100 THE PROBLEMS OF EVOLUTION 



that the developmental powers of the gene are 

 always active; they are normally active only during 

 the period when a given character is formed. This 

 does not mean, however, that genes cease to exist 

 with the fulfillment of their destiny to this extent, 

 but only that the conditions demanding the activ- 

 ity of their formative powers occupy a limited part 

 of the life cycle of the individual. In some cells 

 even developmental capacities may be proved 

 latent, for osteoblasts, usually bone formers only 

 during development, become active again in the 

 adult under the unusual stimulus arising from bone 

 injuries. The activity, even the formative activity, 

 of genes is not limited to embryonic life nor to the 

 period of growth, and the degrees of development 

 occurring in completed individuals must be in- 

 terpreted as expressions of gene activity. Every- 

 thing which appears in an organism during its life 

 must have some foimdation in the genes. 



Still another question presents itself in connec- 

 tion with this point, viz., the sphere of influence 

 of the gene. In 1927 1 suggested a possible interpre- 

 tation. ^^ Recognizing the occurrence of a uniform 

 chromosome complex even in the somatic cells of 

 the body, it is obvious that every cell contains 

 many genes which it cannot express in its dif- 

 ferentiated cytoplasm. This means that if the 

 action of the gene is limited to the cell containing 



^^ Science N. S., Vol. LXVI, p. 328, 1927. 



