596 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



individual, but show no direct connection with organismal differentials, nor 

 can they be strictly considered as organ differentials, an instance being the 

 four original blood groups. These substance-specificities are paralleled by 

 structural specificities. The full, complex interaction of such specificities 

 including the marked organismal-specificity in the relationships between 

 the various parts of an organism and between different organisms represents 

 perhaps the most characteristic feature of organisms: these specificities all 

 increase with increasing evolution. To such specificities of substances and 

 structures there corresponds a specificity of the reactions which take place be- 

 tween the different constituent parts of an organism, and between different 

 organisms or parts of them. These specific reactions include the normal cor- 

 relations and functional reactions between different tissues and organs within 

 the individual organism ; they include furthermore, the reactions of immunity 

 and anaphylaxis. On such specific reactions depend also, ultimately, certain 

 functional correlations between the organism and his environment, by means 

 of which the environment is distinguished from the individual's own organism 

 and, within certain limits, is reshaped by the latter, and some constituents 

 of the environment are transformed into organismal and organ-specific consti- 

 tuents of the organism. On these specific reactions are contingent, as well, 

 those functions which make possible the transmisson of specificities to new 

 generations. The problem of evolution consists largely in the analysis of the 

 mode of development of these specific systems, on which the specific reactions 

 depend. 



It is due to the combined effects of the individuality differentials and the 

 various systems of organ differentials and to the resulting organ functions, 

 that the fullest development of individuality in the highest organisms takes 

 place. But the individuality differentials, and the organismal differentials in 

 general, as well as the chemical and morphological structure of organs and 

 their functions, are themselves determined primarily by genetic factors. As 

 to the nature of these genetic factors, these differ in the case of individuality 

 and organ differentials. The various characteristics of an organ, as a rule, 

 are determined each by one or by a restricted number of genetic factors which 

 are transmitted in accordance with the laws of Mendelian heredity, although 

 various complications may arise in this process. This predominating effect of 

 a single gene or of a few genes, or of certain changes in chromosomes on the 

 ontogenetic development and on the functions of organs and tissues holds 

 good, although during the various stages of embryonal life and also during 

 adult life the cells of the most diverse tissues and organs contain, as far as 

 it is known at present, complete and identical gene sets. It must be due to the 

 interaction of the gene sets with a variety of cytoplasmic structures that the 

 differentiation of tissues and organs within the same organism can take place. 

 On the other hand, there is reason for assuming that the individuality dif- 

 ferentials depend upon a very large number of genes or, perhaps, on the 

 entire gene sets. This conclusion rests on several observations, but especially 

 on the fact that while, with progressive close inbreeding by means of con- 

 secutive brother-and-sister matings, the similarity of these differentials in 



