, and the direction of flow in the larger blood channels. 

 What was lacking was observation of the capillaries which 

 connect the arteries and veins. The significance of this work 

 lies in its mechanistic interpretation of what had been con- 

 sidered the seat of vitalism in man. The paradox is that in 

 other respects Harvey was quite loath to break with tradition. 

 The first compendium of "Comparative Anatomy," that 

 of Samuel Collins (1685), was based on the functional 

 approach. "The structure of one animal throws light on, and 

 explains, that of another, for comparative anatomy is the 

 most liberal and accurate guide. Parts which are dark and 

 incomprehensible in one animal may often be understood 

 very clearly in another." (Swammerdam, 1737) 



Daubenton (c. 1750) collaborated with Buffon in an ex- 

 tensive comparative study of mammals, and as a result Buf- 

 fon developed ideas of homology of structure. Homology 

 implies that a structure in one organism is the same or nearly 

 the same, however specialized in form or function, as that 

 in another organism. The problem is one of defining what is 

 meant by same. In the minds of these early biologists, 

 homology merely involved a fundamental plan of structure. 

 All vertebrates were assumed to be built on a common plan 

 with each species showing certain divergences from this plan 

 as specializations for its way of life. This idea of a fun- 

 damental plan was carried to the extreme of assuming 

 a basic one for all animals. 



Richard Owen (1843) was the first to define the terms 

 "homology" and "analogy," and discussion as to their 

 meaning has continued right down to the present time. 

 Whether a structure is truly homologous (the same) or anal- 

 ogous (similar only in function) depends now on our concept 

 of evolution. Homologous structures trace back to the same 

 part, more or less, of a common ancestor; analogous struc- 

 tures do not. 



Following Daubenton, many individuals (Goethe, Vicq 

 d'Azyr, Geoffroy Saint-Hilaire, and Cuvier) helped expand 

 our knowledge of vertebrate structure and systematized it so 

 as to realize the "greater truths" demanded of it by Buffon. 

 These "greater truths," in some instances, turned out to be 

 wild speculations. Many of these are fascinating, such as 

 Goethe's (or Oken's) theory that the skull is made up of 

 several modified vertebrae or the view held by many that 



nature is an organism which shows a single graded series of 

 forms from matter to man. The amateur status of some of 

 these philosophers as well as the general metaphysical at- 

 mosphere in which they lived accounts for some of these 

 hypotheses. 



In the hands of Cuvier (1829) anatomical facts were con- 

 servatively interpreted in terms of specializations for different 

 ways of life. He thought they represented several taxonomic 

 hierarchies rather than one "great chain of being," although 

 he did not believe in the mutability of species or evolution. 

 His interest in fossil forms gave the subject a new dimension, 

 one largely relegated to paleontology at the present time. 

 His work with fossils produced a catastrophe theory which 

 involved only local exterminations of life followed by inva- 

 sions of animals from other regions of the world. This view 

 could not stand up under close examination — new species 

 had to come from somewhere; they were not all present from 

 the beginnings of the earth. 



The study of fossil forms and geology continually de- 

 manded a greater and greater age for the earth — Bishop 

 Ussher's estimate of about 6000 years simply did not allow 

 enough time. Studies of fossil faunas showed that gradual 

 changes were the rule and that so-called catastrophes were 

 largely the result of gaps in the geological sequences of the 

 rocks. The many observations of the continuum of life de- 

 manded acceptance of the law of uniformitarianism, which 

 declared that the conditions and forces operating today are 

 like those that operated in the past. 



The "great chain of being" had now become involved with 

 the past as well as the present, and it was apparent that many 

 kinds of animals had become extinct whereas others had 

 appeared relatively late in the history of the earth — certainly 

 man was a late-comer. The idea of the "great chain of 

 being," as the handiwork of God, now demanded new crea- 

 tions for each geological period as old members became ex- 

 tinct. The possibility of new creations did not agree with 

 uniformitarianism; so a concept of the evolution of simpler 

 forms into more complex ones was necessary to fill the gaps. 

 In addition, it was observed that species showed adaptation 

 to various climates and habitat situations by morphological 

 differentiation, as, for example, the races of man. Buffon's, 

 Lamark's, and Saint-Hilaire's views on the mutability of 

 species could account for the origin of replacement species 

 without special creation. 



The concept of the fixity of the created species had now 

 become quite shaky. There were several possible interpreta- 

 tions to the observations of the schools of the "great chain 

 of being" and the mutability of species as an adaptive mech- 

 anism. One extreme was the idea that only one species had 

 been created at the beginning and that from this all animals 

 had evolved through adaptation for various niches. Another 

 was the proposal of Darwin, which assumed a continuing 

 change and modification of life with time, great periods of 

 time, and a struggle for existence — with success going to 

 that individual or population most suited to the specific 

 environment. This theory involved not just a seeking of a 



INTRODUCTION: AN HISTORICAL SKETCH 



