A SKETCH OF HIS LIFE 39 



Heredity' ' remained active during life. Two of his last addresses 

 (1906-1909) deal with our concepts of heredity and variation. 

 In these he emphasizes the fact that the nature of an organism 

 is not implicit in the egg, or in the organism indeed at_ any time 

 of its life, but that it depends on a continuous reciprocal interac- 

 tion between the organism and its environment. Such interac- 

 tion leads in any particular case to a result which could not be 

 calculated from a knowledge, however complete, of the egg itself 

 since it is dependent not only on the organism but on the action 

 of the total environment. The outcome of such interaction is 

 the production of individuals which are never quite alike, although 

 they may resemble one another closely. The occurrence of like- 

 nesses, or inheritance, and the occurrence of differences, variation, 

 are thus not two processes but two views of the single process of 

 reciprocal interaction. The idea that they are distinct is an error 

 into which we fall through concentrating our attention at one time 

 on the resemblances, and again on the differences between individ- 

 uals. These considerations, he thinks, show the uselessness of 

 theories which postulate an inheritance substance and explain 

 individual differences as the result of various combinations of its 

 particles. 



These addresses show that Brooks has in some measure shifted 

 his standpoint since the time of the "Law of Heredity." He no 

 longer is in a mood to employ evolution (determinant) hypotheses 

 to account for development. He now looks on the development 

 of the individual, and that of races also, as epigenetic in nature. 

 What will be the outcome of an individual egg depends on the 

 interaction between egg and environment, not on a determinate 

 mechanism in the egg. The pre-cambrian fauna has given rise 

 to the living beings of to-day. But the latter were not implicit 

 in the former, for with the same ancestors the course of evolution 

 might have been different had the sum total of environmental 

 influences been different. 



Writings on the Principles of Science. 19 Brooks dwelt often in 

 conversation and in minor writings, and always with an earnest 



19 Professor H. V. Wilson, University of North Carolina. 



