P^rf "VI Organismal Differentials, Organ Differentials 



and Evolution 



The students of evolution, paleontologists, systematists, biochemists, 

 and also geneticists, have used the various tissues and organs, their 

 structure, chemical constitution, their functions, as well as certain 

 peculiarities of the whole individual as subject matter for their investigations. 

 They also studied the mutual structural, functional and chemical adaptation of 

 the organs and tissues within an individaul or species, as well as their adapta- 

 tion to the milieu in which this individual or species lived. They analyzed, 

 therefore, the history of the mosaic characteristics of organisms in tracing 

 the evolution of species. In a general way, it may be stated that evolution 

 has led to a gradual increase in differentiation and specialization of tissues and 

 organs and to a more and more intricate interaction of the organ and tissue 

 constituents of the organism. On the other hand, the study of transplantation 

 of tissues, together with serological investigations, has led to the concept of 

 organismal differentials, which concerns the differences between individual, 

 species, orders and classes as such, and indicates their relationships. Organis- 

 mal differentials also have undergone an evolution, which likewise has resulted 

 in their increasing differentiation and specialization. At first only the coarser 

 differentials, those of classes and orders, can be recognized ; the mutual 

 compatibility between different organisms and their parts is therefore rela- 

 tively greater in primitive organisms. Gradually, a refinement took place in 

 these organismal differentials; they became more individualized, until in the 

 end the stage was reached in which the individuality differentials determine 

 and regulate the interaction of the tissues of which the organism is consti- 

 tuted, and in which each organism represents an autogenous system ; in this 

 condition an equilibrium between the constituent tissues and organs of an 

 individual exists only if they all possess the same individuality differential, 

 which is autogenous within each individual. Both transplantation of tissues 

 and serology have led to this conclusion. However, as we have pointed out in 

 the preceding chapters, at present it is not possible to deal with the organismal 

 differentials as chemically isolated substances ; we merely study the reactions 

 which reveal their presence, and into these reactions variables may enter, 

 which may make it difficult to determine whether certain constellations are 

 due to the lack of certain organismal differentials or to other variable factors 

 which prevent these differentials from becoming manifest. Still, the evidence 

 on hand renders at least very probable the conclusion that the lack of the finer 

 reactions in the case of the primitive organisms is actually due to the lack of 

 the finer organismal differentials, and that it is due largely to this factor that 

 the range of transplantability is wider in the phylogenetically more primitive 



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