SOME CONSEQUENCES OF EVOLUTIONARY RELATIONSHIP 



371 



Modern techniques and instruments have greatly refined the precipitin 

 tests and revealed sources of error in NuttalPs work. Using these new 

 methods, the serums of many species of mollusks, crustaceans, insects, 

 fishes, birds, and mammals have been compared. Within each of these 

 groups degree of chemical likeness so closely parallels degree of taxonomic 

 relationship that any marked exception calls for reexamination of both 

 the serological and the taxonomic evidence. The amount of serological 

 differentiation differs from major group to major group; all bird serums 

 are much more similar than is the case in mammals, the differences be- 

 tween the orders of birds being comparable to those between families 

 of mammals. This confirms Nuttall's conclusions as to the birds. The 

 following tabulation, based on data from DeFalco (1942) and Boyden 

 (1943), illustrates the parallelism between degree of taxonomic and of 

 serological difference and the variation between major groups. 



Methods similar in principle to those used in animals have also been 

 applied to the study of plant relationships, with comparable results. It is 

 now well established that the protoplasms and cell products of morpho- 

 logically similar organisms are biochemically more similar than are those 

 of unlike organisms. This is what we should expect if the protoplasm of 

 each individual and species has its properties and functions determined 

 by the inherited gene complex. 



TAXONOMY AS AN EXPRESSION OF RELATIONSHIP 



The classification and naming of organisms, or taxonomy, arose as a 

 matter of convenience and necessity. If observations and experiments on 

 animals and plants are to have any value, we must know the species to 

 which they apply. One of the main functions of taxonomy has been and 

 will continue to be the careful description, naming, and cataloguing of 

 species. So multitudinous are the forms of life that identification of the 

 species to which a given organism belongs is more often than not the 

 task of a specialist. From this standpoint taxonomy is concerned chiefly 



